The V3.57 main board has the same mostly the same circuits and components locations as the V3 main board described here: V3 Main board introduction / assembly. The V3 assembly instructions can be used in most cases (except for the SMD devices and different soldering techniques, etc.).

Functionally, the V3.57 board operates identically to the V3 main board with only minor alterations for additional support and functionality.

The differences on the V3.57 board (compared to the V3 thru-hole main board) are:

• Tach input selection jumper JP1 (near the copyright notice at the DB-37 end of the board) is now on a 3-position standard 0.100 inch header:
  • Placing a jumper across positions 1 and 2 enables the variable reluctance (VR) circuit.
  • Placing a jumper across positions 2 and 3 enables opto-isolator ("Hall") tach input.

• Tach selection jumper J1 (near the center of the board, but a bit closer to the heat sink) is for routing the signal-conditioned tach signal to the processor. This is a 3x2 0.100 inch header. Only one jumper is used, the remaining positions are open.
  • A jumper on pins 1 - 2 enables the opto-isolator.
  • A jumper on pins 3 - 4 enables VR (variable reluctor) operation (non-inverted).
  • A jumper on pins 5 - 6 is for an inverted VR signal.

• The three front-panel LEDs - D14, D15, D16 - have been converted to surface mount devices. These cannot be easily viewed through the standard LED end-panel holes, but are easily visible with the case lid off. If front-panel LEDs are desired then the surface mount units should be removed and jumper wires installed in their place. Also, since the LED drivers are often used for alternative output applications with the spare outputs, there is a new 5 Volt pull-up with a 1K Ohm resistor (limits the current to ~5 milliamps) connected to each of the driver transistors. The added resistors are:
  • R58 for D14,
  • R59 for D15,
  • R60 for D16
  and the connection to the LED driver transistor is available on:
  • PAD1 for D14,
  • PAD2 for D15, and
  • PAD3 for D16
  (See schematics for details.)

• There is a unpopulated pull-up resistor on the tach input line (R57 - near the copyright notice at the DB-37 end of the board)) that can be added to provide bias for Hall sensor and other input sources.

• The prototype area has not been implemented on the V3.57 board. Instead there is an unpopulated DB-15 PCB-mount socket (at the same end of the case as the DB-9), with the signals brought out to a series of pads (on 0.100 inch centers). The DB-15 pins are:

  Pin	Pad
  1	Dedicated Ground (no pad)
  2	Dedicated Ground (no pad)
  3	Pad 15
  4	Pad 13
  5	Pad 11
  6	Pad 9
  7	Pad 7
  8	VCC (no pad)
  9	Pad 17
  10	Pad 16
  11	Pad 14
  12	Pad 12
  13	Pad 10
  14	Pad 8
  15	Pad 6

  Note that the pads are numbered pad6...pad17, pad20. Pad20 is a dedicated 12 Volt supply (taken after the D10 diode, and electrically equivalent to S12C that is used for the IAC).

  The DB-15 socket is provided to allow I/O connector expansion (it will also require a custom end-plate with an additional cut-out for the DB-15). There are also additional mounting holes located in this area to allow the use of custom expansion boards.

• The MPX4250AP MAP sensor has been moved higher on the PCB, but still mounts underneath.

• The output of the optional ignition driver IGBT (VB921) ignition driver is hard-connected to pin 36 on the DB-37 connector. No jumpers are required (unlike the V3 main board).

• The two VR input circuit potentiometers (R52 and R56) have been replaced with a 5-turn surface-mount variant. So instead of 25 turns, only 5 turns are required - but they should still be fully counterclockwise to start tuning.

• The processor pin jumper ports JS0 through JS12 have been brought outside of the processor and arranged as jumper holes with 0.100 inch spacing (so a standard 'molex' header and connectors, etc. can be used). JS0 to JS6 are on the DB-9/DB-15 side of the 40-pin socket, and JS7 to JS12 are on the DB-37 side of the 40-pin socket. There is no change in the pin/jumper name assignments, and these jumper locations have the same functions as with the V3 thru-hole main board.

• The 32 KHz crystal (for MegaSquirt-I) is a surface-mount version, not the small cylindrical 'can' used in the thru-hole board.

The schematics are here: hardware.htm