Archive for December, 2008

Pressure Switch – Part 2

Saturday, December 20th, 2008

I am having a real hard time getting the pressure switch to be fully air tight. The switch works, but after 20-30 seconds, it stops conducting. I am guessing that there is some tiny air leak which is letting in undetecable amounts of air. I have been unsuccessful in sealing the switch any further.

I will continue to explore ways of making a more sealed switch, but I am also looking into other ways of detecting the end of the booster thrust phase.

  • Pressure – Similar to the current switch I am working on, but with a small switch inside a balloon
  • Temperature – According to Boyle’s law as pressure drops, so should the temperature if the volume of the bottle stays the same. A thermistor should be able to detect this.
  • Water Sensor – Detects when all the water has been expelled from the rocket.

Pressure Switch

Sunday, December 7th, 2008

I have been working on a pressure switch which will be an essential part of our multi stage rocket next year. The idea came from Air Command Rockets.

The pressure switch is made from a old TV remote control button. The membrane and the circuit of a single button are sandwiched in between to small metal plates. This in theory should seal the air inside the rubber button. This is then placed inside the pressure chamber.

As the pressure chamber is pressurised, the air pressure forces the button to be pressed and hopefully presses the contacts on the circuit board. When the rocket launches, the pressure will fall and the button will depress, disconnecting the circuit. A circuit will look for the switch disconnecting and will then trigger the staging mechanism. I am hoping to test this soon and will report findings.

PIC Chip Programmer

Monday, December 1st, 2008
Velleman 8048

Velleman 8048

I’ve gone and bought myself a PIC Chip programmer to play about with. Its the Velleman 8048 kit and comes with a 16F627 PIC.

I am intending to hopefully use a PIC Chip to replace the two chips used in the current Optoelectronic Apogee detector circuit.The supplied PIC has both a onboard comparator and Pulse width modulation on some of the outputs, meaning that only a handful of external components will be needed to construct the circuit from now on.

Once I have that working, I can then hopefully change the code to introduce failsafe features to release the parachute after a certain time period, in case the circuit fails to detect the rotation of the rocket. However I have never used PIC chips before both on the electronic and the programming side so it will be an intresting journey. I will report my findings as I go.