This circuit was found in documentation from Analog Devices from the 90s. The circuit uses components from that time, which are uncommon today.
This simple detector was found in Popular Electronics from the 1990s. Both the phototransistor and the PNP...
This circuit for low frequencies was found in a Radio Electronics from February 1965. The...
This CMOS frequency meter can measure frequencies up to about 1 MHz with a 3-digit resolution. The circuit is...