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While the MegaSquirt official documentation covers almost any question someone may have about the system, it can take a lot of reading to find the answers. We've had a few BangShifters asking for a thread on the basics of the system here, so I thought I'd start one. For those of you who haven't heard of the MegaSquirt at all, it's basically a kit to build your own EFI controller, much like old Heathkits. Although now you can often buy them ready made, too, and a few versions only come fully assembled. I'll start off with an introduction to the devices in the MegaSquirt family, and a couple of common questions.
Standard MegaSquirts
These have both a processor number and a main board number. The processor can be switched out, allowing you to start with one version and upgrade later, but upgrading boards is another story.
Main board types in production now:
V2.2: Very similar to the original, basic MegaSquirt design. Has two outputs for driving high impedance injectors, a fuel pump output, an on/off idle speed control output, and basic sensor inputs, including an onboard MAP sensor.
V3.0: This board adds a VR sensor input (aka a magnetic pickup), the ability to run large numbers of low impedance injectors, more provisions for ignition control, and more noise resistance. Currently the best-selling main board, and likely to be that way for a while.
V3.57: Basically, you're looking at a machine assembled V3.0. Adds a couple minor improvements such as making PWM (Ford style) idle control standard and the ability to select the ignition input with pull-off jumpers instead of hardwired ones. Not sold as a kit.
Note that it's often possible to add a lot more features than the ones I listed, through expansion boards, jumper wires, and sometimes even hot gluing extra transistors to the main board.
And the processor types.
MegaSquirt-I: Originally meant to control just fuel, it didn't take long for people to figure out how to modify the code to support basic, and sometimes not so basic, ignition control.
MegaSquirt-II: A faster processor with about 100 times the injector control resolution of MegaSquirt-I. It also adds a stepper IAC driver chip, CAN communications that let it talk to other MegaSquirt-related devices, and a lot of new code features.
Other MegaSquirt hardware
Stimulator: A board that simulates the signal from a distributor and many of the sensors on an engine. Has blinking lights that respond to MegaSquirt outputs. Lets you test a MegaSquirt without putting it on the motor, for troubleshooting purposes.
JimStim: A more sophisticated version of the Stimulator that can simulate a variety of crank angle sensors, and test more outputs. Naturally, it adds more blinking lights, too.
Relay board: A MegaSquirt-specific relay module that can be used for rewiring a car from scratch.
MicroSquirt: A miniature MegaSquirt-II based device, although it is missing a couple of the full sized version's features. Intended for things like motorcycles, but does turn up on cars.
MicroSquirt Module: A small circuit board with many of the key functions of an ECU. Generally meant for third party companies to drop into their own devices, making for a cheap way to build a standalone ECU.
eMS-Pro: A MegaSquirt-I based device that is related to the V3.57 board. Intended to give the MegaSquirt more functions without needing modifications, it adds a lot of inputs and outputs, such as nitrous control and boost control.
GPIO board: Stands for General Purpose Input and Output. A bit more science project like than other MegaSquirt boards, it's designed so that you can put it together in different way to get different functions. The most common use is automatic transmission control, but it could also be an EGT measuring device or work like an OEM body control module. Can communicate with MegaSquirt-II based devices.
MSPNP: A MegaSquirt built to plug into an OEM harness. Currently available for Miatas.
DIYPNP: A build your own kit with an OEM ECU connector, based on the MicroSquirt Module. Can be configured to match different OEM pinouts. Currently only available for imports, but that will change.
Future MegaSquirt items
MegaSquirt-III: A processor upgrade you can add to existing MegaSquirts. Not only does this one add more processor speed, it adds internal data logging with an SD car and the ability to add an expansion card for sequential fuel and ignition, as well as a lot more inputs and outputs.
MegaSquirt-II Sequencer: A Microsquirt-like device, only about twice as large (making it about 2/3 the size of a regular MegaSquirt). Uses the MegaSquirt-II processor and a second processor for sequential fuel injection.
Standard MegaSquirts
These have both a processor number and a main board number. The processor can be switched out, allowing you to start with one version and upgrade later, but upgrading boards is another story.
Main board types in production now:
V2.2: Very similar to the original, basic MegaSquirt design. Has two outputs for driving high impedance injectors, a fuel pump output, an on/off idle speed control output, and basic sensor inputs, including an onboard MAP sensor.
V3.0: This board adds a VR sensor input (aka a magnetic pickup), the ability to run large numbers of low impedance injectors, more provisions for ignition control, and more noise resistance. Currently the best-selling main board, and likely to be that way for a while.
V3.57: Basically, you're looking at a machine assembled V3.0. Adds a couple minor improvements such as making PWM (Ford style) idle control standard and the ability to select the ignition input with pull-off jumpers instead of hardwired ones. Not sold as a kit.
Note that it's often possible to add a lot more features than the ones I listed, through expansion boards, jumper wires, and sometimes even hot gluing extra transistors to the main board.
And the processor types.
MegaSquirt-I: Originally meant to control just fuel, it didn't take long for people to figure out how to modify the code to support basic, and sometimes not so basic, ignition control.
MegaSquirt-II: A faster processor with about 100 times the injector control resolution of MegaSquirt-I. It also adds a stepper IAC driver chip, CAN communications that let it talk to other MegaSquirt-related devices, and a lot of new code features.
Other MegaSquirt hardware
Stimulator: A board that simulates the signal from a distributor and many of the sensors on an engine. Has blinking lights that respond to MegaSquirt outputs. Lets you test a MegaSquirt without putting it on the motor, for troubleshooting purposes.
JimStim: A more sophisticated version of the Stimulator that can simulate a variety of crank angle sensors, and test more outputs. Naturally, it adds more blinking lights, too.
Relay board: A MegaSquirt-specific relay module that can be used for rewiring a car from scratch.
MicroSquirt: A miniature MegaSquirt-II based device, although it is missing a couple of the full sized version's features. Intended for things like motorcycles, but does turn up on cars.
MicroSquirt Module: A small circuit board with many of the key functions of an ECU. Generally meant for third party companies to drop into their own devices, making for a cheap way to build a standalone ECU.
eMS-Pro: A MegaSquirt-I based device that is related to the V3.57 board. Intended to give the MegaSquirt more functions without needing modifications, it adds a lot of inputs and outputs, such as nitrous control and boost control.
GPIO board: Stands for General Purpose Input and Output. A bit more science project like than other MegaSquirt boards, it's designed so that you can put it together in different way to get different functions. The most common use is automatic transmission control, but it could also be an EGT measuring device or work like an OEM body control module. Can communicate with MegaSquirt-II based devices.
MSPNP: A MegaSquirt built to plug into an OEM harness. Currently available for Miatas.
DIYPNP: A build your own kit with an OEM ECU connector, based on the MicroSquirt Module. Can be configured to match different OEM pinouts. Currently only available for imports, but that will change.
Future MegaSquirt items
MegaSquirt-III: A processor upgrade you can add to existing MegaSquirts. Not only does this one add more processor speed, it adds internal data logging with an SD car and the ability to add an expansion card for sequential fuel and ignition, as well as a lot more inputs and outputs.
MegaSquirt-II Sequencer: A Microsquirt-like device, only about twice as large (making it about 2/3 the size of a regular MegaSquirt). Uses the MegaSquirt-II processor and a second processor for sequential fuel injection.
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