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Today's Topics:
1. Re: Loss of tracking directions after reset (Bdale Garbee)
2. Re: Loss of tracking directions after reset (Casey Barker)
3. Re: Loss of tracking directions after reset (Alex Zoghlin)
4. Re: Loss of tracking directions after reset (Bdale Garbee)
5. Re: Loss of tracking directions after reset (Bdale Garbee)
6. Re: Loss of tracking directions after reset (Jesse Frey)
----------------------------------------------------------------------
Message: 1
Date: Mon, 14 Sep 2020 18:49:13 -0600
From: Bdale Garbee <[email protected]>
To: Alex Zoghlin <[email protected]>, Altus Metrum
<[email protected]>
Subject: Re: [altusmetrum] Loss of tracking directions after reset
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
Alex Zoghlin <[email protected]> writes:
Would be interesting if people reported the e-matches and batteries they
used to see if we could understand what different combinations
might cause the brownouts in the circuit.
I don't believe these are "brownouts" in the sense you mean. It's much
more likely they're intermittent connections in wiring.
Bdale
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Message: 2
Date: Mon, 14 Sep 2020 21:35:17 -0400
From: Casey Barker <[email protected]>
To: Altus Metrum <[email protected]>
Subject: Re: [altusmetrum] Loss of tracking directions after reset
Message-ID:
<caku85pevs6rpyrcwys3bkcp5t-yegr5ofduivrcghdg7qkq...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Sorry to disagree with you, Bdale, but I feel like a "veteran" of this
"reboot at apogee" thing, having first debugged it on a TeleMetrum v1.1
back in 2011 (Wow, 9 years!), and on an EasyMini more recently.
I think in my case, it all dates back to an ancient box of J-Tek e-matches
I've been gradually burning through. After a drogue-only landing, I burned
a handful of these in bench tests and saw my TeleMetrum reset a couple of
times, so then I started testing with dead-short wires. That makes it
happen pretty regularly. I know part of the problem dates back to those
early LiPo cells with current limiters, but I've "fixed" all my cells and
can still repro.
As for solutions, I now either use a separate pyro cell or, if I can't fit
one, use different e-matches.
Casey
On Mon, Sep 14, 2020 at 8:49 PM Bdale Garbee <[email protected]> wrote:
Alex Zoghlin <[email protected]> writes:
Would be interesting if people reported the e-matches and batteries they
used to see if we could understand what different combinations
might cause the brownouts in the circuit.
I don't believe these are "brownouts" in the sense you mean. It's much
more likely they're intermittent connections in wiring.
Bdale
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Message: 3
Date: Mon, 14 Sep 2020 21:11:58 -0500
From: Alex Zoghlin <[email protected]>
To: Bdale Garbee <[email protected]>
Cc: Altus Metrum <[email protected]>
Subject: Re: [altusmetrum] Loss of tracking directions after reset
Message-ID:
<CACvQzzgbRKKkGBzgHrkq2_nQ+GRB-cDGR=j3--bbc7krq7a...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
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.
The easy answer is to always use a separate pyro circuit, but that isn't
always feasible.
On Mon, Sep 14, 2020 at 7:49 PM Bdale Garbee <[email protected]> wrote:
Alex Zoghlin <[email protected]> writes:
Would be interesting if people reported the e-matches and batteries they
used to see if we could understand what different combinations
might cause the brownouts in the circuit.
I don't believe these are "brownouts" in the sense you mean. It's much
more likely they're intermittent connections in wiring.
Bdale
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Message: 4
Date: Mon, 14 Sep 2020 22:50:11 -0600
From: Bdale Garbee <[email protected]>
To: Casey Barker <[email protected]>, Altus Metrum
<[email protected]>
Subject: Re: [altusmetrum] Loss of tracking directions after reset
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
Casey Barker <[email protected]> writes:
Sorry to disagree with you, Bdale, but I feel like a "veteran" of this
"reboot at apogee" thing, having first debugged it on a TeleMetrum v1.1
back in 2011 (Wow, 9 years!), and on an EasyMini more recently.
TeleMetrum v1 used an entirely different pyro circuit, which was indeed
susceptible to brown-outs under certain conditions. That's why we
invented the current circuit.
I think in my case, it all dates back to an ancient box of J-Tek e-matches
I've been gradually burning through. After a drogue-only landing, I burned
a handful of these in bench tests and saw my TeleMetrum
What version TeleMetrum, with what firmware revision?
Bdale
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Message: 5
Date: Mon, 14 Sep 2020 23:05:38 -0600
From: Bdale Garbee <[email protected]>
To: Alex Zoghlin <[email protected]>
Cc: Altus Metrum <[email protected]>
Subject: Re: [altusmetrum] Loss of tracking directions after reset
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
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
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Message: 6
Date: Tue, 15 Sep 2020 07:22:32 -0600
From: Jesse Frey <[email protected]>
To: Altus Metrum <[email protected]>
Subject: Re: [altusmetrum] Loss of tracking directions after reset
Message-ID:
<caf4r_macs_cjlkqrco04prslkfmndop7jhuwcddqqd1vw4t...@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
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
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[email protected]
http://lists.gag.com/mailman/listinfo/altusmetrum
------------------------------
Subject: Digest Footer
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------------------------------
End of altusmetrum Digest, Vol 105, Issue 7
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