[altusmetrum] TeleMetrum In-Flight Reset

[Keith Packard]

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On Mon, 13 Feb 2012 21:14:49 -0800, Casey Barker <casey at barkerzone.com> wrote:

> The TeleMetrum was configured for a 2-second apogee delay and did fire a
> Rouse-Tech CD3 (CO2 cartridge) for drogue.  I think the use of the CD3 is
> why there's not much of a bump.  The Raven was set for 4 seconds and
> connected to a BP squib.  I know the Raven blew after the TeleMetrum
> because there was no BP residue inside the airframe (unlike for the
> main).

Ah, all is clear now -- the 2 second delay was internal to the TM. The
TM reset just under two seconds after apogee. (apogee at +27.68s, last
data at 29.49s). TM would have sent a couple of packets past apogee
indicating drogue state; perhaps they were just lost?

> For what it's worth, on my first flight of this unit, I misconfigured the
> Raven and it fired the drogue BP a couple seconds early.  In that flight, I
> saw a clear pressure spike in the TeleMetrum data when the Raven blew the
> drogue, and later, the TeleMetrum successfully fired the main CD3 with no
> apparent bump.  (It then reset immediately after deploying main.)  So it
> seems like a similar issue as last time, but just reversed
> drogue/main.

Yeah, it's like your board doesn't have the fix installed; once we stuck
a cap across the LDO input, we couldn't cause *any* kind of voltage drop
on the 3.3V rail.

> I don't think this is it, based on the above description.  But I have gone
> through the Raven's flight cycle on the bench, and it doesn't seem to
> interact with the TeleMetrum.  I was actually thinking that a feature
> similar to the Raven's "simulated flight" would be really useful on the
> TeleMetrum.

I've thought about this. I coded up bits of it a few months ago; of
course, it would require talking to the TM board over USB, which makes
it less than ideal from an electrical perspective.

> Being able to fire charges on demand is oh so helpful (more
> useful than the Raven, frankly), but it doesn't properly simulate the
> combination of firing charges and tx'ing live telemetry.  I think that's
> where the issue lies.  I've poked around the TeleMetrum code, but I don't
> know it well enough to add this feature myself yet, and I'm not sure
> there's room for it.

Yeah, it's always a tight squeeze to add anything to the TM code.

> In short, it's all #20 stranded copper wire, with a tight twist in all the
> leads to switches and igniters based on the RFI lessons learned in my 54mm
> Little Dog.  The wiring harness uses the 4-pin 3M connectors and the rotary
> voltage switches from the Altus Metrum site.  All of the wiring is
> completely independent from the Raven, and the Raven is on the opposite
> edge of the bay, as far away as it can be in a 5" airframe.  I'll send
> photos in the next day or two.

Sounds really clean. Let's see if Bdale has any other suggestions on how
to test stuff; if I had the board in hand, I'd hook up a meter to the
3.3V rail and then take a high power transmitter (like a regular HT) and
see if I could get it to drop at all by holding it near sensitive bits
of the TM. That's how we diagnosed the missing capacitor issue...

-keith