My Rocket Controller

This is my design for a rocket altimeter.

I wanted to build a more advanced altimeter than my stamp based altimeter.

Requirements:

These are some of the things I wanted out of my altimeter.

1) To sense pressure and acceleration.
2) Measure with 16 bits.
3) Control and download using infrared(Including arming).
4) 3 output channels. Main, drogue, and airstart or camera.
5) Capable of measuring its own battery voltage.
6) Ignitor/ejection charge measurement(not just continuity, good/bad).
7) Minimal/No mechanical switches.
8) Capable of using dual power sources.
9) Auxiliary interrupt driven input for camera photo sense.
10) Large storage for the 16bit data at a high sample rate.

The circuit:

schematic here

As you can see I wanted more than an altimeter. I wanted a flight controller.

If you see anything that could be improved, please, let me know.

I started off the design with the PIC16f84. This is the brains of the outfit and because I have yet to finish the design I hope it can do all I am asking of it. I picked this chip because I have a programmer that will program it. Also it is very versatile and user friendly.
I decided to go with the 24LC256 eeprom because it was the biggest one I could find. It was a very scientific scan of the available parts and looking for the biggest one currently available. Even with that I only found 1 vendor with stock of the surface mount version of this chip.

To this I added the ADS8344. This is a 16 bit analog-to-digital converter. It has a built in multiplexer that will handle 8 inputs.
It is fast enough so I can get the 200 sps(100 from each of the sensors) that I want. Because the ADC has an interrupt output to tell the controller that the conversion is done it makes programming easier.

By default for the sensors I used the MPX4115 and the ADXL150. Both of these are commonly used for rocketry electronics. Theoretically using 16bits I can resolve about half a foot with the pressure sensor. Factor in noise and I would be happy with 15 feet. The accelerometer can resolve to .001g with 16 bits. Here again adding up the noise I would be happy to get .1g.

Having the higher accuracy ADC will make the data really interesting. Especially considering that most of my rockets fly under 2000ft. With that low a ceiling the 12bit data from my other altimeter was really crunchy. Especially if it was only a 500ft flight.

On to the unique part. I found this little chip the CS8130. This chip takes a standard RS232 serial input signal and converts it to IrDA compliant infrared signals that can communicate with just about any laptop or Palm PC. As for the palm pilot, I don’t know if it uses any "standards" besides I need something with capabilities.

Operation:

The IR port will allow me to communicate from my Pocket PC to the rocket for setup and arming. I will devise my own protocol for negotiating between them. This way I can download the data and reconfigure the computer without opening the electronics bay, gee I can even check the battery status.

I will be able to interface to my camera for taking pictures using the AUX output channel and the AUX input channel. The output will tell the camera to take pictures. The input will be used as feedback to know exactly when the shutter opened and mark that altitude as having a picture. This way I can know the altitude of each picture just like on my old design.

I will modify the flight view software that I wrote for my Pocket PC so it will control the rocket and also use the IR port.

This is a screen dump of the current software

Hosted by www.Geocities.ws