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Hmm, I think we have a lot to discuss concerning tachometers.
First of all, tachometers, as you are probably already aware, requre some kind of frequency-to-voltage conversion to work from a spinning shaft/ignition pulse train/etc.
Your experiment that 1.5 volts DC sends the tach meter movement to about mid scale is a good start, but simply connecting the meter movement to any source of signal derived from a rotational generator is not going to give you what you are after. Even if the match-up was corrected via a variable resistor, you would still be looking at a reading that was non-linear with the speed of the shaft.
A petrol engine tachometer takes a pulses train from the ignition system of the distributor and converts the frequency of the pulses (which is directly proportional to the engine speed) and converts it to a DC voltage/current to run the meter.
The optical sensor tachs do the same thing, except that the pulses are generated by an optical interrupter.
On some diesel engines, a sample of the three phase AC power from inside the alternator is supplied to the V/T converter .There are "black boxes" that can do the conversion and will program for rough calibration of a petrol tach from a variety of frequency generators. See this page for a $60 converter that does this. The generation of the pulse train is up to you.
I can show you how to build a complete tachometer using junk box parts costing $10. All you need to do is couple a disc, gear, or similar serrated interrupter to your motor shaft. A small AC generator of some sort would also work. It's possible that the circuit could be cobbled together to sense motor commutation spikes, but I've never fiddled with that.
First of all, tachometers, as you are probably already aware, requre some kind of frequency-to-voltage conversion to work from a spinning shaft/ignition pulse train/etc.
Your experiment that 1.5 volts DC sends the tach meter movement to about mid scale is a good start, but simply connecting the meter movement to any source of signal derived from a rotational generator is not going to give you what you are after. Even if the match-up was corrected via a variable resistor, you would still be looking at a reading that was non-linear with the speed of the shaft.
A petrol engine tachometer takes a pulses train from the ignition system of the distributor and converts the frequency of the pulses (which is directly proportional to the engine speed) and converts it to a DC voltage/current to run the meter.
The optical sensor tachs do the same thing, except that the pulses are generated by an optical interrupter.
On some diesel engines, a sample of the three phase AC power from inside the alternator is supplied to the V/T converter .There are "black boxes" that can do the conversion and will program for rough calibration of a petrol tach from a variety of frequency generators. See this page for a $60 converter that does this. The generation of the pulse train is up to you.
I can show you how to build a complete tachometer using junk box parts costing $10. All you need to do is couple a disc, gear, or similar serrated interrupter to your motor shaft. A small AC generator of some sort would also work. It's possible that the circuit could be cobbled together to sense motor commutation spikes, but I've never fiddled with that.
