In the video embedded below, he shows off a homemade voltage detector circuit that he constructed using a trio of BC547 NPN transistors. ... until reaching the indicator LED.

This simple LED current sensor measures a low voltage drop across a sensing (shunt) resistor. When the voltage exceeds about 10mV, the LED comes on. Two circuits are provided: One for sensing current ...

A voltage multiplier is applied as a high source impedance, 36V, 300mA, 12W LED driver. The high source impedance is ideal for driving power LEDs because it accommodates variations in LED junction ...

In the video embedded below, he shows off a homemade voltage detector circuit that he constructed using a trio of BC547 NPN transistors. The circuit is pretty simple though very useful all the same.

How to Use Cheap Electrical Testers and Voltage Detectors. Story by Chris Deziel • 9mo. Time: ... the LED will illuminate, ... The Circuit Tester. Also known simply as a voltage tester, ...

The current-control resistor for the alarm LED depends on the circuit’s operating voltage and the LED’s maximum current. Normally, 470 Ω is used. The low-cost, industrial-standard LMC555 IC ...

3. Flyback circuit ON phase: The MOSFET is switched on and a voltage is applied on the primary winding through the transistor. Energy is stored in the transformer’s core and the output Diode D1 ...