Two LEDs with different light color (e.g., red and green) you can gather simple indicator for voltages from 4.5 to 220 V. It is also capable to determine the polarity of the source in the interval 8-220 V. When measuring AC voltage both glow diode, and if it is permanent - one of them glows in depending on the polarity of connection of the indicator. The proposed scheme Czechoslovak journal "Amaterske Radio".
To measure mains voltage from 110 to 220 In need short-term to overheated current limiting resistor R1 (see Fig.). In addition to home appliances, the indicator is used and motorists.
Czech Zener 1NZ70 can be replaced with domestic stress stabilization 5-6 In, for example GA, diodes V1 and V5 - any low-power silicon, for example D226. LEDs can be ALB (red) and AL 102V (green).