I'm attempting to convert my 67 Sunbeam Alpine Smith's Jaeger inductive tachometer to work with a square wave tach output on a DSM style mazda ignition module. I don't want to fry this thing so I'd like a second set of eyes if possible.

Its 2 germanium transistors that from the factory and the power wire to the coil is looped around a transformer that causes the voltage to drop and trigger the 1 shot to power the magnets in the tach coil. Since the new engine has coil packs that is not going to work, so the square wave output from the ignitor will have to be used.

I think replacing the transformer with a PNP transistor will let the rest of the factory components do their thing with the square wave triggering it.

Thoughts? Did I leave any parts out? If you think it will work any suggestions for resistance values? I believe its 12v, unknown duty cycle but I don't think that matters with a monostable circuit.

Here is the tach, along with a schematic I found on a tach rebuilding website next to what I think should work.

Good luck! You lost me in the 1st sentence.

I recognize that the post was written in English, but beyond that... best of luck!

replace the flux capacitor and drive 88?

I speak chemicals. My father speaks electrons. We made a pact not to speak about either item, as we both get glassed-over eyes.

But I can ask/forward him.

~egon

oh man, my intro to electrical reinforced my decision to stay in mechanical.

Bro, do you even circuit?

Going from germanium to PNP seems like a good idea, but I'm a little lost on how the square wave is going to get translated into a usable signal for the tach?

You need a dikfer to make it work. Problem solved.

KY AG I'll explain it as I understand how it works. I'm obviously not an EE, so I'll be using hillbilly language

The 2 germanium transistors are switches. As the points close and charge the coil current flows through the wire across the transformer. Transformer is wired "backwards" compared to the 12v to the 1st transistor so it causes enough of a voltage drop to fire the transistor (PNP, so it is on when the voltage is low, off when high) When transistor 1 is on it charges the resistor capacitor circuit that powers transistor 2. The RC network is tuned to drain from 12 to 0 for XXX microseconds. While it is not drained transistor 2 is turned on for XXX microseconds and powers an electromagnet that bumps the tach needle. So lots of pulses across the coil power wire cause the tach to work.

Im thinking if I rip out the part that converts the current pulses to logic pulses and just use the logic pulse from the mazda ignition module tach output it might work.


Someones got to know. If there was a question about material strength or suspension design everyone on here who has ever sat in ENGR111 will claim expertise. Where are all the EEs?

The only right answer is the one that turns it into a tiger.

Maybe cross post on Nerdery?

Dubi if I was wondering which gamestops allow you to smoke pot while playing call of duty on the demo ps4 the nerdery would be a perfect forum, but this is serious business.

quote:

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Dubi if I was wondering which gamestops allow you to smoke pot while playing call of duty on the demo ps4 the nerdery would be a perfect forum, but this is serious business.

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Point made. I need that job!

I would drive the input from an optoisolator. It would remove a lot of hassle dealing with keeping the bias correct since this all direct coupled. Will try to look at schematic on something other than my phone with more specific comments