The circuit was made back in 1980's (not by me :) ). I draw this by reverse engineering the circuit.
I just modified few components:
- first added a diode in series with zenner 8V2 and change the 9V1 zenner with a 10V one.
- second I changed the value of 330 ohm resistor in 100 ohm (in fact I change the resistor with a 300 ohm trimmer)
- third I change the value of 330 ohm resistor in 760 ohm (in fact I change the resistor with a 2kohm trimmer)
- another resistor to play with is 56 ohm in colector-base of transistor
This circuit is a request from my neighbor for his old wolkwagen passat to checking the charging voltage
