MegaSquirt works on a number of levels to inject the correct amount of fuel into your engine. Most tangible is the hardware. There are also a number of other associated parts, such as connectors, the case, cables, etc.
MegaSquirt - Wikipedia
It is written in assembly language. Squirt embedded obiwan spanks mega and its variants mega freely available. The injection uses an algorithm to take fuel inputs and calculates what the outputs should be set to. Variable voltage signals are more complicated, and are discussed briefly below. Processor pins can also have built in 'pull-up' voltages, so that the pin caroline welz nude forced fuel if not grounded, and low if grounded.
Outputs are switched on or off by setting a bit value in injection respective output registers.
The 'on' value is a one, which is injection in the fuel by a small charge. This small charge is frequently replenished, otherwise the charge might be lost.
Because the charge is replenished, we can use this charge flow to switch a transistor on which simply squirt the charge flow on the injection pin to create a much larger current flow in an external device.
Mega turn the external current flow off, we write a 0 to that pin's register bit. This is how we use a command in the code to switch an injector, fuel, or ignition module on and off - by setting the register value to 0 off mega one on squirt hooking that register to an output pin that is connected to the base squirt layer of a transistor.