I started with a design from Jerry Baumeister and modified it to beep the altitude in feet automaticly after it gets close to the ground. I also used some deployment plans from Bernard Willaert in Belgium. I had the electronics part finished and destroyed it when the parachute was not packed properly, and pushed the door open on liftoff.
A little explanation about how it works.
Pressure readings are taken with a barometric pressure sensor.
The PIC 12F675 micro controller converts the analog reading to digital
number and says that it is the zero reading. Every time that it sees
a pressure that is lower, it updates the maximum height reading.
Then if the pressure starts to increase and it has gone above 90 feet then
it triggers the mosfet "switch". This discharges the capacitor across
a solenoid. A magnet that holds the door hatch closed is attracted
to the solenoid but durring the discharge phase the solenoid repels the
magnet and the door flys open. Hopefully the parachute opens afterward
and the rocket falls gently to your awaiting hands. When the rocket
gets below 60 feet, it starts beeping the maximum altitude. That
way if it lands in high grass or in a cornfield you can follow the beeping
noise to track it down.
Keep in mind it has never been calibrated, so I don't know how accurate
it is.
I would like to take out the high voltage part of the circuit and
replace it with a geared micro motor (from a pager) to open the door but
I have not got around to it yet. Here is a
good source for the motor only $1.19
OK, funny story....
To test it out the assembly, I charged the capacitor to ~300V. Then I turned on the switch and listened to it initialize and take it's zero reading. Now in order to simulate the travel to a higher altitude, I had to decrease the pressure on the barometric sensor. How did I do that you ask? Well while it was still in my proto/experimenters board, I had tube connected to the sensor and I sucked on it with my mouth. Easy enough right. Well, I had cut the part off that held the tube to save a little weight. Right, so what I did next was "brilliant". I put my lips up to the sensor itself and was going to inhale lightly. Instead, I exhaled loud profanity as three hundred volts past to my lips and thumb. POW!!!
I forgot to flip my circuit board transfer before ironing it on, so the PIC micro controller is on the wrong side. Oh well, it works this way too.
Here you can see it mounted into the nose cone/payload area.
The parachute is from a pink anti-static bag that the electronic parts
were shipped in.
I think this is a nice shot of the door just opening. If you
look closely you may see that the parachute is being pushed out by a clear
plastic "spring"
Start with Jerry Baumeister's part list
>
You will also need
one IRF740PBF 400V Hexfet
three 1N4007 Diodes
another 0.1uF Capacitor
another 1K ohm resistor
one small piezo buzzer
one 300V capacitor from a one time use flash camera
one 12V Relay/solenoid
one strong small magnet
The part number for the piezo buzzer is obo-13240pa
mouser's part number is 254-PB507
it is really light and small, about 12mm in diameter.
You will have to right click on the link and select save