W9KE Satellite Tracker - MicroController

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The processor used in this project is a Parallax P8X32A-D40 which is the 40 pin DIP version of their Propeller chip. The chip is a 32 bit 80 MHz processor with 8 cores (cogs). It is an amazing chip with 32 I/O lines and single unit cost is currently only $7.19. Perhaps the biggest advantage to the Parallax chip is that no additional hardware of any kind is required to program the chip.

The picture below shows the microcontroller board on the left connected to the motor controller board on the right. The only other major parts on the microcontroller board are a 32K Byte serial eprom, a 5 MHz crystal (internal PLL multiplies the crystal frequency by 16 to get the 80 Mhz clock) and two voltage regulators. Each of these parts currently costs $1.50 or less. Full information on the chip as well as schematics is available on the Parallax web site.

One way to build the microcontroller board is to purchase discrete parts and use perf-board or something similar. This method is shown in the picture below. The microcontroller board is the one on the left. The board on the right is the motor control board. If you decide to build from discrete parts I suggest getting what Parallax calls the "Propeller DIP Pin Map Sticker". It is a sticker that you attach to the 40 pin chip and it shows all the pin functions. It is by far the best fifty cents you can spend on the project.

Another way to build the microcontroller board is to use one of the premade proto boards designed for the surface mount version of the Parallax chip. Parallax makes several of these boards. These boards offer several big advantages. They are smaller. A surface mount version of the processor chip is used which saves a huge amount of space. It is wired and tested - priceless. It costs only slightly more (or in some cases even less) than the discrete part solution. The 'Propeller Proto Board' shown in the picture below currently sells for $24.99 ($100 for 5 boards). If you plan on using a USB interface to your computer it is even a better value to use the 'Propeller Proto Board USB' which currently sells for $29.99 ($100 for 4 boards).

Below is a picture of a completed microcontroller board using the 'Propeller Proto Board'. It has all the components required for G-5500 control and connectors to connect to a motor control board if using stepper motors. As you can see there is not much to it.

The processor has 32 I/O lines. The table below shows the function of each of the I/O lines that are used. The last 7 lines shown in the table are used only if you are adding the G-5500 function. The Real Time Clock (I/O line 6) is used internally by the program - nothing is or should be connected to that pin. If you are building a unit from discrete parts you can find the pin numbers for each of the I/O lines in the Parallax documentation. If you are using a premade protoboard the I/O lines are silk screened on the board which is a big help when wiring. The pin numbers for the LTC1298 A/D are in the spec sheet.

Processor I/O Lines
I/O Line
Serial I/O RX
Serial I/O TX
LCD Display
Motor 1 Phase 0
Motor 1 Phase 1
Motor 1 Phase 2
Motor 1 Phase 3
Motor 2 Phase 0
Motor 2 Phase 1
Motor 2 Phase 2
Motor 2 Phase 3
Real Time Clock
LTC1298 A/D CS
LTC1298 A/D Data
G-5500 UP
G-5500 Down
G-5500 Right
G-5500 Left

Here are some pics of the completed controller mounted in a Parallax box.

For more information on various parts of the project click on the links at the top of the page.