The V3.57 is a surface-mount device (SMD) version of the MegaSquirt^® V3 'thru-hole' main board. The 3.57 version of the board was created in order to allow for automated assembly of the majority of components using automated pick and place (machine assembly) and reflow soldering (thru-hole components are harder to assemble since the leads must be inserted into rather small holes, and there's lots that can go wrong in that process. SMD also means that holes don't have to be drilled in the first place, and the SMD components are smaller and often cheaper than corresponding thru-hole components).

Although this board uses surface-mount components, the layout is the same as in the V3 main board (with the exceptions noted below). Component numbering remains the same in nearly all cases. In fact, this board version started with the V3 main board, and maintains the 4-layer construction and power distribution. It is the same size (4" x 6") and the connectors are in the same places, so it fits in the standard case with no modifications (though some modifications may be necessary for additional functionality).

Note that the V3.57 board is not a replacement for the 'build-it-yourself' boards, but rather an additional version of the MegaSquirt^® main board intended to make life easier for distributors who are building their boards for resale.

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:

• Majority of the passive devices (capacitors, resistors) and some of the active semiconductor devices (transistors, etc.) have been converted from thru-hole to surface mount. The package size for most devices is 0805 (0.080" x 0.050"), with a few 1206 and 2502 case sizes.

• Tach input selection jumper JP1 is now on 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 is for routing the signal-conditioned tach signal to the processor. 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 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 are removed and jumper wires installed in place. Also, since the LED drivers are often used for alternative output applications with the spare outputs, there is a new 1K Ohm pull-up resistor connected to the driver transistors, and this connection is available on the PAD1, PAD2, and PAD3 PCB terminals (see schematic for details).

• There is a unpopulated pull-up resistor on the tach input line (R57) 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 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 MAP sensor has been moved higher on the PCB, but still mounts underneath.

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

• The two VR input circuit potentiometers (R52 and R56) have been replaced with a 5-turn surface-mount variant.

• The processor pin jumper ports JS0 through JS12 have been brought outside of the processor and arranged in 0.100 inch spacing. There is no change in the pin/jumper name assignments, and these have the same functions as with the V3 thru-hole main board.

• The fuel pump and fast idle solenoid outputs are now driven by a power driver IC (Integrated Circuit) from ST, the VNS3NV04D. This device will drive up to 3.5 amps continuous and has a clamp voltage of 40V.

• On the fast idle output there is a diode hat minimizes power dissipation on the driver chip for PWM fast idle applications.

• The 32 KHz crystal (for MegaSquirt-I) is a surface-mount version.

The full schematics are here: hardware.htm

Surface Mount Devices

All the V3.57 main board's integrated circuits, resistors, caps, etc, are surface mount devices (SMD). The V3.57 main board uses the mostly 0805 SMD footprint for the user assembled devices, but there are also a few 1206 and 2502 sized devices.

Surface mount device (SMD) component sizes are usually stated in terms of their approximate size in either inches or millimeters. The footprint (size) of flat chips is identified by a 4-digit size code. The first two digits in the size code refer to the length, and the second two digits refer to the width.

In the USA, this 4-digit size code is measured in hundredths of an inch. Outside the USA, the size code may be either tenths of a millimeter or inches. This can cause confusion, so it is important to verify whether the size code is in metric or inches. For example, if the first two digits in the size code are 12, then the length of the flat chip is .12". However, if the size code is metric, the 12 would equal 1.2mm. For example, a ceramic SMD capacitor (or resistor) which is 0.126 inch (3.2mm) long by 0.063 (1.6mm) wide is called a "1206" size. There are numerous exceptions, however. For example, SMD tantalum capacitors are usually defined by their size in tenths of a millimeter, so a 1206 tantalum is called a 3216 (3.2 mm long by 1.6 mm wide).

Here are the most common size codes for capacitors and resistors: