Inside the V3.57 Board

The V3.57 board is mostly a surface-mount version of the V3.0, designed for automated assembly.  However, it has a few interesting features added to it to make it easier to configure for extra inputs and outputs.  The most obvious feature is the extra DB15 connector next to the DB9 serial port.  Three of the pins on this are taken up by ground and reference voltage outputs, leaving you with twelve new pins you can use for ignition control, water injection, or any of the features the MSnS-E and MS2/Extra codes offer.  The LEDs are no longer on the outside, although if you take the cover off, you’ll see that there are a set of tiny surface mount LEDs in approximately the same location as the LEDs on a V3.0 board.

Once you take off the cover, you’ll see the proto area is gone, but the V3.57 board now has extra pads to make it easier to access the LED outputs.  Also, the JS jumpers are no longer hiding underneath the processor socket; they’re out in the open where you can easily solder jumper wires on the top or bottom of the board.  Pulse width modulated idle control used to require adding a TIP120 transistor or similar heavy duty driver.  The V3.57 board can drive a PWM idle valve directly.  Also, the jumpers to select the ignition input are no longer soldered in; instead they are removable and easy to switch yourself.

This page will list common Megasquirt mods and how their equivalent mod works on a V3.57 board.

Ignition Input Mods

You select ignition input with removable jumpers.  The jumpers you will use are JP1 and J1.  The XG1-XG2 jumper is also a removable jumper and should normally be left in place.  Here’s how to set up those jumpers, unless application specific install notes call for a different configuration.

Tach input JP1 J1
Optoisolated – coil negative terminal 2-3 1-2
VR, Hall, or optical sensor 1-2 3-4
VR Inverted 1-2 5-6

Note that the optoisolated input was originally intended to be used for Hall effect and optical sensors, but it can run into problems with high tooth count wheels due to the heavy noise filtering needed for triggering off an ignition coil. Subsequent testing has shown the VR input works well for Hall effect and optical sensors as well.

The V3.57 board also makes it straightforward to add a 5 volt pull-up to the ignition input.  There is a pair of pads marked R57.  You just solder a 470 ohm or 1k ohm resistor (depending on what your system requires) into the R57 area and you’ve got a pull-up.

The VR trim pots look a little it different, but are still there and operate in the same manner as on a V3.0 board.