This circuit is from 1980s documentation. The maximum operating frequency is 3.5 MHz. The current of the LED can be from 0 to 100 mA. The integrated circuits used are from that time.
The sensor for this Intersil circuit (1983 databook) is a common silicon transistor. The trimpot...
This circuit is from a 1980 publication. The circuit has high gain with weak signals and lower gain...
The integrated circuit used in this 1987 project is not very common these days. However, if found...