This circuit is from the Linear Applications Handbook of the National Semiconductor of 1994. Transistors are common, but the integrated circuit is not easy to obtain today.
Any general-purpose germanium or silicon PNP transistor can be used on this receiver. The handset...
When this circuit is activated the LED flashes for a moment indicating that the function has been...
In the circuit of the figure, when pressing S1 the sound varies according to the value of R2 and...