This 555-based circuit was found in the August 1976 issue of Radio Electronics magazine. The tone frequencies are provided by the capacitors connected to the 555 IC.
With this circuit it is possible to control the frequency of a 555 astable, given by C1 and R1...
This small pulse receiver had its construction described in a Radio Electronics magazine from...
We found the circuit of this Japanese transistorized commercial receiver in a documentation from...