Schematic Diagram

This is a schema that detects tesões 1.8 V up to 230 Volts AC or DC. This schema is not a novelty, but it proved so useful, simple and cheap that every technician should have one on the bench.

When the tip (red) positive is connected to a positive DC voltage and the black lead to the negative, the red LED lights up. Reversing the polarity green LED lights.

Connecting the probes to an AC source both LEDs will light. The lamp current is limited to 40mA @ 220V AC LED for illuminating and a filament starts from about 30V, shining more intensely with increasing tension.
Therefore, due to the behavior of the lamp filament, any voltage in the range from 1.8 to 230 V can be detected without changing component values​​.

 

List of Components

D1________5 or 3mm. red LED
D2________5 or 3mm. Green or yellow LED
LP1_______220V 6W lamp filament
P1________ Tip multimeter red
P2________ Probe Multimeter Black