After a rather large break from building rockets I have started to start design and construction for the competition this summer. Whilst I was buying the parts to make more robinson couplings, I saw some other brass components which I thought could be used to make a working pressure switch.
The micro switch is clamped onto the two flat brass circles shown above. A balloon is held in between these two brass circles. In theory when the pressure builds up in the rocket, the balloon should expand through the hole in the brass circles and press the micro switch.
The idea is to use the parts to make a pressure switch that can just screw onto a robinson coupling as shown below.
Good news first, it works, the micro switch engages at around 15-20psi. Only problem I am having however is the classic problem of making it airtight. After about 40psi there is a notable hiss of air leaking. I will continue to work on it, using some rubber washers and sealent to try and make it air tight.