Found in American documentation, this circuit for modulated infrared signals can be tuned to a certain frequency. The photodiode can be of any type.
Hartley oscillator operates in the audio range. Frequency can be adjusted by P1 and also depends...
This circuit is intended to manipulate a transmitter (CW) from coded audio signals recorded on a...
This circuit was found in a 90s Popular Electronics. The integrated circuit used is similar to the 741....