This circuit indicates a digital value through a moving bar. The circuit is TTL and must be powered by 5 V. We find this circuit in a Texas Instruments optoelectronics manual.
The circuit shown is suggested by National Semiconductor's Linear Applications Handbook. The base...
This circuit uses a pickup coil to take the signal from a telephone line without contacts. The circuit...
In this circuit, the transistors are NPN for general use and the phototransistors can be replaced by...