Daughter Board
For MegaSquirt V2.2
Last updated 2007-09-18 11:13 PDT

Description and Features

Note that this board is as-yet untested! If you make one, let me know how it works out.

I've designed a daughter board for MegaSquirt Version 2.2 hardware. It provides IO expansion by adding two more ADC inputs, two binary inputs/interrupts and two high-current FET outputs.

  1. The board's H1 and H2 headers plug right into MS V2.2 boards when the appropriate header pins are added to the MS board's already existing holes. I think it will fit in the MS case on top, and may even fit in below it if you're careful.

  2. It only requires two surgical implants on the MS board, one to grab Vref for the ADC circuits, and another to get +12 power for the FET driver. All other connections are through the headers.

  3. It uses a copy of MS V2.2's injector driver circuit and connects it to PTA2 (pin 35/X5) and PTA3 (pin 36/X4). Each FET can be used to drive an idle air controller, a boost control solenoid, high-impedance injectors, air conditioning relays, or whatever you like.

  4. It adds another pair of thermistor input circuits to AD6 and AD7. Stick another couple MAT sensors on either side of your intercooler or turbo and then calculate efficiencies. I might put another MAP sensor circuit as a jumpered option, then you could do either continuous barometric correction or measure exhaust back pressure or you dream up something.

  5. It also adds a pair of input interrupt lines to KBD6 and KBD7. They could be used for VSS or ABS sensors or something. Applications might include traction control or a turbo tachometer. These inputs can also be configured as simple binary inputs, polled whenever you like rather than interrupt drivers (that's all software).


You can see the heatsink (0.0625"x1"x4" aluminum) and the globs of silicone used to hold the tall parts and parts with long legs. The heat sink can be see to slide into one of the enclosure slots and is bolted to the tabs of the FETs). I have it mounted on top of the MS because the stock enclosure doesn't have a slot in the right place to hold the board on the bottom. If the enclosure had one more slot, it would fit on the bottom just fine.

C6 and C8 are not installed on this one (I ran out of parts), but all the other parts are there. Once I've located a place to drill some 1/8" holes for standoffs, I'll modify the board layout and provide instructions for drilling the MS board. One concern that I have is that the top-mount location will block access to the SPI and interfere with MJ/MJL installations.

Bottom of board. You can see the 0.100" header pins that plug into the connectors on the MS board.

Connections on MegaSquirt. Note two things: 1) the components around the clock circuit are all layed out flat on the board for clearance; 2) the 2-pin and 6-pin connectors just to the left of the MCU that accept the pins from the bottom view, at left.

  • The image to the left is about actual size (2.5"x3.8") depending on your screen size. Click the image for a bigger gif.

  • Schematic in a big gif.

  • PostScript version of schematic suitable for printing on 8.5x11 or A4 paper.

  • Silkscreen for top of board.

  • PCB Layout in ExpressPCB's format.
    Schematic in ExpressPCB's format.

    Go to ExpressPCB for software to view the above files on a Windows box, and pricing on boards. (No affiliation, not even a satisfied customer; just got a couple recommendations from list members.)

  • DigiKey BOM Bill of materials order form.

Not2Fast hosted by TrackFiends