This circuit uses an optical coupler to indicate a phone call through a lamp. The circuit is from a Hands-On Electronics from the 90s. The lamp must be incandescent.
The figure below shows an AC transconductance amplifier with the National Semiconductor LM3900. The...
This common circuit using operational amplifiers was found in the 1993 issue of Radio Electronics Special...
This circuit provides a voltage at the output only when the input voltage exceeds a value that...