The difference between this circuit and the previous one is that it uses PNP transistors. The circuit is from Radio Electronics magazine from July 1968. The frequency depends on R1 and C1.
This circuit allows you to read resistors up to 20 M ohms, converting it into voltage. The circuit is...
The circuit in the figure is a useful continuity test serving to check the condition of circuits and...
This circuit beeps when the sensor is triggered by the opening of the freezer door or other...