The indicated circuit uses an unusual buffer from National Semiconductor. The frequency is given by resistors R1 and R2 as well as capacitors C1 and C2.
With this circuit, from an old operational datasheet, it is possible to measure the CMRR,...
Found in a Popular Electronics from the 90s, this circuit can be adapted to use LEDs. The power...
The circuits shown in the figure, that of an infrared video signal transmitter and receiver, were...