🚀 go-pugleaf

donohuej@woods.ulowell.edu writes...
>	I am a hang glider pilot and would like to design an instrument
>that locates thermals (rising hot air bubbles).  I have though of using
>fast temperature sensors, one on each wing tip, and letting software
>interpret the data in real time and recomend a left or right turn.  Can this 
>be done with infra-red or any other means?  The temp difference is only a 
>few degrees at best.  It must be light weight, run on batteries, and cost 
>less than $200 if possible. An imaging system that would let you visualy
>find thermals would be ideal but I don't think it is possible with the above
>restrictions. 

Easiest and most sensitive thing I can think of is a simple 4-R bridge
with 10K thermistors. Use one on each wing tip (small twisted-pair leads
work fine) for half the bridge. Use a 20K linear-tap potentiometer for
the other half of the bridge. Use a pair of D-cell nicads or so for power
and a sensitive analog meter for a null-detector. If you want to get
fancy, use an op-amp for better null detection. Just turn the pot until
the meter shows null and go. When the needle moves left, follow it. The
small panel meters can take a fair amount of shaking/jolting if there
is some shock isolation and it's *very* readable in daylight.

Thermistors usually have several ohms per degree change (sensitive) and
don't usually need amplifiers or special connectors/wire like thermocouples.
They are also about a buck, so order several for future projects... - jim
-- 
James Wyatt  KA5VJL  jim@rwsys.lonestar.org  Semper Gumbi - always flexible!