Computing stuff tied to the physical world

AA board testing

In Hardware on Sep 23, 2010 at 00:01

The latest AA Power board is one of those ideas where I can’t help but think… why didn’t I think of it before?

There’s a definite cost trade-off (that LTC3525 is expensive, and it’s only available in SMD so it has to be assembled), but I’m definitely going to switch my room nodes over to it – once that elusive how to enclose it? question gets answered, that is…

Anyway. I’ve been assembling dozens of those boards lately. Hand-soldering them, in fact – because the paste stencils aren’t ready yet. The soldering part is easy, I’ve got that down fairly well nowadays. I like soldering.

The issue is that each board must be tested. Recalls are tedious / inconvenient / annoying for everyone, and not just embarrassing for me, but totally robbing me of my pride in what I do and what I make.

Doh. Welcome to the real world.

Time to use those Pogo test pins. The nice part is that the AA Power board is ridiculously easy to test: apply 1.5V and watch 3.3V come out. Or, more loosely: connect it to an AAA battery, and watch it drive a green LED.

Here’s the AAA battery + green LED + Pogo pins part:

Dsc 1961

Note that there is no circuit on this board – no components, just the missing pieces.

To use it, I simply push the board under test against it, and voilá …

Dsc 1962

If it lights up green (see lower right corner), it works!

Great time saver. Caught about 1 in 10 (mistakes on first test), until every one of the first 50 boards was working.

Onwards!

  1. Mr JC, what’s that I see? An alcaline battery?!!!

    Tut tut tut!

  2. Suggestion for improvement, so that the test delivers more information than just “there is some voltage coming out of this, high enough to light the LED and low enough to not destroy it”: Connect a JeeNode to the test rig, let it measure its supply voltage via a voltage divider on one of the analog pins and indicate via an LED when the voltage is within the specified range. With three LEDs you could even make it a bar graph that goes from “too high”, over “high but still ok”, “perfect”, “low but still ok” to “too low”.

    • Good point. Note that the ADC is ratiometric, and the output is 3.3V, so the JN regulator is not active, just dropping a tiny bit. Can be done, by comparing against the 1.1V bandgap reference – needs a simple divider to get the input voltage into the proper range.

      You could even turn on the RFM12B transmitter, and check that the voltage remains stable under load…

      To be honest, I probably won’t go there now (test jigs for several other plugs are higher on my TODO list) – but it’s definitely a good refinement.

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