Bdale, Thanks for the description of the circuit. I had seen all these things in the schematic but never really put it together to understand how they came together to prevent brownouts. I will remind everyone that, as I said in the original e-mail, my AV-bay came apart so, this is a likely cause of a reset (actually I'm a little surprised that it came back on). I never meant to suggest that the TeleMetrum was at fault merely I was curious as to why I could not track it on the way down. After looking closer at the data (that I attached in the first e-mail) it appears that the GPS lost lock in the reset and did not regain it on the way down. Jesse
On Mon, Sep 14, 2020 at 11:05 PM Bdale Garbee <[email protected]> wrote: > > Alex Zoghlin <[email protected]> writes: > > > I was going to respond and say this is something that is pretty easy to > > test, but I think Casey beat me to the punch with a bit of empirical > > evidence. If you look at the RRC2/3 series altimeters, they contain a big > > capacitor specifically to continue to provide power in the case of a > > brownout that used to happen on their old altimeters when the right > > combination of ematch and battery created an extreme short that exceeded > > the batteries limits, including 9 volt batteries. > > Big electrolytic capacitors are a mechanical disaster, and a potential > point of failure in and of themselves. > > So the "more cleverer" solution we came up with years ago and use on > everything now is to put a diode and relatively small ceramic bulk > capacitor in front of the LDO. This allows the LDO to ride through short > interruptions. Then we use a comparator to watch the voltage at the LDO > input, and when the cap has discharged to the point where the LDO output > will soon start to droop, the comparator briefly disables the pyro channel. > That "removes the short", the bulk cap rapidly recharges, and then the > comparator allows the pyro channel to turn back on. > > The idea is that we're putting as much energy into the pyro device as we > can without ever allowing for the possibility of a brownout, until the > battery is fully discharged. We choose the size of the bulk cap to > ensure a pyro channel with a dead short will see well over 90% "on" duty > cycle. With a normal e-match, the match will fire in the first "pulse" > well before the comparator trips in, so all of this is irrelevant. An > upper-stage igniter or something that needs more joules can get them > across multiple "pulses" from the pyro circuit. > > This is why I don't think the effect being seen is a "brownout" in the > traditional sense. > > It's certainly true that a separate pyro battery means this circuit will > never become part of the equation. However, separate pyro batteries > also add complexity and more potential points of failure. There are no > free lunches here... > > And, of course, it's always possible there's something going on we just > don't understand yet. If you think so, please please please quote the > hardware and firmware version so we don't waste time and can get right > to thinking about possible explanations. > > Regards, > > Bdale > _______________________________________________ > altusmetrum mailing list > [email protected] > http://lists.gag.com/mailman/listinfo/altusmetrum _______________________________________________ altusmetrum mailing list [email protected] http://lists.gag.com/mailman/listinfo/altusmetrum
