This application uses the Roctronics unit as a dual deployment altimeter.
This will require one controller a sensor board and a harness.
This unit is a barometric unit so the sensor board does not need an accelerometer on it.
Theory
I used information from a NAR research paper that was written by David
Schultz it was called "Barometric Apogee Detection Using the Kalman
Filter.
That paper can be found on his web page at: http://home.earthlink.net/~david.schultz/
I will work on implementing the Kalman filter into the system. This is going to be very involved. The paper also discussed using a recursive filter, and that is what I did.
First I typed in the program that he had listed in the paper so I could test some data.
I decided that adding 4bits of resolution to the 12bit ADC reading was sufficient to filter noise. I also found that a weight(sensitivity) of 1/16 was plenty to accomplish filtering of the data.
Here are two sections of a graph of data that lists the raw sensor data(this is 10bit data from an RDAS) along with filtered data using different values for filtering.
Pressure data plot
Acceleration data plot
I included the data of the Acceleration plot because I will implement this filter in the accelerometer version as well.
This data was from a hybrid flight and from the data it can be seen why there have been issues with launch detect since there are noise spikes that go below 0G.
Testing
This design was flown at Buffroc on Aug 3, 2002 in the Roctronics test vehicle.
It was also flown at that launch as the electronics for the 4pak. That flew on 4 H238 motors to over 4 thousand feet and pulled close to 30G's. And deployment was right on schedule.
Code
This is the latest sourse code for the PIC controller to control barometric dual depoyment.
