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.
We found this configuration in the Linear Applications Handbook of the National Semiconductor of...
This transmitter for the FM band was found in a 1993 spy documentation. The coil consists of 2 + 4...
This circuit was found in a 1980s American documentation. Operational amplifiers are from that...