Board Modifications

In order for the megasquirt to drive the coils, it needs a signal from the 24x crank sensor and the 1x cam sensor. The first modification is to the tach input circuit.


As you can see, cut the jumper from TachSelect to OptoIn (if you have it). Then remove the jumper between XG1 and XG2. Jump TachSelect to XG1. Remove C30 (if installed). Run a jumper from 5v (on the prototype area) to the top hole of C30. Remove the resistor at R12 and replace with a 470 ohm resistor. Make sure that OptoOut is jumpered to Tsel.

Next you need to build a similar circuit for the cam position sensor in the prototype area of the board.

It calls for a 4N25 optoisolator, but I'm using a 4N35 with no problems. Remove any jumper you may have at JS10

Next we need driver circuits for the coils. The easiest way to do that is to use the existing LED driver circuits and just add a pull-up resistor.


Simply add 3 4.7K ohm resistors to the prototype area and run 5v to each one. Run the other end of the resistor to the top side of each LED. Then run a jumper from D14 to IGN (remove any previous jumpers run to IGN), from D15 to SPR3 and D16 to SPR2. There is no need to build a SparkD output.