Amplifying pulses.

My present device does much the same - one transistor a few components and one transformer. ;-)

I've not actually measured it. Worked the other way round and found that the tacho will trigger reliably with a 15v peak pulse.

Thought I'd given it earlier.

The output from the ECU is pulses peaking at 5 volts on my scope. The tacho needs pulses peaking to 15v to trigger reliably.

still not giving the necessary info, good luck

I'm not quite sure how you get a 15 volt plus output from an 'audio amp' running off a 12 volt rail?

The tacho input impedance is approx 6M.

bridge mode, but we cant do that as one size of the tacho needs to be earthed..

So as I said, we need to either produce a higher rail voltage with maybe a capacitative charge pump, or use an inductor.

Charge pump would be good enough at that sort of impedance.

Here's the simplest form.

Now we know its 6M it becomes a lot more doable. The usual way to get above rail votlage is to use a switched mode power supply, tiny power ones are very simple to make. 2 transistors and an M3 bolt IIRC. At those powerlevels you can simply use resistance to protect against overcurrent.

Or you can use the pulses output themselves to create an above rail second rail, driving a 2nd output from the first.

NT