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.
In this 1974 circuit, the Triac fires when the neon lamp reaches its ionization voltage of around 85...
The circuit shown in the figure is suggested by National Semiconductor and is based on an...
The 7401 is a different member of the TTL family, as it consists of four NAND ports, but with the...