This circuit was found in a March 1988 Radio Electronics. The voltage scale is set at R3. 19 LEDs are used in this indicator circuit.
This circuit indicates when a 28 V lamp burns, lighting a neon lamp with higher voltage. The...
This circuit, which can be used on an optical link, is suggested by the Texas Instruments...
We found this circuit in a 1992 Popular Electronics. The circuit has an optical sensor with LED...