This circuit for currents from 500 mA to 1.5 A was found on a Ham Radio from the 90s. R4 determines the current in the load under test. Transistors must be equipped with radiators.
We found this circuit in an 80's Radio Electronics. The circuit uses a PTC sensor and an LED...
In this circuit a 12 V lamp or LED blinks with the music signal applied to the input. R depends on...
Using a period sensor, this circuit was found in the February 1986 issue of Radio Electronics...