So there are inventive types out there and there has been discussion on having a tach for the T motor.
So where is the tach that uses the magneto to measure engine RPMs?
The Buzz tach made by Buzz Pound did just that.
A bit more information please... Did the Buzz Tach read pulses from the magneto magnets?
The model T magneto is a variable amplitude speed dependent variable frequency source.
A tachometer is a frequency to voltage converter.
"Did the Buzz Tach read pulses from the magneto magnets?"
It read the frequency of the voltage from the mag and as Bob said, converted it to an analog reading on a sweep hand gauge.
Bob may have said that, but he said it in technical terms that the average guy couldn't translate! So, it seems the answer is "Yes, the magneto can run a tachometer."
Here is another example: This Tachometer uses the magneto to measure engine RPM..... and magneto RMS output voltage, and magneto internal resistance and magneto magnetic field strength.
Engine RPM is calculated by measuring the time between magneto voltage pulse frequency and calculates engine RPM knowing there are 8 (positive) magneto pulses per crank shaft revolution.
Sorry for getting out of control with "Jargon".
I actually did a little fooling around with the Mag-Tach concept.
My preliminary findings showed that the AC Sine-wave from the mag became very noisy when the coils were operating.
This project is "On-The-Stack" now that I am retired.
In general, I thing a reasonably accurate Tach that runs from the Mag is doable.
That's OK, you probably didn't even give it a second thought when you posted! When we work with a specialized technology a lot and a long time, often time we don't realize when we are talking "gobbledygook" to others!
When you get back to the project, it sound like it might be a neat addition to the T world.