On Sunday, January 6, 2019 at 12:14:34 AM UTC-8, bumper wrote:
On Saturday, January 5, 2019 at 7:16:12 AM UTC-8, Dan Marotta wrote:
.

The Peregrine switch is outrageously expensive (about $180) for what you
get, and with some shopping, you might find a suitable alternative,
especially in an Experimental glider.Â* After all, it's a simple pressure
operated On/Off switch.Â* One wire runs from the transponder to the
switch to ground.


Here's one source for an inexpensive ($24) and small "water column range" pressure switch. The MDA-011 should work fine (I'm using a similar switch to run a Hobbs meter to show actual flight time. Another is being used to monitor the cooling air to an engine.

http://www.dwyer-inst.com/Product/Pr...ches/SeriesMDA

bumper

I think you need a differential pressure switch to avoid the problem of changing pressure with altitude. This one appears to have only one input.