This circuit is from American documentation from the 1980s. The transistors are general purpose types and the relay can be 6 or 12 V depending on the supply voltage.
This receiver activates a relay from signals emitted by a 27 MHz modulated transmitter as...
This somewhat critical circuit was found in a year 2000 documentation. The frequency depends on...
This circuit can be used as a residential doorbell. We found it in an English publication from...