This interesting sensor for RF signals was found in an article in the June 1989 Radio Electronics magazine. It is a field strength meter with an LED bargraph indicator.
This decoder TTL circuit for 15-channel remote control was found in Selezione Radio, Italian...
This is the circuit of a sensitive voltmeter using a difficult-to-obtain 5 uA full-scale...
This circuit compares two light intensities, providing the indication on an analog instrument. The...