LOW RPM Tacho without magnetic pick up

dear all,
i get this design from internet **broken link removed**
1. Fin (frequency input on LM2907, Vout= Vcc x Fin x R1 x C1) is electrical frequency (in term i dont use magnetic pick up)?
2. what is the function of schmitt trigger ?
3. how to determine the value of each electronic component (R, C ) in schmitt and amplifier?

thx for helping

I suggest that you do a search for Schmitt Trigger in this forum and on the internet.

Briefly, it is a circuit that converts a varying signal on the input (eg. a sine wave) and outputs a square wave at the same frequency.

I don't wish to design the system for you.

ljcox said:

I suggest that you do a search for Schmitt Trigger in this forum and on the internet.

Briefly, it is a circuit that converts a varying signal on the input (eg. a sine wave) and outputs a square wave at the same frequency.

I don't wish to design the system for you.

Click to expand...

ok ..finally i found the way to determine the value of it

in schmitt's that resistor used for safety voltage regulator