Circuit detectors and sensors based electronics projects

Using this circuit diagram can be made a simple connection circuit with touch sensor. This circuit allows delayed disconnection of the connected device, meaning that the circuit will remove power after a set time period.
Using this electronic circuit is possible to switch a device with a maximum consumption of 300 mA.
The main components are the six trig Schmitt contained in an integrated circuit type 4016.

Using this scheme can be made a network voltage indicator electronic circuit. If the input voltage is present across the network, the optocoupler transistor is open, T1 is blocked and controlled rectifier, Th1, is in a state of conduction. Since both terminals of the piezoelectric buzzer is at the same potential, buzzer is off. If voltage disappears, the transistor T1 enters the conduction and thus makes the terminal of buzzer to be put on the ground (maintains thyristor conduction state).

Using this electronic scheme can be made a very simple function indicator that generates a tone of each two minutes. This function indicator can be used to warn that a certain electronic equipment is still under voltage, or to generate an audio warning, consisting of 5 to 10 beeps.