The speed giver in my car gives "mass" impulses proportional to the speed. About 7 impulses in one wheel revolution, 7 times is mass, and 7 times is nothing:





Because of different tires radius (don't ask why...) the speed giver is not correct any more...

So I need to correct it by multiplying it with a Real number (about 1.123).

How can it be done without using a microcontroller?

Can impulse be turned to linear voltage, and then changed with variable resistor, and turned back to impulses?

 

You can use a pair of LM2907's and an op amp. Use one 2907 to do a frequency to voltage conversion. The op amp applies the corrective gain with the right resistor network, and the other 2907 does a voltage to frequency conversion.

 

Can you provide me the scheme?

 

That is a general solution. The nature of the speedometer pulses and the input they feed would be necessary for a circuit. The input 2907 might need buffering and the output 2907 might have to have its frequency altered in some way. I can't tell without those details.

You might get the data sheet for an LM2907 and see what you think.