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Flight Computer

My flight computer uses the PIC 16C84 CPU, clocked variously between 4 MHz and 16 MHz. It is powered by Lithium watch batteries. The PIC 16C84 was chosen because it is a RISC proccessor with only 35 instructions (it is blindingly fast - about 1 million instructions per second per 4 MHz - as well as straight-forward to code), and also because alone amongst the PIC 16xx CPU's, it has onboard EEPROM (electrically erasable) for program storage (1K words) and data storage (64 bytes). The Flight computer is also equipped with a 8Kb external EEPROM (in an 8 pin package) which can be used for onboard data storage. The Flight Computer interfaces to any number of sensors (altitude, accelerometer, etc), but is not as capable as Jim Macfarlane's superb PIC flight computer for use as a pre-proccessor in the AspireSpace rockets.

The 16 pin PIC 16C84 CPU also uses the SPI bus, a really neat 2 wire bus. Through this, you then just hook up all your sensors.

There is also a SOIC (i.e. surface mount) version of the PIC 16C84, which allows you to make the circuit even smaller. (Programming is by means of 2 pins, so on the surface mount version, it is useful to have two PCB pins fitted on the circuit board for this purpose, or even small connector pins, which can be plugged into a connector). Although the surface mount version of the PIC makes for a really small PCB, it must be borne in mind that the Flight Computer circuit board is already quite small (3.5 inches long x 1.7 inches wide).

Flight Computer Information

CPU : PIC 16C84
Package : 18 Pin DIL or SOIC
Clock Speed : 4 - 16 MHz
Power : 2 x 3 Volt Lithium Watch Batteries
PCB Length : 3.5 inches
PCB Width : 1.7 inches

The other beauty of the PIC, is the ease with which it is possible to program it from a PC. It costs less than 5 to build a programmer, which can then be plugged into the serial port of any PC by means of a D-plug. The code can be developed on the PC and then downloaded to a PIC 16C84 placed in the programming socket on the PIC programmer. The PIC 16C84 is then removed from the programmer and then placed in the circuit in which it has been designed to work for.

Copyright 1996-1999 Richard Osborne, All Rights Reserved.