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Friday, November 25, 2005


Introduction to Megasquirt

Here's something I wrote for all the people who show up on the Megasquirt Message Board and want to know what version or kit they need to buy.

Megasquirt's versatility can sometimes seem intimidating to a beginner. If you're confused by which version to order or what you need, you're not alone. Here is a brief explanation of the many Megasquirt versions, along with other devices you may wish to order to make installation easier. The MegaManual provides more details about each version, along with directions for how to install and tune the Megasquirt. This manual is essential to completing an installation, but hopefully this little essay will help you get an idea of where to begin.

The Megasquirt unit itself can be considered in three key parts: The processor, the main board, and the firmware. The processor is essentially a self-contained computer, with its own memory as well as the ability to run software. The main board connects the processor to the outside world and contains circuits to handle both input (such as sensor readings) and output (such as when to fire the injectors). The firmware is like software, except that it is stored in the processor itself rather than on a disk.

Main Boards

Currently, there are two main boards available, V2.2 and V3. There is a third board scheduled for release in a few months known as Microsquirt.

V2.2 is a basic, low-cost board. It has all the basic sensor inputs and outputs needed to control fuel injection, plus spots where you can solder on additional inputs and outputs for features like spark control or electric cooling fans. If you are not interested in spark control, it will work just fine on its own. However, there are some inputs and outputs found on some cars that require either external devices or internal upgrades, particularly if you want spark control. For example, many distributors use a magnetic pickup called a VR sensor. If you want to control spark directly, you will need an external circuit to convert the output from a VR sensor into one the main board can handle. Another limitation is that this board is not designed to work with more than four of the low impedance injectors found in some newer cars and many aftermarket applications. Running too many of these injectors produces sharp voltage spikes that require either external resistors or adding a daughter card called a flyback board. (For more details on this, see the section on injectors and fuel systems in the MegaManual.)

V3 is the most advanced main board currently available for Megasquirt. Many of its improvements focus on reliability and ease of assembly. Heavy-duty components and extra cooling features mean that it can handle low impedance injectors without any upgrades. It also has several upgrades for ignition control. The main board can read VR sensors directly, and there is even a built-in ignition module so you can operate a coil directly from the Megasquirt. If you want to use Megasquirt to control a distributor-based ignition, this is often the best choice.

Microsquirt is a miniature, watertight version of Megasquirt. It resembles a V3 board in its features, only without provisions for large numbers of low impedance injectors. It also differs in having two independantly controlled ignition modules instead of one. The board is very small and sealed, making changes difficult. The Microsquirt comes fully assembled with a MS-II processor and uses an AMPSeal connector, while other versions use DB-37 connectors.

The bottom line: V3 is often the better choice if you want ignition control. In many cases, the extra built-in features can save more money than the extra purchase price will set you back. The V2.2 board can save you money in some cases when you do not need the advanced features of the V3 board, particularly if you want to run fuel only. Take a good look at the V3 page and think about what you plan to use; many common builds can use the upgrades. The Microsquirt is a specialized miniature version intended for such things as ATV's, motorcycles, and outboard motors where space is at a premium and you may not be able to protect the ECU from water.

Processors and Firmware

There are also two processors available, and each one can work with any full-sized Megasquirt main board. The standard unit is a Motorola 68HC908. You can upgrade this to the MS-II daughter card, which includes a faster HCS12-series processor, a built-in control for a stepper motor fast idle valve, and a network controller for future upgrades. The Microsquirt comes with an MS-II processor and cannot use the 68HC908.

If you are using an MS-II processor, there is currently one choice for firmware. The standard MS-II firmware controls both fuel and some of the simpler spark options. The spark control will work with most distributors, as well as the Ford EDIS and GM DIS coil pack systems. Installing one of these coil packs on an engine that never used one is relatively easy, the hardest part being adapting a crankshaft position sensor onto the crank pulley.

The standard processor has many choices for firmware. The original code controls fuel injectors and a fast idle valve, as well as switching the fuel pump on and off. The most popular upgrade is Megasquirt 'N' Spark – Extra (MSnS-E for short), which adds an enormous variety of extra inputs and outputs. As its name implies, it can control spark, using anything from a distributor to Ford EDIS to direct control of multiple coil packs. It also adds features like support for traction control, water injection, and many more. Currently, this version of the firmware has more features than the MS-II firmware, but MS-II is likely to grow to support features that are not possible with the standard processor.

Since Megasquirt is an open source project, all firmware is free. You can download both the firmware and its source code from several official and unofficial Megasquirt sites.

The bottom line: A standard Megasquirt processor can control fuel with its basic code, or fuel and spark with the MSnS-E firmware. The MSnS-E can also control many other user selectable outputs. It currently has the most options and features of any firmware for Megasquirt. The MS-II can control both fuel and spark, as well as a few user selectable outputs. However, the MS-II offers a faster processing speed and the possibility of future upgrades.

Tuning Equipment

In theory, if a computing device can run programs and connect to a serial port, you can program Megasquirt with it. There are several open source programs available to tune Megasquirt with a laptop, whether you're running Windows, MacOS, Linux, or UNIX. Laptops are not your only option, as there is also software available to tune your Megasquirt from many Palm handheld devices. Currently, Palm software does not work with MS-II, while there are laptop options for both processors.

Connecting the computer to the Megasquirt generally requires only a standard 9-pin serial cable. A good USB to RS-232 adapter can also work. Some of the more creative users have even rigged up wireless connections.

Other Devices

There are a couple of additional circuits you can buy to help install your Megasquirt. Some are test devices for helping assemble and tune the system, and can be removed once the car is running its best. Others become a permanent part of the installation.

The Stimulator is perhaps the most important. This board includes a battery connection, resistors to simulate sensor readings, and LED lights to indicate the condition of its outputs. It is probably the easiest way to test if your Megasquirt is functioning correctly. Every MS user should have one.

Fuel injection requires several fuses and relays to protect your components. The Relay Board puts all these in one convenient location and is suitable for mounting under the hood. It is very useful if you are installing EFI in a car that never had it to begin with. The price is often less expensive than trying to get the relays and fuse blocks from local auto parts stores. Highly recommended for installing in previously carbureted cars. If your car already has fuel injection to start with, you probably have all these parts already.

The MegaView is a display and tuning tool which can be built as either a plug-in device or a permanent dashboard display. It uses a digital display to show engine status and sensor readings. MegaView can also change some of the tuning paramenters. There are two different versions, one for the standard processor and one for MS-II.

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