Help me build an inductive tachometer circuit

[mauricio]

I want to build a circuit that will pick-up induction from a pulse generated by an engine sparkplug and create a nice digital signal from it..

Any help will be apreciated !

 

[brumi]

inductive tachometers

Estimado, necesitas una bobina captora , un amplificador y conformador de pulsos y por ultimo un contador.
Hay cuenta vueltas que se utilizan el karting y motociclismo que funcionan de esa forma.
La bobina captora es del tipo de una pinza amperimetrica para poder cambiarlo facilmente de vehiculo.
El amplificador con un simple amplificador operacional y el conformador de pulsos con un smith trigger.

 

[Freddybaby]

what is inductive tachometer

I made a similar tach for small gas engines, I used an LM395 transistor as the input conditioner for an LM555. The LM395 is an industrial type transistor with gate protection up to 40V. Put about 5-10K in series with the gate and some zener protection to clamp over say 30V. Use bypass caps across the emitter/collector (.1uF)

A single wire wrapped about 10 turns will couple the pulse. I didn't need any filtering on the input but definitely use some voltage clamping. Maybe across the coll/emitt too.

 

[ansh1208]

karting tachometer circuit

Freddybaby I request you to please draw the circuit diagram. I'm also trying to make a tachometer for car but due to huge vehicle electrical noise i'm not able to get through.

 

[Freddybaby]

tachometer

It was a long time ago, don't exactly remember the fine details but here is a schem that is similar. The difference was I used an LM395 for the trigger input, the base tied to the tap coil around the spark wire.

Again, this was for a lawn mower so perhaps there was less noise. Definitly less energy in the spark.

You say yours is not working, please post your schem and maybe we can figure it out. The timing adjustments can be tricky for pulse type sensing but as long as your input is low when the timer wants to reset you should be ok..