2 Keith and I have been plugging away for the last couple weeks
3 turning on and testing the various
4 bits of [TeleMetrum](http://altusmetrum.org/TeleMetrum),
5 and I can now very happily report that we have all the hardware
6 working! Amazingly, we got almost everything right in the
7 hardware design. Only two things need to be changed.
9 We need to be able to control the chip select line on the the SPI
10 non-volatile memory chip, which means we need one more GPIO line to it
11 from the processor. To free up a line, we gave up the ability to put
12 the accelerometer in to self test mode. Two trace cuts and two jumpers
13 to the current board implement this change.
15 The last thing we got working just this evening was the ability to sense
16 the presence of an ejection charge igniter. We need another resistor in
17 each of the two sense circuits to form a voltage divider so that we don't
18 overload the ADC input. Not sure how we missed that in our many design
19 reviews! Oh well. To ensure robust ignition of the electric matches
20 we prefer to use for ejection charges, we charge a 1000uF cap to a voltage
21 higher than our ADC inputs can handle. Fixing this problem on the current
22 boards requires changing the values of two resistors, then tacking extra
23 resistor to one end of each of the existing ones and then wiring the other
24 ends of the new resistors to ground. Since the resistors in question are
25 all 0402 surface mount parts, this is a royal pain... but with my finest
26 dental-pick soldering iron tip, and working under the inspection
27 microscope, it is indeed possible.
29 Alternatively, if the ability to sense igniter continuity isn't important,
30 just leaving off R14 and R15 at least prevents the 3.3V processor from going
31 whacko due to having 5V applied to two ADC inputs!
33 I'm really impressed at how well these first two boards reflow soldered in the
34 electric skillet in my basement came out. Getting the right amount of solder
35 paste on the board is something I'm likely to get better at with practice,
36 but so far we've only had a few (very obvious during inspection) shorts to
37 clean up, and a couple poorly soldered pins. All in all, I couldn't be
38 happier with how this has gone... and I'm really looking forward to flying
39 one of these boards sometime soon as an auxiliarly payload to gather some