Jim's Projects

Cheap USB LiPo charger notes

Posted on October 4, 2014 by Jim

I got a couple of cheap ($1.29) 1A USB LiPo chargers since I’m doing more and more LiPo/LiIon powered stuff. I mostly discharged a recycled 18650 cell for a test load and it looks like it does charge at nearly 1A. Two LEDs – red charging, green (mine is blue) fully charged. Seems like a pretty ideal cheap device. (But see the comments for significant warnings!)

Since I use a variety of cells, I wanted to be able to charge at under 1A. Most such charge controllers have a single resistor that programs the bulk charge current, so I looked for the datasheet to find what values I’d need for the charge currents I wanted. The chip is marked 4056ES, and there are charge controllers with that number – but they don’t match this package layout. The Ebay ad was titled “5V Mini USB 1A Lithium Battery Charging Lipo Charger Module for Arduino A866”, but I couldn’t find anything under A866, either. It says RD084DY002 on the back, but that’s not helpful either. Rats. (But see update!)

I replaced the likely candidate programming resistor – 1.2K stock – with some leads so I could determine values experimentally. Here’s what I found:

  1 A   1.2K (stock)
~480mA  2.1K
 400mA  2.6K
 200mA  4.9K
 100mA  9.3K
  50mA 18.5K

Now I’m all set for when I need to deploy one.

Update 10/8/14: Thanks to Vitor, we now know the chip is a NanJing Top Power TP4056. I did a comparison of the programming resistor vs charge current info from the datasheet, and my empirical data seems reasonable. Thanks, Vitor!

Update 12/1/14: Looks like it’s actually a knockoff of the TP chip, and a possibly dangerous one at that. Thanks, Halo!

Update 11/22/16: I’m trying to design a quick, cheap, simple test jig I can run a bunch of these charger modules thru before I hand them out at a battery technology for hobbyists class. I really don’t want to hand out bad chargers!

If they come with programming resistors for 1A, how about this:

With input side disconnected, connect battery side to bench power supply at maybe 4.4V and watch current. If significant current flows, module fails. (What’s significant? 1 mA? 10mA?)
With (bench supply above removed or turned down and) input connected to power – say a 2A USB wall wart charger, running thru a Charge Doctor to monitor current: Connect a 4 ohm, 5+ watt resistor from battery output to ground and put a good voltmeter across it. At 1A, that should give around 4V, and “charging” should continue normally. Verify charging current with Charge Doctor. Obviously fail if not right.
With load resistor, voltmeter, and power still connected, connect a bench supply (good for > 1A) across the resistor and slowly crank the supply up, watching the good voltmeter. (Should probably verify first that the bench supply doesn’t do anything bad if voltage impressed across its output is greater than the voltage it’s set for.) Use Charge Doctor to verify that charging stops at 4.2V. Voltage should stay quite constant – though now the bench supply is supplying the current. What is fail level? >4.25V? or <4.15V? Hmm – I guess we should also verify that the charger doesn’t do anything bad when its output voltage remains high after it stops delivering charging current.

Does that sound good? Any other thoughts or warnings or improvements?

Update next day: Tried 2 modules, one new stock, one with resistor to charge at 42 mA. (Used 94 ohm load for the second.) Both behaved as expected, and passed all tests. Both showed 0.2V or a little less hysteresis between “done” (green LED) and charging, and went back and forth smoothly. Charging current seemed to tail off near 4.2V.

So – modules behaved OK, and tests – including the eyebrow-raising connecting a power supply to the output of a battery charger – seem to work OK. Comments/suggestions are still more than welcome.

Posted in LiPo stuff | Tagged 4056, 4056ES, charger, Lipo, RD084DY002 | 23 Comments

Adding an image to a board in Eagle

Posted on September 23, 2014 by Jim

I wanted to include a Workshop 88 logo on a board Rudy had laid out for the MAPR badges, but didn’t remember all the details from when I’d done it for the Great Global Hackerspace Challenge Educubes. This note is so I won’t have to re-invent that wheel again. It’s written for Eagle 7.1.

The basic tool is File->Run ULP->import-bmp.ulp to automagically create a series of very skinny rectangles of a raster representation of the .bmp image you provide. You can scale the new “image” and choose which layer it appears on. The script puts that image at 0,0. The first tricks are sizing it appropriately and moving it to where you want it.

How to

Begin by drawing an outline where you want the image to end up. Use the Wire tool with fine lines on a layer not otherwise much used. You’ll use this to size the new image and drag it into place. I chose layer 37 tTest and made it pink here.

Using the Mark tool with finest grid resolution on one corner, let Eagle measure the width and height of the target area. You’ll use these to decide how to scale your image so it’s just the right size.

The image must be in .bmp format. Ideally, it’s pure B&W – just 2 colors – but you’ll get to choose which colors from the image the ULP will act on. Run the ULP and choose your image. There’s a good one for W88 in the dropbox under Logos->current_logo. Select the colors you want to appear. For the one above, it’s just black.

In the dialog that pops up, I chose Format->Scaled and Unit->Mil since that’s what Eagle provides. Since my area was 413 mils and the image was 642 pixels wide, I scaled one pixel to 413/642=0.64 mil. That saves a bunch of trial and error getting the size right.

While the default layer for the (first) color is 200 bmp, that’s not a good choice if you’re using flood fill as Rudy was. You need a layer that the fill will flow around. It looks like 41 tRestrict works. When you click OK you’ll get another confirmation popup to actually run the script.

Your new image is now at the origin. Zooming way in to see the rectangles is interesting. Turn off all but 2 layers: your image layer (here 41) and the layer of your target outline (here 37). You get your image plus a nuisance freebie: tiny text with the path to your image file, below and to the left of the image. Using Delete Group, draw a box around the path and delete it. Using Move Group, draw a box around your image and ctrl-right-click drag it to be neatly centered in your target box.

Here it is in place (with layer 37 off) and after running a Ratsnest to flood fill. I don’t know how to control the width of the isolation border around the image, despite a few attempts (found it – see update). For a funny shape like this you could insert the image once oversize, run Ratsnest to flood fill, delete that image, insert the proper size one and don’t run Ratsnest again! Ugh.

Update 10/8/14: Duh! Isolation is a property of the polygon. When you click the polygon to create the outline to flood fill, there’s an Isolate: pulldown along the top. Whatever that’s set to when the polygon is created is the isolation spacing between the flood fill and areas it’s avoiding! After the polygon is created, if you look at its Properties, under Polygon Pour there’s an Isolate field. Changing that after the polygon has been flood filled even causes the flood fill to be recalculated!

Posted in Miscellaneous, PCB Etching | Tagged bmp, board, Eagle, image, insert logo, ulp | Leave a comment

Shapeoko 2 cutting tests

Posted on September 11, 2014 by Jim

Now that the W88 Shapeoko 2 (graciously donated by Inventables) is mostly working, we tried some test cuts in various materials. All were done with my old Dremel and a 1/8″ upcut end mill (WRONG: downcut; see update at end). We ran a nightly build of Universal Gcode Sender 1.0.8 (to avoid the Reset Home bug in 1.0.7) with grbl0.9g on the Shapeoko2’s Uno. Thanks to Scott for his help and consultation!

We had a lot of trouble with unexpected hard limit alarms until I disabled the limit switches in grbl. Looks like picking up noise on the limit switch wires is a common problem. We suspected electrical noise and tried plugging the Dremel into a UPS, but that didn’t help much. Next steps I’d suggest are 330Ω pullups (instead of depending on the ~20K internal pullups) and maybe 0.1μF caps to ground on each limit input, along with running shielded wires. Not sure whether to use shielded 2 conductor or just thin coax.

All the cuts were with hand edited Gcode tracing out a 1″x1″ square, with various directions, depths, passes, and feed rates. There’s lots of lessons in these cuts; I’ve only picked some highlights here.

“Foamie”

A dense flexible craft foam I seem to know as “foamie” cut pretty well. This piece was 5mm thick. One of the things we learned early on was that the wall of the cut where the cutter was going in the feed direction (maybe conventional cutting vs “climb cutting”) was much smoother than the other. You can see that effect in the far right vertical cut here. The far left cut shows that by having the cutter retrace the path in the opposite direction, the sloppy wall was considerably cleaned up. The rounded outside corners reflect the radius of the cutter.

Foamboard

I had high hopes for foamboard, but although it cut easily, the top surface tore out badly. We tried 2 approaches to reducing the tearout – both pretty unsuccessful. Here’s the result of covering the surface with blue painter’s tape and cutting through that. Bits of tape are obvious in the bottom of the cut. But the real problem was that the tape stuck so aggressively to the nice outside finished surface of the foamboard that despite careful removal, it destroyed the surface. There’s evidence that the cut edges were protected and cleaner, but tearing off the good surface is a show stopper. It could be that other flavors of tape and foam board might play more nicely together.

This was a failed attempt to protect the edges by taping a thin sheet of aluminum (pop can) over the surface. The aluminum didn’t stay in intimate contact with the surface, and so protected it little, if any. The results were about the same as with no protection – unacceptable. This is probably what chipboard would look like with this cutter. I think the blue here is from the paint on the can, and you can see little bits of aluminum that didn’t get cleaned out. On the plus side, the aluminum cut beautifully.

Foam insulation board

This is a classic material for hacker CNC machines. It cuts easily and is cheap. (A 4’x8′ sheet of 1″ thick board is maybe $15 at Home Depot; pink and blue are just different brands.) I think I ended up with good results at 1500 mm/min (1″/sec). This was an early cut when we were working through the “smooth side/ rough side” behavior. The cutter spins CW (looking down) and this cut started in the upper left and went across the top, down the right side etc, so the outside wall was cut the good way, with the fuzzies on the inside wall.

To verify the dependency on feed direction, we tried going the other direction. This one started lower right, went up then across the top to the left. Sure enough, the fuzzy side is now on the outside. This one was also testing whether reversing the path would clean up the bad wall. After it got back to the lower right, it went the other way (left across bottom) half way. The cleanup pass is quite effective.

Plastic badge material

One of the obvious target materials is the stuff name badges are often made from. A thin layer of one color is laminated over a substrate of another; cutting through the top layer exposes the lower color. The clunker 1/8″ mill we had isn’t useful for reasonable size badges/signs, but here’s the result of a quick test on an old badge. Only after cutting did I realize that the original badge – with white substrate – had been engraved and then the (white) groove filled with yellow paint! That (well dried) paint tainted the cut. The bottom surface was much rougher than I’d like, though that probably won’t matter with a much smaller cutter. I suspect the roughness was due to melting from too high spindle speed. You can also (barely) see that the cut was deeper on the left than the right. Just a reminder that when you make cuts this shallow having the spoilboard dead level is critical!

Acrylic

I really hoped to be able to do better than this with plexiglass. The spindle’s pitch change told us it needed a pretty slow feed speed. But with the Dremel at maybe 10K RPM, melting was a real problem. The circled path is way larger than the diameter of the cutter. It was essentially being milled out by the big blob of melted plastic on the end of the cutter! This makes me even more critically interested in seeing how a much lower spindle speed – with closed loop speed control able to crank more power in at that low speed – would do with plastic.

Chipboard

I brought several samples of chipboard, but after the nasty rough edges on the foamboard, I didn’t even bother cutting any. I’m almost certain the results would have very similarly disappointing torn out edges.

That said, I suspect strongly that the problem was in using an upcut spiral end mill. I wondered initially why anybody would want a downcut – since it would force the cuttings into the cut rather than lifting them out as the very reasonable upcut mill would do. But now I see: With soft material like this, dealing with the chip load in the cut would probably be worth it to get a nice clean cut at the top surface. The idea that a downcut was suitable here was reinforced when as I looked on Ebay for downcut mills I came across a set of “Luthier’s” mills for doing inlays. They would obviously care about clean edges – and those mills were downcut. Guess we need some of those, too!

Update 9/23/14 (from 9/12/14): Rats. The endmill used for all the cutting above was in fact a downcut mill. I was just being dumb when I first looked at it.

The very sad consequence of that is that my hope for better surface edge cuts with another mill were unfounded. I got those bad edges with the mill I thought was what I needed. Bummer.

Someone suggested that there’s another kind of downcut mill, with additional relief that would work better. Could be. The range of choices in cutting tool design, geometry, and material along with the real fundamentals of tool speed, feed rate and depth of cut multiplied by the variety of materials to be cut and results desired produces a mind boggling array of choices, with only a few being near optimal. It looks like a year and thousands of dollars in education to run a milling machine sensibly as a beginner. There must be an easier way. I guess the hope is that someone with the necessary education and years of real world experience will write a Dummies book for the rest of us.

Posted in Workshop 88 Stuff | Tagged grbl, Shapeoko, Universal Gcode Sender, Workshop 88 | Leave a comment

Current sink and starter’s gun boost converter test

Posted on August 12, 2014 by Jim

Background failures

I’ve had some problems getting DC power for the audio amp for the starter’s gun project. I needed maybe 15V to get the output I needed, but didn’t want a battery voltage that high, so looked at boost converters. I found some little (Chinese) boards for $2.50 on Ebay that took in 1.2V or more and put out what ever you wanted up to 30V or so, and said 4A max. Should be fine, and I can’t even source the parts for that money. I ordered some.

Running off one 3.7V 18650 Li-ion cell they put out 15V no problem. The first surprise was that when I put it all together, the whole thing didn’t work. Funny noises from the speaker, and the Tiny4313 wouldn’t even boot reliably. It took a while to figure out I was running afoul of the current limit of the protection PCB in the cell. (Worked fine with the unprotected 2P bench battery!)

While the design had been for one 18650, in desperation to get a prototype working, I put in 2 cells in series. Sure enough, now the Tiny booted, no funny noises, and it played sounds, though not quite as loud as I expected. I looked at the voltage out of the converter with a scope, and during loud sounds it dropped from 15V to ~8V! WTH?!? Going thru the doc more carefully, that was 4A max input current, and there are limitations of max output current at various output and input voltages. Rats.

Very grudgingly, I decided to try a small 12V sealed lead acid battery. Surely the boost converter will do what I need with that much voltage in. But this time I’ll actually measure and qualify the boost converter at 12V in / 15V out. Let’s see – I may need 2A (or a little more?) at 15V, so I need a resistor to provide that load. Whoa – that’s 30 or 40 watts. Using a 2W 10Ω resistor – and just at 1.5A – the resistor got really hot before I could even comfortably make measurements. Sure would be nice if I had that high power adjustable current sink I’ve thought about making from time to time. And that need brings us up to this yak-shaving project.

The current sink

Electronics

A current sink is basically a big honking transistor with a big honking heat sink, plus some electronics to let you control how much current it will sink. I should be able to come up with that out of the junk box. A little googling scored ideas that led to this as the final design: (Bonus: I figured out how to add an image to a custom library schematic symbol in Eagle!)

I found an N-channel MOSFET good for max 55V and 29A – sounds fine. A 0.1Ω current sense resistor under it provides feedback thru an op amp listening to a pot for a reference voltage (and thus current). I went with using the bench 2S Li-ion battery for the occasional use this device will get, as the spec sheet indicated the MOSFET wouldn’t turn on for many amps without > 3.7V on the gate. A voltage regulator feeds the reference pot for stability. The heat sink has a 12V fan, which runs fine (and quietly) on 8V. A switch, an LED and a couple of resistors (for LED and pot range set) plus some connectors and it should work!

It looked simple enough that I could get away with perfboard instead of making a PCB. It took longer than I hoped, but it came out OK. The lampcord is for the current to be sunk. There’s a 2-pin 0.1″ male for power in and a 2-pin female for power to the fan. The 0.1Ω resistor is across the bottom. Its long left lead is to clip a voltmeter to for setting the current (0.1V/A).

The only mildly clever bit was using some gaffer’s tape to hold the nut in place while assembling it to the heat sink. Worked well and pulled out easily. I had to grind one side of the nut down so the hole would line up.

Heat sink

I’ve never really done any proper thermal management design, so the heat sink was new territory. Fortunately, Dave has a simple intro to heat sink basics on EEVblog that got me started. Thermal resistance of a heat sink in °C/watt makes perfectly good sense. But who knows what the TR is of all the random stuff in the junk heat sink box?

I looked around in Digikey to get some ballpark numbers. The heat sinks there ranged over 3 orders of magnitude – from 0.1 to 100°C/W. Reasonably enough, the 100°C/W jobs were tiny fins you could glue to a DIP, and the ones at the other end were massive CPU coolers with fans and heat pipes. The one Dave used was ~5°C/W with no fan. If I could get to maybe 2°C/W with a fan, the 60C increase at 30W would hit ~85C – well within the operating temp of the transistor. Might work!

To be conservative, I grabbed the biggest sink I could find, and peeled the old Pentium off the bottom. Unfortunately, since it was designed for the large flat top of the processor, there were no holes in it to mount the TO-220 MOSFET. Drilling thru the fins for the nut or screw head would be a pretty ugly task. Maybe if I had a 1/2″ end mill – but I don’t. I suppose there might be one at the space, but that has problems of its own. Bummer.

The next biggest was much smaller, but had fins that allowed drilling a mounting hole – sold! Here it is attached to the finished device. (The MOSFET is on the underside of the perfboard.)

On the to-do list is putting a temperature probe on the transistor and characterizing time/temperature/power curves with and without the fan. Sure would be nice if I had that datalogger I’ve been thinking about making…

“Opportunities for improvement”

While the current sink was a junk box special, I did try to think it through. For example, I wanted to be able to run with or without the fan. But did I really need another switch? Naw – the 2 pin connector would be fine. Did it really need an LED? Yeah, I could imagine accidentally leaving it on. And I dry fitted the parts to make sure it would all go together. But I still had 2 surprises – one electrical and one mechanical.

The main consideration in something like this is handling the power – and getting rid of the attendant heat. I put some moderate effort into the heat sink to do that. If it can dump 30 W or more without the transistor going above maybe 85C, it should be fine. The MOSFET is good for 29A, so current isn’t a problem.

Well, not for the transistor. But what about that 0.1Ω current feedback resistor? I’d like to be able to do 10 or 20 A. But wait – at 10A that resistor will dissipate 10W! With the 2W resistor I used, it’s only good for ~1.5A. Boo. I ordered some 20W 0.1Ω resistors to upgrade it some day. 0.1Ω resistors don’t usually manage to get very hot, but I guess this isn’t a usual application!

The mechanical issue was pretty bad, and I really should have seen it coming. The only mechanical connection between the heat sink and the perf board is the MOSFET – or more accurately the 3 legs of the MOSFET’s TO-220 case. To allow for some air flow past the transistor, it’s 1/4″ off the board – with only those spindly legs in between. The pot – which is manipulated a lot – is screwed to the heat sink – so that’s not a problem. But the power switch and the connector for the battery are on the perfboard. And every time I touch either one, the board woggles around dangerously.

There’s a nice chunk of aluminum very near by, and I could drill and tap a hole for a screw. But I don’t have much real estate left on the board, and if I used a plastic spacer I’m not sure how it would do with a hot heat sink. I’m sure I’ll come up with something, but catching it earlier would have been good.

Update (next day): OK, this is crude, but it keeps the board a lot more stable, particularly when I operate the switch. Good enough.

Update 11/8/17: The $150 Basement Watchdog brand battery for the backup pump installed 2/17 seems to be bad. WTH? I wanted to do a discharge test on it, and the current sink seemed appropriate, but the 0.1Ω current sense resistor would limit the discharge rate. It’s finally time to put one of those 20W jobs in.

Mechanical mounting is fine, though I’m not proud of the blob-of-solder electrical connections. But it looks like it works. I used the new bench supply and ran up to ~5A. The voltage side of the supply was set to 8.7V, so it was drawing ~50W. The power supply fan – which I’ve never heard before – came on promptly. I adjusted the sink for about 3A just so the supply wasn’t at one of its limits. The current sink’s heat sink was quite warm (its fan, powered with the 7.4V bench battery, was on). When I turned the voltage down to ~0.5V, the current (voltage across the sense resistor) stayed just about constant, and the power supply’s fan went off. Looks like it’s all doing what it should!

Back to the task at hand

Now to take a closer look at the little boost converter. I don’t know how it works, but I wonder if a larger cap on the output would help keep the voltage from drooping? Hmm – looking at the board, the larger cap in on the input. Is that just another student error? These things are usually exactly from the example schematic in the datasheet. Let’s see…

Gee – it shows a 220μF on the output – and the board has a 220 on the input. Pretty suspicious.

Ooh – a shiny thing to distract me!

Looking at the schematic, I realized I had no idea how this thing worked. OK – output cap, voltage divider on the output for feedback, some kind of enable, yeah, yeah. And all the current that goes to the output goes thru the inductor. Oh – except for what comes from that “SW” pin. What does that do? <checks block diagram in datasheet>

Hmm – nuthin’ comes out of that pin. All it has is a MOSFET to ground. So all it does is … SHORT OUT THE INPUT AND OUTPUT TO GROUND! WTH?!? Oh, that’s what the diode is for: it doesn’t short out the output. But it still shorts the input to ground! OK – thru the inductor, but still…

<light slowly comes on> OK, as soon as the switch comes on (connects to ground), the whole input voltage is impressed across the inductor. There’s no current spike – since the inductor “doesn’t want the current to change”. But as the current slowly builds, it’s storing energy in the inductor. When the switch opens, the current thru the inductor would drop, but there’s a big inductive spike as the inductor keeps the current flowing. Where does it go? (Thru the diode and) into the output cap! Aha!

So what does that inductor-driven ripple look like? And is it better/smaller with more capacitance across the output? <hooks output to the new current sink and puts scope across the boost converter output>

Here’s the output voltage (AC coupled, 20mV/div, 1μs/div) at 0.5A stock (left) and with another 100μF across the output. <scratches head> So maybe with more C there’s lower impedance to the high frequency component of the inductive spike, and we see it as a leading spike on output voltage? I’m really not sure how it’s all supposed to work, but there’s a gut reaction that says those near-square waves from the stock config indicate that the inductor and stock cap are about ideally matched, despite the 220μF value in the datasheet example.

I suspect the tilt in the stock picture is the cap being discharged at constant current. Let’s see: Stackexchange says discharging a cap at constant current gives a rate of voltage change of I/C v/sec. That’s 0.5A/100μF=5V/ms, or 5mV/μs. Eyeballing the 2 slopes of the waveform (bottom is steeper), it’s maybe 0.25div vertical per div horizontal. At 20mV/div, that’s 5mV; horiz is 1μs/div; so that’s about 5mV/μs!

Hmm – so if I change the current load, the slope should change. <goes back to bench> Well that was interesting. Here’s the output ripple at 100mA and 800mA. Starts with the bottom flat and the top tilted, ends the other way (plus greater overall amplitude). Slopes were the same around 300mA. I have no idea what’s happening.

And then there’s the question of why the datasheet shows a 33μH inductor and the one on the board is marked 330… Update: Duh. 33*10^0. Thanks, Michael!

Back to work

So why were we here again? Oh yeah – does additional output cap make less droop? And the original question: how much current can the booster put out at 12V in/15V out? Looking at the output voltage on the scope (DC coupled) when it’s dropped down to maybe 12V, touching an extra 100μF across the output does bump the output up by maybe 0.1V – not enough to do any good.

The output voltage really hits a wall as current increases above about 1A. There are significant thermal effects in the booster, so it’s hard to get good measurements. Output is still 15V at 1A, but by 1.2 or 1.3A output is down to ~13V. By 1.5A it’s below 11V. That’s not great news. One amp is 15W DC in to my audio amp, and the amp isn’t 100% efficient. I’m afraid that makes a max output of 10 or 12W – less than I’d hoped for. But now I know. Let’s see if it’s loud enough.

So the actual testing that started the current sink project was almost trivial once I had the tool. But making the tool was fun.

Posted in Miscellaneous, Rf starter's gun | Tagged current sink, heat sink, IRFZ34N, XL6009 | 4 Comments

Tiny85 dev/target boards

Posted on July 2, 2014 by Jim

Just a quickie, but it seems to delight me. I finally got around to making up a little bunch of generic Tiny85 boards so I can knock out some simple projects. They’re a lot like the I2C slave boards for the dollhouse, but have all the pins brought out and have a 6-pin ICSP header so programming is easy. I laid out the board several months ago, but hadn’t gotten around to making any.

Of course, the first one didn’t work. I’m pretty good about putting a mark on the PCB for Pin 1 on ICs and connectors, but I missed it for the Tiny on this board. (It’s fixed now 🙂 No problem – the board is so simple I can reverse engineer it visually. Let’s see – I always put a pullup on the RESET pin, and there are only two 1206 pad pairs, and that one is a jumper, so the pullup must be here – and that goes to the Vcc pin, which is pin 8, so the chip must go this way. Done! I put all the SMT parts down and reflowed it – and it looked about perfect. A couple of minutes to hand solder the header, and it was time to test.

But it didn’t even get as far as running avrdude for a signature check. As soon as I plugged it into the Arduino ISP, all the lights on the Arduino went out. I held it to my lip, and the Tiny was fairly warm. Not good. Then I proceeded to make myself crazy trying to more carefully reverse engineer it visually. Was the header layout backwards so the pins came out the back of the board? Did I actually lay out that nice big ground pad wrong?

When I finally looked up the original Eagle layout files (like I should have in the first place!) it became frustratingly clear: I didn’t put a pullup on RESET (it’s not really needed) – and those pads are for a cap across +5/Gnd, not a resistor! And sure enough, my reverse engineering based on the non-existent pullup led me to put the Tiny in backwards! Rats.

I made up another board (correctly, this time), and it worked first try. Same for the next one, and the same for another set of 3 I reflowed all together. So I had 5 working boards plus the bad one (now with an X on the back, since they all look very similar) as a continuous reminder of my sloppiness. Guess I better fix it. (The picture was taken before the fix. Can you find the one with the Pin 1 dimple opposite all the others?)

Hmm – it really should just be a 5 minute job with the hot air station. But did I fry the chip? (Fires up the hot air.) Eight minutes later, reusing the original Tiny, I had another working board! To reward the board for surviving being powered up with the chip in backwards, I even replaced the wimpy green LED with a nice bright red one. Now I not only have 6 boards at the ready, but no longer have the reminder dud staring at me. (And I got to wipe that big X off the back!)

Applications

What will they be used for? One of the first applications will be a beeper to remind me the hot melt glue gun is plugged in. When I need it I plug it in and, having better things to do than watch the glue melt, walk away. I usually come back a few minutes later to use it. But sometimes it’s an hour. And once it a while it’s many hours. Ouch. So one of the Tinys will wait until the gun is hot (open loop timing), and sound a piezo buzzer once. A minute later, 2 beeps, then 3, etc. That should work well. (When I get around to making it.)

Another application will be making the house stereo amp more robust. The dumb Sherwood RX-4109 that lives in the basement (always on) and drives speakers in the kitchen, living room and bedroom has a ‘soft’ power switch that defaults to OFF after a power cycle. Since the music it provides is also my alarm clock, the priority of a fix jumped much higher on the list after I overslept the morning after a brief power outage shut it off.

I’ll decode the Power ON sequence from the Sherwood’s IR remote, program a Tiny to reproduce that signal to drive an IR LED taped to the front of the amp, and have the music startup script tell the Tiny to send Power On to the amplifier every time some music starts. Overkill, but at least it should always come back after a power failure. Since the music script is on the main PC, I’ll have to invent a channel to send a message to the home automation system which can in turn actually operate the IR sender Tiny. Several steps, but it will be nice to not have the (upstairs) music fail after a power failure.

Update 10/3/14: Not related to Tiny85s, but just to the dumb Sherwood receiver: I won’t need this Tiny app, as the problem has been resolved. Someone donated several dead UPS units to W88. I brought an APC BackUPS 350 ES home and (as expected) the only problem was a dead battery. In an interesting lesson about industry standard battery sizes, I was able to remove the stock 3 A-hr 2.6″x5.25″x2.7″ 12V SLA battery, and by breaking out a bunch of support webs, drop in an old, much larger 7.2 A-hr battery that fit perfectly! It had been removed (I think) from a B&D string trimmer and found to only have 2.4 A-hr capacity. That’s plenty for this app, and the battery worked, fit, and was free. The receiver is now on its own UPS, and should survive at least short outages without turning off. A perfect, free solution!

Another possible application will be at least doing initial datalogging to see how much power I can get from a small solar panel in a tree where I really want to put a camera looking at the house. Solar (or possibly wind?) is the only way I can power it to take a picture every few minutes and radio it back to the house. Doing this initial energy monitoring/logging has been on the list for oh, maybe 5 years. Maybe these Tinys will let me make it happen.

But just having that little stash of Tinys there – each one eagerly awaiting its chance to serve – gives me a little delight each time I see it.

Posted in Tiny 85 stuff | Tagged Tiny 85 | 3 Comments

Quickie 1-cell discharger

Posted on June 1, 2014 by Jim

Wow – I wasn’t planning to make this. But as I fantasized about just building a simple discharger while struggling with 1-cell problem on the big 18 cell discharge tester, it sounded too simple to resist. I could get to a couple of analog inputs and ground with a mini-shield just on one side of an Arduino. (And I seem to like mini-shields.) And a MOSFET instead of a relay would make it simpler and more robust. It sounded so simple I just made it up on perfboard rather than laying out a PCB.

The extra juicy bit of simple was realizing that the Drain-Source resistance Rds was pretty constant, and for this MOSFET was in the neighborhood of what I needed for a current sense resistor. If I put the MOSFET at ground and measured the voltage on the Drain, I’d have the current reading – for free! And it doesn’t take a fancy 1% 0.1Ω resistor – as long as it’s a fairly constant value, a calibration constant in the code will deal with it.

It uses screw terminals to connect an external load resistor like the big discharger, but stayed very simple with just a single pair of clip leads for the single cell. An LED on the Gate (really on the Arduino pin driving the Gate) to show when it’s discharging is nice. The 1.1V internal reference on an Arduino (328P) is fine for the current sense, and just took tweaking a voltage divider to make a good fit for the voltage sensor. Setting up for ~5V full scale gives me very good resolution for either 1.2 or 3.6V cells fresh off the charger. By putting in an extra pin, it’s pretty unambiguous how it aligns with the Arduino header pins. (OK, unambiguous on a Duemilanove, though not on a Mega.)

The code was pretty simple, and as it matured, I was able to steal some bits from the other discharger code. The one open issue at the moment is to verify whether Rds is constant enough to treat as a constant for the current sense. I guess worst case I can code up a piecewise fit for it. (Done – see update.) But the device is booked solid for a while testing some AA NiMH cells, so I can’t even get it to the bench for the calibration/linearity test.

Ever infected with the “Ooh – and with just a little change I could make it do something even cooler…!” bug, I thought about making up a PCB and having it as a giveaway tool for a class on battery tools and technology. Like I need one more prep-for-a-class project on the list. But if I were to do that, the choice of MOSFET becomes important. I even ordered some nice ones with Rds of 20 milliohms or some such, but they’re not ideal for the Rds-as-a-current-sense-resistor bit. It’s kind of interesting to need to select a part with resistance not too high but not too low, either!

Anyway, I’m surprised with how pleased I am with this little guy. The fact that I can just throw it on an Arduino, and that I didn’t even have to make up a PCB means I’m not even sad it’s not Tiny85-based. The fact that it’s completely junk box parts makes me smile, too. This little bit of perfboard’s a winner!

Update 6/2/14: Here are the results of a current calibration on the bench (all in mA):

Actual    20   50  100  200  300  400  500  600  750  1000  2000
Reported  14   45   96  197  308  420  545  675  840  1200   1700
Corrected      55  100  189  288  387  498  612  739  1015

Between those observations and the datasheet, it looks like at Vgs of say 4.8V we’re at the edge of linearity of Rds at an amp. The transistor got quite hot at 2A, so it looks like the practical upper limit is 1A. The current calibration constant is 1.67mV/count, so we’re at the ragged edge of digitization problems at say 20 mA. Let’s say a practical lower limit is 50 mA (and rocky at that).

Taking the A/D count as Reported/1.67 and doing en embarrassing amount of manual cut and try in Excel, a final formula with corrections (A/D count=A): (A+10)*1.48-(IF(A>400)then((A-400)*0.2); else 0)) gives a pretty good fit over the range of interest. (Apologies for the Excel expression.) Red is ideal, green is corrected. Guess I better code that in (and test it again 🙁 ). Done.

Selection of a new MOSFET for building multiple units would like:

Max continuous Ids > 2A, Vds > 5V (trivial)
Rds(on) ~0.5 ohms (requires finding suitable part)
Vgs of 4.5V fully saturates at 2A (requires finding suitable part)

OK, now I’m pretty comfortable with the current calibration, know the device limits and what next steps might be. I’m still really pleased with this little guy. And it’s done!

Update 11/12/17: This device was just pressed into service again (in a capacity it wasn’t designed for), after a fair struggle trying to figure out how to do a discharge test on a BWD sump battery. Its existence emerged only slowly out of foggy forgetfulness. I was very glad for these notes, first to remind me of the device’s existence, and then for enough detail to put it back to work in a new Rube Goldberg configuration. Details here. <link to not-yet-written post>

Having a newly updated Tiny84 datalogger, and using the big current sink instead of the external resistor usually used with this discharger, all I needed from this was voltage monitoring to cut the test off at a reasonable voltage. I found the dongle with a 12V automotive relay from some other 12V discharge test, and thought I could use this one just to control the 150mA to that relay to provide the shutdown function.

Can I get away with 12V?

Looking first at the 3.3K/12K divider for voltage sensing, I was pleased to see that it would work as-is for a one line code change by just used the 5V analog reference rather than the 1.1V one. I didn’t care about the current monitoring part, as I planned to set that manually (to a fixed 3A) in the current sink. Ignoring it was a nearly very costly mistake.

Having the 12V relay’s path to ground switched by the MOSFET was fine, and the 150 mA coil current was easily within the MOSFET’s specs. But because of the current monitoring approach, the voltage on the drain – 12V when off – was directly connected to an analog input pin (A4) on the Arduino. That’s not fine at all.

But it was much worse than potentially blowing a $3 Arduino. (Hmm – I should check to see if that analog pin still works!) The 12V fed back thru the USB connector to my nice new laptop, crashing it so badly I had to pull the battery to get it to turn on again. (I was very sad and mad until I tried that, fearing that the laptop had been damaged beyond repair.)

Making it even worse, my first thought was that it was a ground problem through the laptop’s power supply. (In hindsight, it’s probably isolated, though I really should check that out.) I’d needed to do the additional very non-standard thing of reversing +/- connections to the relay dongle, as it was wired to need +12 to the coil, whose other end was grounded. So after the first crash I pulled the laptop’s power supply and ran – obviously completely isolated – on battery. It crashed the PC hard again. The second time I got it running again still sitting on the floor in the power tool room by pulling the battery. Much shorter panic duration, but still very unhappy.

Thankfully, looking at the schematic again provided the insight that the 12V was directly connected to an Arduino pin (when the MOSFET was off). Using some jumper wires to connect this mini shield to the Arduino – without the current sense pin – allowed it to work as needed.

The takeaways are: 1) Don’t use this device for > 5V without somehow disconnecting the current sense pin; and 2) Don’t be sloppy cobbling things together to use higher voltages than they were originally designed for!

Posted in Little Discharger, Tiny 85 stuff | Tagged Arduino, battery discharge, mini shield, MOSFET, perfboard | Leave a comment

Battery discharger problem with 1 cell

Posted on May 31, 2014 by Jim

The big battery discharger works well (or so I thought) except for the case of testing single 1.xV cells. It just doesn’t work – reporting 0V often. There’s even a comment in the code dated 2/15/11 (right under the V1.3 update comments) that it doesn’t work with 1.5V cells. The comment was that the A/D returned 0 counts, and that it worked with 2 or more cells, and that I hadn’t looked for the threshold.

I had a bunch of NiMH cells I wanted to test and had forgotten about this problem. After going thru 3 battery holders, I started to make better observations, and rediscovered this problem. There are various debug prints commented out in the code, so it looked like it wouldn’t be too hard to figure out what was going on. (Wrong.)

To get a handle on what voltage the problem happened at, I hooked a 2.5K pot across my good bench Li-ion battery for a stable adjustable voltage source. I put a good DVM across the main discharge leads (clear zipcord, R/B clips). The discharger code displays the voltage across the main leads while waiting for a CR to start the test. That should be a good test setup.

With the pot in the middle, the voltage on the DVM bounced all over the place – by several tenths of of volt. After a bunch of head scratching and other test configurations – including using the (AC) bench scope while powering the Arduino with the 1xAA 5V supply, I’m fairly confident in the following observations:

There is a substantial – tenths of a volt or maybe much more – noise signal on the main discharge leads. I think I saw it as a more or less a symmetrical sawtooth.
As I watched the “waiting” output voltage indication and played with the pot, there seemed to be a threshold around 2.1V. I’d occasionally see values in the range 0<V<2.1, but never stable. But that 2.1V indication was NOT at a pot slider value of 2.1V! There’s something VERY wonky about the voltage indications at low values. A few points: (Actual=pot set with leads disconnected, Reported = leads connected)

Actual V    0.06  0.11  0.65  1.0   1.4   1.5   4.0
Reported V  2.1   2.5   3.5   3.6   3.75  3.75  3.98

With the pot set for 1.40V (measured with the discharger leads disconnected), with leads connected, the DVM bounced between 1.41 and 1.82 (watching for a minute or so).
Hmm – that’s not consistent with the misbehavior: With a AA NiMH cell fairly fresh off the charger and measuring 1.38V, when I connected the main leads to it, the reported voltage dropped instantly and consistently to 0. With the leads floating, they showed ~4.1V. The source impedance of whatever’s on those main leads is very unclear.
Scary question: Does this mean all the tests I’ve done for the past few years (on higher voltage batteries) have produced inaccurate results?
For reference, here’s the board as it has been in service for the past couple of years. From what I can see/reverse engineer, the voltage out of the mux (from whichever input lead) goes thru a 12K/1K voltage divider (0.077 of orig) to Arduino A/D input A0 which is referenced to an external (on the discharger shield) 1.88V zener (sourced from 5V in from the USB/serial connection). That would give a theoretical max voltage of 24.4V for 1024 A/D counts. (Reasonable for nominal 18V Nicads, which were the original max target.)
Continuing the theory, that would give a formula of (A/D counts) * (24.4/1024=.024) to get actual voltage. The code has a comment with that as the “expected” value and a #define of 0.0263 as the working calibration constant. For a 1 V input that would give around 38 counts on the A/D. Not a lot, but unless the A/D isn’t working well, it shouldn’t give any weird threshold effects.

I’ve spent way more time than I should on what I thought would be a fairly quick fix, and am grudgingly pulling the plug for now.

Next steps

Put a bench supply on the 1K/12K junction and watch the indicated “waiting” voltage compared to actual. Yeah, I’m driving one side of the mux with that, but it’s thru 12K. Hmm – seems to me the specs of the mux chip say no inputs > some V+ voltage. I think that means I need to put at least as high voltage on the main discharge pins (which go to that V+ on the mux) as I’ll put on the mentioned test point. (That jives with a vague recollection of strong requirement that the outer ends of a battery MUST be connected before any of the per-cell leads.) Maybe a red LED to make that V+ about 1.7V higher than the test point? That ought to do it. Heck, even a Schottky should do it. Next step after that depends on what we see with this (if I ever get time to do it). But at least these notes will help me remember what I saw today.

There was a lot of daydream level consideration given to making up an even more “appliance” discharger, maybe for just one cell, probably with a Tiny85. By using a 1:1 voltage divider with 1% resistors (maybe 4.7K?) and the internal 2.56V band gap voltage reference and 5V power from the fake FTDI cable, it should handle a fresh 4.2V lithium cell and give good resolution. I even ordered some IRLB8721 MOSFETs with ~20milliohm RDS(on) for the discharge switch. (Thanks to Adafruit for choosing that part!) They’ll handle several amps, so keeping the external load resistor approach, it would handle most everything I’d be likely to throw at it. If I just had time to build it…

A little later: Oops – on 328P it’s a 1.1V reference. Rats.

Posted in Discharge tester - PCB build | Tagged battery discharge tester | 1 Comment

Working with recycled HDPE

Posted on May 26, 2014 by Jim

This is just draft stuff – sort of so I might remember things I did. Needs actual rewrite, pictures, more meat. But at least I have a place to capture some efforts.

It really seems like scrap HDPE – like from milkbottles – should be a wonderful source of material for making stuff – if I could figure out how to work with it.

Some time ago I tried to melt sheets of HDPE from milk bottles into a sheet maybe 6″ square. A few layers between sheets of silicone parchment on a cookie sheet with a flat piece of metal on top and an anvil to smush it in the over at what – 250? – for half an hour or something. Results were poor – lots of voids, poor adhesion. Needs more pressure (force/in²) to stick. Or maybe more active smushing/working. I really thought I took pics of that, too, but can’t find. Or maybe I just planned to take them. I’ve seen several videos of people making flat stock from scrap, but most cut it up really fine before melting. Seems like a lot of work.

Inspired by maybe a youtube of an Indian kid repairing plastic buckets on the street with a torch, scrap plastic and screen?paper clips?, I thought I should try some repairs. Other videos showed others doing HDPE repairs, like on canoes and water tanks using similar methods. There’s some skill to it that will come with exposure and familiarity with the materials.

Did a repair of a broken Rubbermaid laundry basket handle with hot air station. Came out OK. Some hardware cloth for reinforcement one place, wire in another. Used milk bottle plastic for welding rod. Not ideal – seems to have higher working temp and less soft than original. It was easy to melt thru original, and when I did it was almost liquid. The Milk Bottle HDPE (MBH) didn’t get that soft. Made a smoothing tool and a poking tool – both quite useful. I think cooling/wetting the smoother in water helped. Thought I took pics, but can’t find.

Did a second almost identical repair with almost identical results. Again used sheet patches of MBH over the very rough top of the handle. Made it considerably smoother. Took several minutes with a new Xacto knife to make it feel fairly nice. Sanding would have made it smoother more easily, but not left a polished surface. Maybe I could have flame polished it afterwards? Meaning hot air probably rather than flame – but should try it with a torch as well. If that worked, it would be faster and better.

Still looking for softer welding rod, I tried strips of plastic grocery bags. Finally made a strip maybe 1″ wide, twisted quite tightly, then sort of fused while twisted with hot air. Didn’t make nearly as nice a rod as I hoped – didn’t stick together well. Anyway, it didn’t melt any better than the MBH, so nice try but no cigar. I have an old dish drainer I should try to use for scrap.

I’d really like some softer stuff for welding rods, especially for those laundry baskets. Maybe Rubbermaid stuff from Goodwill?

I’m considering fusing some MBH together for a bottom bracket for the 1/2″ PVC AA battery trickle charger tube. Shapelock would work fine, but it’s infinitely more expensive than free MBH. Actually, what I’m thinking of is using MBH sort of like Shapelock but at higher and harder to manage temps. Yeah, I could make the whole bracket from wire, but plastic would be nicer. Maybe just acrylic. Or maybe shut up Jim, and work on what you’re supposed to be doing.

Posted in HDPE | Tagged HDPE, recycle, repair, welding | 3 Comments

Protected: RF Starter’s gun project status

Posted on May 26, 2014 by Jim

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Car has music again!

Posted on May 23, 2014 by Jim

It’s always nice when a little DIY work can save you $30,000.

The 6 CD changer in the Prius wouldn’t play the other day. I noticed a CD partially ejected and when I couldn’t get the unit to eject it, pulled it out by hand. It has never played or loaded or ejected a CD since, showing errors including “seek error”. (The radio still works fine). A little googling revealed that a jammed changer seems to be a common failure in the Prius, and that having Toyota replace it might run $1000. The car has just about 100,000 miles, so I took it as a sign that it was about time for a new car.

I don’t know for sure what happened, but I suspect the “eject” button was hit accidentally, and the supports for the new GPS prevented the disc from ejecting fully. Thwarted by the failed eject, the mechanism damaged itself and got stuck in an unrecoverable position. But that’s just a guess.

I’ve long wanted a better aux input than the cassette tape spoof, but hadn’t found a cheap way to do it. Google showed that others suffering from the jammed changer syndrome elected to add a third party input adapter, usually including an iPod interface that was actually integrated into the car’s audio controls/display. I’ve never owned anything Apple, so that was uninteresting, but integration with the MultiFunction Display and steering wheel controls was very attractive. With no music in the car, the $100 price tag for an adapter suddenly seemed less of a show stopper.

I exchanged a couple of emails with GTA with questions about the unit. They were very prompt and provided completely helpful answers, so I would happily recommend them to anyone else considering such a purchase. I ordered a GTA Car Kits adapter ($115), a beat up 4GB iPod Nano ($22) and cable ($1.45!) from Ebay and a few days later had new toys in the mailbox. A youtube video from GTA showed how to tear the dash apart to get the old radio out. Doable, but a big production. Thankfully, they also provided a “shortcut” video that provided just enough access to get your hand in to plug in the cable by pulling only the glove box (trivial), the right center vent panel (no tools) and a wiring distribution block (one 10mm bolt). Given those choices, I decided not to even bother trying to (remove and!) fix the changer. The 3 CDs still in it will go with the dead car to the crusher.

The one 12 pin connector from the GTA adapter plugged into an open connector in the back of the changer (despite the fact that they sent a Y cable for those connectors). Apparently the nav system is connected similarly. I think the TX+/- are data for a CAN bus. That discovery led to a rabbit hole of reading about CAN bus info and hacks. There may be multiple such busses in the Prius, but an interesting one is accessible through the ODB-II connector. Hey – I bet I could get a $12 ODB-II USB or bluetooth adapter and look at all kinds of stuff going around the car network – maybe even the text of song titles from the iPod! And I’d been thinking about getting a cheap ODB-II tool just so I’d have it if I needed it for diagnostics. But in a rare moment of restraint, I listened to the little voice that said “Let it go, Jim!” I really don’t need more hardware to add yet another project to the list.

Back to the task at hand, I decided to mount the GTA unit to the wiring distribution block. Some inner tube rubber should keep it from slipping around. The connectors for the iPod cable and a 3.5mm aux input jack were still accessible by just dropping the glove box. Looks fine.

While the main glove box is always full of stuff, the top compartment is quite underused, and looked like a good location for the iPod. Some closed-cell foam made a reasonable grommet for the cable as it exits a 1/2″ hole drilled in the side of the compartment. Though not visible here, I did notch the corners to make it slightly more grommet-shaped and help it stay in place.

A gracious loan of a 30 pin Apple cable from Mike M let me start playing with the iPod a few days before the cable I ordered came. Putting music on the iPod was an ordeal, though mostly of my own making. In trying to use good old Winamp playlists with it, I formatted the flash, making it unusable with the GTA adapter. Due to a parallel project repairing a square dance recorder, at one point the iPod had a Rockbox firmware directory on it. Oops. ITunes was unable to “restore” the iPod firmware despite several attempts. Fortunately by installing iTunes on another computer I was able to get the iPod “restored” so it would once again work with the GTA adapter. Of course that meant that I’d have to use iTunes to put music on it.

While I eventually made peace with iTunes, I swore at it a lot in the beginning. I tried to create a login, but when it required a credit card, I gave up. It said I could just drag and drop .m3u playlists in, but they came in empty. I got some malware while installing a tool to convert .m3u playlists to Apple (that didn’t even work). I eventually found a forum post saying .m3u playlists would work, but only if they had full paths. After globally prepending “I:” to the file pointers beginning with just “\mp3\playlists…” the playlists imported to iTunes OK – and brought all the associated music files with them! There was a bunch of time spent deciding on and cutting down playlists to limit the music to about 45 hours to fit the 4GB flash, but that wasn’t iTunes’ fault. I’m still not comfortable with iTunes, but it got the job done.

With the iPod plugged in, sure enough it showed up as CD Changer 2! Of course the original non-functional one still showed up (as CD1), but I could skip over it with the steering wheel Mode button (but only that way!). Disc 1 shows up as “Hybrid”, and might play the audio from either iPod or 3.5mm jack (or both?), but discs 2-6 are Playlist 1 – 5. The 6th playlist shows up in some places as “Disc 7”, but there’s no extension of the Disc 1-6 display. While I’d told the iPod to “Shuffle 1 Playlist”, each playlist seems to play in order unless I touch the Disc Rand button. Not a big deal. And when I touch Title, another screen shows the actual track title! I never found a way to name the playlists, though.

Here’s the iPod in its final bubble-wrapped home. It’s completely functional, sounds great, and is exactly the hands-off installation I’d hoped for. And now that I have music again, it saved me from having to buy a new car!

Posted in Miscellaneous | Leave a comment