Found in Popular Electronics from the 90's, this tuned to infrared modulated receiver uses a PLL. The circuit has a signal strength indicator.
In the figure below we have two triggers made with the LM3900 transconductance operational...
The trigger signal for this circuit is an audio tone. Tones up to close to 100 kHz can be used. The...
Found in an American documentation from the 90's, this 1.5 A power supply provides 1.5 to 22 V of...