In this circuit of an American documentation of the 90s, when the light is cut, we have the production of a pulsating tone. R3 determines the trigger sensitivity.
To use the instrument for AC measurement, the tips are A and B. For CC use tips A or B for...
The interesting circuit shown in the figure, can have its gain digitally controlled and present two...
This simple MW radio was found in a 1975 publication, but it can be mounted with BC548...