I have a question about measuring the average voltage being delivered to a circuit. Basically what I want to do is tap into the line coming from the ECU to the fuel injectors in my car. The ECU sends a pulse signal to the injector to signal the injector to open and start spraying fuel into the intake. I figure that if i can measure the average voltage on this line then i can know what percent of the time the injector is open. then knowing the fuel delievery rate of my injector and my speed i should be able to calculate an instantaneous gas milage value. Eventually i'm going to do this digitally with A/D's and a LCD output so that i can monitor a number of variables. But right now i want to do it all analog. That it's I'd just like to have a (analog) voltmeter that reads a voltage that is proportional to the average voltage being sent to the injector. I figure that for high frequencies that any typical analog voltmeter is going to read the average voltage, but what happens at idle when the frequency is going to be something like 4-8Hz? does a typical analog voltmeter average over that range too or does it start to look DC at 8Hz?
(for the car experts out there: i can't use OBD-II and get this info, as my car is an '89 and predates OBD-II by many years).
if anyone has any ideas that would make my life easier, i'd appreciate it!
mike