We found this circuit in an old Mullard (Philips) documentation on the 555 and 556 integrated circuit (double 555). The relay must be 12 V with contacts that support the horn current.
If you touch the sensor for a moment, the LEDs run and when you stop touching the sensor, only one...
This notch filter uses four operational amplifiers that can be 741 instead of the original ones....
In this circuit the LED lights up when the input voltage exceeds the value set in the trimpot. The circuit...