Altimeter

 
Rocket  . . Tiny Altimeter . . Launcher . . FTC rocket . . Build your own .
Back in 2007 I had been working on an altimeter that would record maximum altitude  in feet, then deploy the chute after apogee. It had a beeper to tell you the altitude.
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 had a request to change my code so that the guy could track the altitude of a Falcon.  You can read about it on my Tiny Altimeter page.

I did eventually take out the high voltage part of the system and put in a tiny 3 gram hobby servo.  It worked great 4 times... On the fifth launch, the battery became temporarily disconnected, causing a failure and demolished my work.  I have never rebuilt it and wonder if I ever will. Although, I have considered revamping the whole thing.  I would start with an Arduino mini board and add on a BMP180 pressure sensor.  The BMP180 has much better resolution.  I would stick with a hobby servo to release the door.  I also would still want a beeper so I could follow the beeping noise to find a lost rocket.  I also think I would 3D print a rocket module to house the electronics, battery, and parachute.  That way, I could easily print a new one if it needed a change or if there was some catastrophic failure. (A crash).  --- Just a note: Some would argue that I should use an ATtiny85 to save weight and space... maybe I will someday.
 
 

Here is the circuit board with all the stuff on it.  You can almost read the print on the capacitor.  Yep that says, 330V. 
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"

Picture of circuits (click on the picture to see a larger one.)

Parts list 
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 also need to make a 300 volt charger from a one time use camera.  Follow Bernard Willaert's directions for this.
.ASM code is here
You will have to right click on the link and select save 
 
 

  I used Bruce Berggren's launcher design (dead link)

Tim Sumrall has some good ideas (dead link)

Jon Mehlferber has a way to thermoform bulkheads for FTC rockets


 
 
 
 
 

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