From: Bdale Garbee Date: Fri, 27 Mar 2009 08:30:45 +0000 (-0600) Subject: tell the world that TeleMetrum works! X-Git-Url: https://git.gag.com/?p=web%2Fgag.com;a=commitdiff_plain;h=6eaa41bffcab4c37b49a1e0bf490e2c5608a8610 tell the world that TeleMetrum works! --- diff --git a/bdale/blog/posts/TeleMetrum_Working.mdwn b/bdale/blog/posts/TeleMetrum_Working.mdwn new file mode 100644 index 0000000..5d1643e --- /dev/null +++ b/bdale/blog/posts/TeleMetrum_Working.mdwn @@ -0,0 +1,40 @@ +[[!tag tags/rockets]] +Keith and I have been plugging away for the last couple weeks +turning on and testing the various +bits of [TeleMetrum](http://altusmetrum.org/TeleMetrum), +and I can now very happily report that we have all the hardware +working! Amazingly, we got almost everything right in the +hardware design. Only two things need to be changed. + +We need to be able to control the chip select line on the the SPI +non-volatile memory chip, which means we need one more GPIO line to it +from the processor. To free up a line, we gave up the ability to put +the accelerometer in to self test mode. Two trace cuts and two jumpers +to the current board implement this change. + +The last thing we got working just this evening was the ability to sense +the presence of an ejection charge igniter. We need another resistor in +each of the two sense circuits to form a voltage divider so that we don't +overload the ADC input. Not sure how we missed that in our many design +reviews! Oh well. To ensure robust ignition of the electric matches +we prefer to use for ejection charges, we charge a 1000uF cap to a voltage +higher than our ADC inputs can handle. Fixing this problem on the current +boards requires changing the values of two resistors, then tacking extra +resistor to one end of each of the existing ones and then wiring the other +ends of the new resistors to ground. Since the resistors in question are +all 0402 surface mount parts, this is a royal pain... but with my finest +dental-pick soldering iron tip, and working under the inspection +microscope, it is indeed possible. + +Alternatively, if the ability to sense igniter continuity isn't important, +just leaving off R14 and R15 at least prevents the 3.3V processor from going +whacko due to having 5V applied to two ADC inputs! + +I'm really impressed at how well these first two boards reflow soldered in the +electric skillet in my basement came out. Getting the right amount of solder +paste on the board is something I'm likely to get better at with practice, +but so far we've only had a few (very obvious during inspection) shorts to +clean up, and a couple poorly soldered pins. All in all, I couldn't be +happier with how this has gone... and I'm really looking forward to flying +one of these boards sometime soon as an auxiliarly payload to gather some +initial flight data!