MegaSquirt Expansion Board Assembly Guide

Assembly Notes

1) Unlike the MS main board where 1 size fits all (almost) the EXP board requires a bit of thought for what and how you will use it. Since the input buffers are not connected to the processor I/O lines you need to decide which buffer will be connected to which processor pin according to the function assigned that pin in the s/w. Likewise the processor output pins ( assign in s/w) are not tied to a particular output transistor. The input/output buffers are connected to the processor pin using discrete wire jumpers. Both the processor and i/o buffer pins are brought to a thru hole header holes. So by soldering a wire jumper to the i/o buffer header hole and chosen processor pin header hole the connection is made complete.

2) The output transistor can be configured as a current source (non-inverting or emitter follower mode) or current sink ( inverting mode) depending on which resistors are installed, and if the output connector pin is connected to the emitter or collector respectively. The output transistors can drive a 100ma load (non-inductive), if you need to drive a large load then you will need to hook the EXP output to an external power transistor. Inverting mode is how the LED's are driven on the MS main board for example.

3) Once you have decide how many I/O channels you wish to used I suggest that you print off the BOM and schematic. By previously selecting which input and output channels it is possible by cross referencing the parts list to the schematic and then reduce the posted BOM qty's to only those parts you require. In short you do not have to populate the entire board to make it effective.

Assembly Instructions

  1. Mount all the surface mount resistors and cap's first.

  2. Mount the output transistors next

  3. Mount the diodes

  4. Install the RS232 chip

  5. Install the 40 pin HC908 on the bottom of the board

  6. Install the 40 pin wire wrap socket through the board from the top.

  7. Once the wire wrap socket is installed, solder the adapter socket to the bottom of the 40 pin wire wrap socket. The reason for the adapter socket is that the wire wrap pins are a bit to big to fit easily in the MS main board socket.

  8. Install the miniature plug (head phone socket)

  9. Install the 6 pin dip sockets if you are using the opto-isolated inputs.

  10. Install the wire jumpers to connect the processor to the desired I/O buffer channels.

  11. Install the input and output connectors.

Testing

  1. Remove the processor from the MS main board. Do not install the either the slave (on the bottom of the MSexp board) or the primary processors yet.

  2. Plug the EXP into the MS main board

  3. Apply power and verify that you have 5v at the correct processor pins (use the schematic)

  4. Using a DVM and a wire jumper test the desired output channels one at a time.

  5. Connect +5 to each base resistor ( processor side) one at a time and verify that the corresponding output pins behaves as expected ( the action will depend on how you have configured the buffer transistor). To test an current sink output connect your meter between +5 and the output header, you should get 5V or close to it when the test jumper is connected to the processor side of the base resistor. To test a current source resistor connect a DVM between ground and the output pin, when you connect +5 to the processor side of the base resistor you should get +5 on the meter.

  6. To test the opto isolated inputs connect a test jumper to +12, connect pin 10 of the input header to gnd, using a DVM connect the DVM between +5 and the opto isolated output you are testing, when +12 is applied to the header input pin the meter should read +5.

  7. Power down and plug the '908 into the upside down socket and repower. Using MegaTune and your serial cable test the comm's to the '908 processor. Install your MS2 plug in module into the top 40 pin DIP socket.

  8. Connect the Input and output connector according to your application.
ENJOY!

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