Here is the Megasquirt-II controller board all populated with components ( minus the processor ). All references to MS, or Megasquirt in these articles, generally refer to the Megasquirt-II PCB3. Look at the Bowling and Grippo site to learn about the different versions of Megasquirt.
Start with a kit
Although it is posssible to save yourself $100 or so buy purchasing a controller PCB only, and then ordering all of your components from Digi-key, I would strongly recommend that you save yourself some heartburn by getting a complete kit from one the many vendors listed on the Megasquirt site. I bought my stuff from DIYAutoTune and was happy that I did. Each component was in its own little polybag, with a label that described the part by ID as it would appear on the PCB ( R-21, etc.) as well as by component attributes, like 220 Ohm, color band pattern and so forth. Very helpful.
Assembly of the controller was straight-forward and can be done by anyone with basic soldering skills. A good way to warm up for the job is by assembling your stimulator kit first, since it is less critical, and you will need it anyway to test various circuits as you assemble the ECU.
There are only a few components in the MS-II that have very small and close-together leads that require some careful work and inspection to avoid solder bridging.
Plan your system first
There are some variations in the way that you will build certain circuits in the MS, depending upon the specific types of sensors and actuators that you will be using on your engine.
For instance, depending on how you will trigger the MS ( Hall-effect sensor, Variable Reluctor sensor, ignition coil, etc) you will build a slightly different circuit to accept the trigger signal. In my case, I am using a Ford EDIS ignition module to trigger the MS. The EDIS will get its signal from a crank-mounted trigger wheel, and Variable Reluctor sensor that I will install, so I instinctively started to build out the MS to take a Variable Reluctor signal. However, I actually needed to build the MS as if I were using a Hall-effect sensor, because the signal that the EDIS will pass on, is closer in wave-form to that of a Hall-effect than a VR sensor. Make sense? Exactly. You need to plan your system before you build the computer.
The only other stumbling block that I encountered was in the area of Idle Air control. If you plan to use a pulse-width modulated idle air control valve (as opposed to an on/off solenoid type) you will need to replace one of the transistors in the MS to handle enough current to drive the valve directly, since this type of valve cannot be operated by a relay.
Next came assembly of the relay board. The relay board is optional, and as the name implies, holds the EFI related relays as well as fuses. It also provides you with a single spot to wire in all of your sensors, injectors, and fuel pump – all of which can be hooked into the labeled terminal block.
If you are just installing a Megasquirt as a tuneable replacement for your car’s black box ECU, you will probably choose to use your existing relays, sensors, and wiring harness, and simply splice them into a pigtail cable that you will make to hook into the MS. Since I am installing an EFI system where none was before, I went with the relay board. The relay board is very simple to assemble. You won’t have any problems. I did, but that’s because I am an idiot. You will read the instructions and not install the relay sockets backward.
Now, before you can test your finished MS with some actual, real-world sensor data (since it did so well on the stimulator), you will need to get yourself a cable to hook the 2 boxes together. If I had this to do all over agian, I think that I would just buy a premade cable from one of the kit vendors, as this thing was a tad more labor-intensive to build than I had estimated. Instead, I bought a 24 inch wire bundle and built my own cable. The wire bundle came with all the wires that I would need, each a different color and in the appropriate gauge, and with their application printed right on them. In theory, you could just use a single color of 20 gauge wire for all of these, since they get wrapped up in tape and hidden anyway, but I wanted to be able to tap into the cable in case I wanted to add a MAF meter, or knock sensor at some future date. This way I will be able to tell which wire is which.
I cabled the MS to the relay box, hooked up a laptop via the Db-9 serial port, wired some sensors to the relay board’s terminal block, applied 12 volts to the system, launched MegaTune, and held my breath.
Sure enough, when I brought up the real-time display, I could see temperature data for the temp sensors, and when I turned the input shaft of the throttle position sensor, I got a nice smooth variation. What a geek! If it weren’t 2:00 AM I might just have dug up some vacuum line and tested out the Manifold Absolute Pressure sensor.