I need help in how to make a tach with a multimeter

[Gilbert]

Hi, I got a multimeter with a frequency setting, and also have a car
timing light with a detachable coil pickup.
I want to be able to read rpms from small 2 stroke engines and I was
thinking in using the coil pickup with a zenner diode.
The multimeter needs from 200 mv rms up to 10v rms to read properly
I remember that the timing lamps work this way: the signal from the
pickup is transformed to a pulse that is feed to a scr that pulses the
light. Could I connect the MM at the input of the SCR?

 

[petrus bitbyter]

Hi, I got a multimeter with a frequency setting, and also have a car
timing light with a detachable coil pickup.
I want to be able to read rpms from small 2 stroke engines and I was
thinking in using the coil pickup with a zenner diode.
The multimeter needs from 200 mv rms up to 10v rms to read properly
I remember that the timing lamps work this way: the signal from the
pickup is transformed to a pulse that is feed to a scr that pulses the
light. Could I connect the MM at the input of the SCR?

As long as you leave the lamp in place, you can get the pulses from the
lamp-SCR connection. Nevertheless you'd better take some precautions to make
sure to keep the pulses always below the 10V you mention. The pulses may
contain some nasty spikes that do not harm the lamp but your multimeter will
not like them.

petrus bitbyter