[McHUG] Dirty Bird - Dead???

[Rich Mitchell]

Pat and I had a cell phone chat last evening about the need for a 5v reference for the pressure sensor.  That evolved to the point where a 5v reference was needed for any sensor, indicating that even thermistor readings from a dirty bird were suspect because there was no voltage regulator.  If that is the case, then any future flights of the Dirty Bird are useless in terms of gathering reliable data.

UNLESS - the voltage monitor using a diode as half of the voltage divider can give us an accurate indicator of battery voltage.  Then, though we don't have a reference voltage in the traditional sense of the word, we have a known voltage.  The voltage range we would be interested in would be from fresh voltage (6v minus the diode dropper) down to transmitter cutoff.  This might help us in at least three ways:

First:  From the spec sheets or a modeling tool like ltSpice perhaps we can calculate what the sensor measurement means for a given voltage level.

Second:  We may find that the characteristics of the coin batteries are such that they give full voltage for a long period of their life with a rapid drop off toward the end.   This would mean that a good portion of the flight would give us accurate data at a particular voltage.

Third:  If it is true that rate of rise remains constant until burst, then we only need 10 minutes of full voltage to establish the rise rate.  After that the only data we need is the sequence number - or any signal because from ground time we would know its altitude and from the sondes could know its temperature at that point.  I don't know that a Dirty Bird with party helium has a constant rise rate.

Anyway, yesterday was my last available time to build before the hamfest, so I'm out of the loop on this one.  I will try to retrofit my Dirty Bird that has the pressure sensor with the diode voltage divider for monitoring voltage.  Any suggestions as to value for the resistor to give us the best monitoring of the voltage?

Rich

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