This is a typical point scale or moving bar circuit with the LM3915. We found it in old American documentation. The operational amplifier supports an equivalent modern type.
This triac circuit was taken from an article in the July 1970 Radio Electronics magazine. Note the...
Signals ranging from a few millivolts to a few volts can be used to excite a relay with this...
This circuit was found in American documentation from the 90's. The transformer determines the...