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.
This circuit was obtained in an old American documentation. The integrated circuit used is...
RF or even switching transistors like the 2N2222 can be used in this circuit. The capacitors are ceramic...
This is a variation of the two previous circuits but controlling two LEDs. The brightness of the...