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.
In the figure we have a sensor circuit that makes use of common transistors and a photo diode as...
November 2016 - Already available from Mouser Electronics on Texas Instruments' new DS280BR820...
Schmitt Triggers convert a signal of any waveshape in square signals or pulses. The circuit shown...