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 circuit presented was obtained in the 1994 Linear Applications Handbook from National...
This circuit indicates four levels of light, with an LDR sensor. The 47k trimpot adjusts the...
This circuit was found in a 80's Popular Electronics. The sensor can be any phototransistor. The circuit is...