Found in a documentation from the 90's, this circuit already includes an amplification stage. The 12 V power supply allows its use in the car.
When the power is on, the 1 µF capacitor charges slowly by R1 and P1 until then on trigger...
The components used in this configuration are not common today. The circuit is from the 1982 SGS...
The integrated circuit used in this project is uncommon today, but the configuration can be...