Ultra-simple Voltage Probe
RED Free Circuit
Detects 1.8 to 220 Volts DC or AC
Minimum parts counting
D1________5 or 3mm. Red LED
D2________5 or 3mm. Green or Yellow LED
LP1_______220V 6W Filament Lamp
This circuit is not a novelty, but it proved so useful, simple and cheap that
it's worth building.
When the positive (Red) probe is connected to a DC
positive voltage and the Black probe to the negative, the Red LED
Reversing polarities the Green LED illuminates.
the probes to an AC source both LEDs go on.
The lamp limits the LEDs current
to 40mA @ 220V AC and its filament starts illuminating from approx. 30V, shining
more brightly as voltage increases.
Therefore, due to the lamp's filament
behaviour, any voltage in the 1.8 to 220 Volts range can be detected without
changing component values.
Note: A two colors LED (Red and Green) can be
used in place of D1 & D2.