LilyPad Arduino AAA Power Issue

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

I have a LilyPad Arduino 328 with AAA power supply. I had a circuit that was working fine. I decided to add a couple extra things to it, so I stitched those on. It was still working just fine. All I had left to do was one tiny little one inch stitching to connect a LilyPad buzzer's ground. I had decided to tap into the ground for the power supply. So, I did that, but when I turned the power supply back on, my circuit wasn't working right anymore.

It turns out that it works fine when connected to the computer, so it was something with the AAA power supply. Sometimes when I flip the switch it doesn't come on at all. And when it does decide to come on, it is only putting out 4.71 volts (it used to put out 4.98 volts.) I checked the voltage on my battery, and it is 1.5 volts, so that is okay. I also checked out the power and ground petals on the LilyPad by connecting them with my own +5-volt power source (5-volt voltage regulator running from 9-volt battery, putting out 5.01 volts). The circuit again worked fine.

I need to find out why the power supply failed so that it doesn't happen again. Do they sometimes just go bad for no apparent reason? Or is it likely something I did? Because the components were a last-minute addition, I did the last bit of stitching with the LilyPad 328 main board and AAA power supply already sewn in place. The power supply was turned off of course. But I have wondered whether the sewing machine needle could have caused a voltage spike when I stitched into that trace, especially if my older model machine isn't well grounded.

Has this sort of thing happened to anyone else? Is it generally not a good idea to stitch on the sewing machine in close proximity to the board, power supply or components? Are some of them more susceptible to voltage spikes than others? Thanks for your help.

2

It almost sounds like you are drawing too much current from the AAA supply
after connecting the buzzer. Do you know the rating of the supply and the amount
of current you are drawing?

Some components are more susceptible to static than others. Some machines
can generate significantly higher levels of charge than a person. For ESD testing
there is a machine-model and human-model. Not sure about sewing machines.

The only other cause I can think of is vibration. Is it possible that the
sewing produced a vibration that weakened a marginal solder joint on the power
supply? A weakened solder joint on an inductor or capacitor could cause a lower
voltage.

If you have access to an oscilloscope you should look at the output voltage
and input voltage waveform. Since the supply seems to be basically working I would suspect current draw.

(* jcl *)

www: http://www.wiblocks.com
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blog: http://luciani.org

3

Sorry it took me so long to get back to you on this. Someone else in my household was hogging the computer.

The LilyPad AAA power supply has circuitry that takes the AAA battery and steps it up to 5 volts. Usually when I have tested it with the multimeter with no load on it, it measures 4.98 volts. The 4.71 volts was with no load at all on it, which is why I think there is now something wrong with it (plus those moments when it won't come on at all).

Another strange thing I noticed was that it was measuring somewhere from 0.5 to 1 volt with the switch in the off position. I'm not sure whether that's normal for this thing (because of, say, a capacitor discharging somewhere?---it does fall to zero after a while, so this fits that scenario).

Tomorrow I should be able to talk to the tech support at SparkFun (where I purchased it), and see what they have to say about how sensitive these things are to static of any sort. I never felt any static shock or anything, but it's possible that the machine could have caused one.

I thought of two possible solutions to keep this from happening again (if in the future I ever have to work on a circuit that's already connected).

The first would be to ground the sewing machine's needle area. And the second would be to install some zener diodes on the traces coming from the power supply, so that the current could only flow out of, and never into, the power supply. (Would that work?)

If this was a static charge that built up in the sewing machine (possible, as our house is really super, super dry), then my greater worry is about the Arduino itself, as those are considerably more expensive. I guess I'd better come up with a solution before doing any more work!

4

Also forgot to mention that before I stitched up that last little one inch section to connect the buzzer's ground into the power supply's ground, I had the connection made temporarily with a piece of conductive thread held on with a piece of tape. It was working fine while hooked up that way.

Another thing I just thought of is that I used (on the recommendation of someone else) strips of conductive fabric for the traces I added, because she said it has way less resistivity than the 4-ply conductive thread. My experiments showed that she was right---it's nearly as good as wire. I also did some of my stitching on the conductive thread to hold it in place better. It's possible that the excellent conductivity helped carry a static charge better, too!

5

It is very unlikely that static would have damaged the output. The outputs
of most power supplies have fairly large capacitors that will limit the voltage
change. If anything you would have damaged a control or feedback pin
which are high impedance inputs.

Does the output voltage change with load? Make sure you are measuring the
voltage at the power supply board.

(* jcl *)

6

Sorry, I'm not sure I'm understanding what you mean.

The power supply is a separate component from the main board. Here is a link to the product page on SparkFun for the AAA power supply:

http://www.sparkfun.com/commerce/product_info.php?products_id=8466

and here is the main board:

http://www.sparkfun.com/commerce/product_info.php?products_id=9266

Do you mean a control or feedback pin on the main LilyPad board? Or on the power supply board?

I tested the LilyPad's + and - petals (where the traces from the power supply would come in). I set up my own 5 volt power supply by hooking a 9 volt battery to a 5 volt voltage regulator. The output was testing at 5.01 volts. I connected the output to the LilyPad's + and - petals with alligator clips. My circuit worked fine that way. So doesn't that mean that the input pins on the main board where the + and - are connected are okay? If one or both of those were damaged, then I should get the same behavior with my substitute 5-volt supply, right?

It also runs fine when connected to the computer.

The only time it won't operate properly is when this little power supply is connected to it and running.

The 4.71 volt output I am reading is when I have the power supply isolated and connected to my multimeter via alligator clips:

=======
| |
| mm |
| |
=-=
ps
=-=

A little while ago, I turned it on, and nothing happened. (Usually, a little red LED comes on to indicate that it is alive and kicking.) So, I gently pressed down on the battery. When I did that, the board flexed a little, and it came on, and put out 4.98 volts. But when I connected it to the LilyPad with alligator clips, the same error occurs.

I have a circuit with a 3 x 3 LED matrix, connected just like the commercial LED matrix displays. They are all connected in parallel, with the LEDs in each column sharing a common power and the LEDs in each row sharing a common ground. (This way, the nine LEDs are individually controllable with only six wires---at pins 7 through 12.) This was working just great.

Then, I got cocky and decided to add some things. (Not sure if you have ever seen the instructable for the "soundie" (hoodie with lights and sound), but I copied parts of that. I added two circular pieces of conductive fabric and a LilyPad buzzer. One piece of fabric at a0 and another attached to ground, which I have set up at pin 4. The buzzer I connected at pin 5 (which I set up as +5v) and, as I said earlier, I decided to tap into the ground for the power supply for its ground. Everything was working fine. I had set up traces made out of conductive fabric to decrease the amount of resistivity, as some of my traces would otherwise have been pretty long. It was working fine with everything sewn but a little one inch gap connecting the buzzer's ground to ps ground.

And when I did that, I got the problems I described above.

I am reading the sensor value at a0 first thing in my loop, and if the value is > 1020 (somebody touching the conductive fabric), then I do some stuff with sound, but otherwise I just do display patterns with the LEDs. When connected to the computer or when running with my jury-rigged 5-volt power supply, the matrix LED displays run fine. When I connect the power supply and turn it on, though, it goes immediately into the routine for the sensor + sound stuff (I can tell because I do random light patterns in there, as opposed to the regular ones). The other weird thing is that the buzzer doesn't make any sound.

The sensor reading is a value from 0 to 1023 representing 0 to 5 volts, and it drops when someone is touching the two circles. It works fine, as I said before, when connected to the computer or when running with my jury-rigged power supply. But when I power it with the power supply it immediately goes into the subroutine that is supposed to be activated only when somebody is touching the fabric. (Which means the voltage has dropped at a0.) I was running this off battery power before, and it was running just fine. The first thing I tested was the battery, and I even put in a brand new one (after testing it). Very odd. Because the power supply no longer reliably comes on though, I am thinking that there must be something going on with that powered up.

Your thoughts?

7

I looked at the schematic. It is extremely unlikely that you have a static
problem. The single control pin is tied to the output and there is a 47uF
cap on the output. The input has 10uF cap.

If I am reading your post correctly when you flexed the power supply
board it started to work. This would suggest a marginal solder joint
that changes resistance when the board flexes. My guess would be
that vibration (sewing machine or handling) affects the integrity of
a solder joint(s).

Visually inspect the board looking for cracks in the solder joints.
If you find nothing then take a wooden dowel and lightly press
on the different components while watching the meter.

Sometimes there is a minimum load required for power supplies.
Since the IC on the SparkFun schematic is not labeled I could
not look it up :frowning:

(* jcl *)

8

Thanks for the information. I'll go take a look at the schematic for the ps.

One last question, and I'll quit bugging you. I'm fairly new to this Arduino stuff, and just getting back into electronics (I did a lot of stuff around 1980, and briefly in the early 90s). I haven't done a lot of buying of different components over many years, and I don't have a long history with this. So, my question is: how good are these places about taking the stuff back if you get a genuinely defective component? How can you prove that you got something defective versus you did something to it? I know I've seen signs on some websites saying, for example, "LEDs are NOT RETURNABLE." I suppose this is necessary with some components because some people have no idea how to hook the stuff up, and there's probably a lot of stuff that gets fried by user error. With the exception of the really cheap stuff (who's going to pay more than five dollars to return a 99 cent component?), I suppose all you can do is sound reasonably knowledgeable, and plead your case?

The power supply was only $14.95, so I'm not really sure where that falls on the scale of things, where on one end we have: "Oh for God's sake! Just buy another one!", and on the other we have "Egad!! I paid my life savings for this, and now it doesn't work!!" You don't want to get a reputation at these places.

I just fell asleep for about 30 secs with my nose down on the keyboard---which is a sure sign that it's time for me to go to bed. ::slight_smile:

9

That's a power nap! You're ready to go again! :smiley:

10

From my experience electronic components from top-tier manufacturers and volume distributors usually aren't defective. It is almost always an application problems.

For a hobbyist it will be more difficult to prove to reseller that the component
has a problem. The only component I have had to return in the last 20 years
was an LCD (which were $20 each). One was from Mouser and one from Digikey.
I explained the problem to each company and both gave me a credit. Digikey
told me to throw the bad display away and gave me a credit. Mouser wanted
the display back.

If you can provide a detailed description of your power supply problem to Sparkfun I
would be surprised if they wouldn't send you a replacement or give you a
credit. I would not speculate on possibly root causes for the problem (like static).
If you are fairly certain that you zapped the power supply I would tell them that
and take the consequences. Also I would provide them details on your setup and
assembly methods.

(* jcl *)