On Fri, 25 Feb 2011 23:22:03 -0800, DK Duncan <[email protected]> wrote: > Does anyone see any unknown side effects to this change? Aside from > this file, I haven't looked much further into the code.
Well, I don't think you'll really hurt anything, but there are two issues to ponder. The first is that because we're putting a very low resistance across the LiPo when firing a pyro channel, and LiPo batteries have a very low source impedance, there's a *lot* of current flowing. As long as your match actually fires and goes open in something like 150ms, you should be ok, but if somehow the match retains continuity, you're going to drain a lot of energy out of the battery and warm up some traces in 2 seconds. The second is that there's a risk of pulling the 3.3 volt rail down far enough to cause a processor reset if you keep the FET "on" with a low resistance across the pyro terminals for long enough. I put a 100uF ballast capacitor on the 3.3V rail which is on "the other side of the regulator" from the LiPo to help protect against this eventuality, and again, as long as your matches actually go open in a couple hundred milliseconds, all should be fine. But if you have a short across the pyro terminals and leave the FET on for 2 seconds, you should expect the processor to reset leaving you in a pretty seriously undefined state! When we were switched to this pyro circuit for v0.2, I did some serious bench testing with different commercial e-matches and the Quest Q2G2 igniters, and discovered that they all fired *really* fast. That's how we ended up with 50ms. > What would be very nice is to allow this value to be specified as a > parameter in a setup menu. I may look into adding that code if any one > is interested. Yes, we've talked about supporting that before. I don't think it would be hard to make that change, but we're constantly on the verge of running out of flash space. If you can make it clean and small, then I suspect Keith would accept such a patch. > Also, before making the change, I compiled the firmware and compared it > to the distributed versions. They don't match. Any ideas why? If you built from the head of the master branch, you're building our latest "unstable" code. Look for tags marking where the various release points were if you want to rebuild one of those. Bdale
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