Hi Tim,

> How did you get hold of a radiosonde.  If you found it you are supposed to
> return them!

You can buy, beg or find them quite legitemately.  Those found have
no real value besides possibly the location they were found at and if you
actually find the specific site that launched the sonde they will be
interested in the location and the time you found it, possibly serial number
but they may not keep records of them.

These devices are sold for about US$ 50 and are single use.  I have a
few in my collection (4 types) and none of them actually indicate they
might be wanted back.  The one that Electronics Goldmine sells Which has
SDC Presure sensor has on the printed box the statement :

   "This instrument can be safely discarded into any trash receptacle"

Also other statements to the effect that it wont explode &c.

There are other makes that are available but no others that I know
of on the surplus market.

> >     I would appreciate any information anyone might have on using the
> >     pressure sensors found on the Radiosonde weather balloon circuit
> >     boards, they are in a metal can - 8 lead package with the following
> >     marking:   SDC 909-4502803 07

It will be a silicon resistive strain bridge measuring absolute pressure
(rear side of diaphragm at vacuume) and one would be best served by
tracing the circuit of the sonde to find out how it is used.  The
circuit first generates a voltage from the pressure transducer and then
selects one of 6 voltages (pressure, temp, humidity, ?, HIref, LOref)
and feeds it into a V-to-F converter which is then used to modulate
the radio section which is almost so simple that it does not look like
it can be a transmitter (one transistor and a Teflon spaced tuner
capacitor with a 1/4 wave groundplane antenna).

Problems with the sensors and the circuit in the sondes is that they
are not made for long term stability and are reference callibreated
on the ground at the time of launch.  For Rocket use this should not
be much of a problem but for long term climate studies I would
hesitate to trust the stability without carefull characterisation.

Interfacing to a Stamp or PIC might be possible to do with just one
arm of the  bridge in resitive mode for Rocket applications as the
time is so short there will not be much temperature drift.  Otherwise
you will need to put in a bridge amplifier and then amplify result
to feed a A/D or V/F converter.  It was relatively easy to get the
sonde board to generate a single freguency by bypassing the MUX
chip and feeding the pressure output directly to the V/F converter
and then one could use that output to feed a FREQIN or something
on a Stamp or PIC.  The Audio tone at about 1.2kHz or something
gets real irritating after a while when playing with it and in the
end you just stick to the scope and F-counter even though audio is
a faster way to detect changes.

Cheers
--
Kalle Pihlajasaari   kalle@ip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer