Common MegaSquirt Modifications

Adding a second wideband o2 sensor to the MegaSquirt-II

Adding an relay control circuit to the MegaSquirt PCB-3

Adding a 'Pullup Resistor' to the ignition input

Adding a second wideband o2 sensor to the MegaSquirt-II

This requires a pretty minor mod.  You’d need to duplicate the o2 input circuit on the main o2 input, it’s only 3 components and could easily be built on the proto area of the v3 PCB. The Input is labeled ‘O2’ below and could go to ‘Jmp SPR1’ on the PCB which would bring it out to pin3 so you could wire the o2 sensor there. The output to the MS2 CPU is labeled ‘AD5-1’ below and would be routed to ‘JS5’ on the PCB which would route it to the proper pin on the CPU. That should be all it takes.

Adding an relay control circuit to the MegaSquirt PCB-3

Great for Megaquirt-I, PCB3 units with MSnS_E code.  For MS-II units with firmware version 2.3 or later you don't need to mod anything!  Use the FIDLE output on pin 30!  See http://www.megasquirt.info/ms2/spare.htm for more information on the MS-II outputs.

This is one example of what you can do, in this example I used the JS3 output from the MS-II CPU as the input into this circuit (telling it when to switch on/off) and the output routes to Jmp SPR1 which sends the signal out to the DB37 on pin3 which is a pretty good choice since on the v3 it's not used for anything else.  You'd then use pin3 on the DB37 to control your relay which controls your electronic doodad of choice ---  shift light?  electronic fan?  variable intake system such as Toyota TVIS?  Honda VTEC?  EZ Bake Oven?  Whatever you want....    

Here's pictures on this mod performed on the V3 board, click for a close up view.  (Red wires are this mod, ignore the white)

Adding a 'Pullup Resistor' to the ignition input

PCBv3.0 Boards, MS-I or MS-II

A 1k (1000 ohms) 1/4 watt resistor is what you want.

Solder one end to the right side (non-band) end of D1, and solder a small piece of wire to the other end, heatshrink tube the resistor and solder joint to protect it, and solder the other end of the wire to the leg leg (banded end) of D9. The left/right references are when looking down at the top of the board so that you can normally read the text, though you will probably do this mod on the bottom of the PCB...


Alternately... you can do this in your harness. Use the same resistor, hook one leg up to the wire connected to pin 24 (inner conductor only if you're using shielded wire) and hook the other end up to a 12v source, like the wire connected to pin 28, the main MS power wire.  This harness method works for PCB2.2 or PCB3.0 boards.  Heatshrink tube everything up nicely to protect your wiring, and maybe tape this resistor up in the wiring to keep it from getting bent up alot as you don't want that connection to break, and the resistor leads could get brittle if they get bent much.

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