AC mains voltage indicator

Here is simple and very useful circuit AC mains voltage indicator, indicates the voltage level of AC mains by three different LEDs. AC mains voltage indicator circuit can be made and assemble even by beginners.

Circuit description of AC mains voltage indicator

All three LEDs of AC mains voltage indicator are connected between collectors of transistors T1, T2, T3 respectively. Here potentiometer VR1, VR2, and VR3 are used to adjust the base voltage of transistor T1, T2 and T3 respectively. As shown in circuit diagram first AC mains is stepped down by 9V-0-9V transformer and then rectified by a signal diode D1 and smoothed by C1 which give output 25V DC. This circuit is work on the principle, when AC mains vary DC voltage also varies proportionally and sensed by transistor T1 through T3.

For setting the low level voltage, a manual AC voltage regulator (MVR) should be connected to the primary of transformer X1.  Now set AC voltage of MVR to about 175V and slowly potentiometer VR1 adjusted until voltage across the base of transistor T1 reaches 9.7V and transistor starts conducting which glow LED1 and stop glowing when the base voltage drops below the preset value. This process is repeated for 200V and 230V in which LED2 and LED3 glows respectively.

Now connect this circuit to AC mains, if the voltage drop below 175 volts no LEDs glow. First, a high voltage (more than 230V) is indicated by all three LEDs glows (LED1, LED2, LED3). Second, normally voltage (200V-230V) is indicated by two LEDs (LED1 and LED2). Third, a low voltage (175V-200V) is indicated by the glowing of LED1 only.


Resistors (all ¼-watt, ± 5% Carbon)

R1- R6= 1 KΩ

VR1 – VR3 = 10 KΩ


C1 = 220 µF/50V


T1 – T3 = BC547

ZD1 – ZD3 = 9.1V zener diode

D1 = 1N4001

LED1 – LED3 = Simple LED


X1 = 230V AC primary to 9V-0-9V, 250mA secondary transformer

SW1 = On/off switch

4 thoughts on “AC mains voltage indicator”

    1. You just need to a 150V to 9-0-9 Volt transfer to change the voltage from 150-250 voltage.

      And if your transformer with that voltage change another option will be to set Vr1 , Vr2 , Vr3 according to the output you require.

  1. sir please send me a detailed information about my project VISUAL AC MAINS VOLTAGE INDICATOR
    Sir its urgent

    1. Sorry , We don’t have the feature of sending project reports or details on emails. However you can subscribe for project updates from the subscription widget in right side of the website.
      The only details we offer is what is written in the project description page here.

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