Simple Mains Voltage monitor LM324

It does not use a isolation step down transformer. This has to be constructed only by skilled people with knowledge of safety requirements.

Battery Monitor for your Boat or Car

C1 0.47uF can be brought down to 0.22uF for low LED currents, use high efficiency ultra bright LEDs.C1 should be 440V AC or 630V DC plastic axial yellow, polyester, polycarbonate, polypropylene, metalized film.

R3-R6-R9-R14-R18 resistor divider determines the LED turn on or threshold switch points, 10M for hysteresis.

Resistance Measurement Analog LED Meter

Adjust R16 preset with a log Plastic tweaker to get the led D2 to turn on when input voltage is at 220V AC. This has to be done after PCB is put in a sealed fire-retardant-plastic or epoxy box. drill a hole in box for plastic tweaker.

This Circuit is Not a Tested Design. It is an Idea for study

Warning :

This Circuit is Mains Operated without Isolation Transformer and will give lethal electric shock if touched when the circuit is turned on. Test circuit only with DC 9V Bench Power Supply to try it out. Do not use 230V AC.

Battery Level Indicator - Similar Circuit that is used to measure Low DC Voltage like a battery.

When you use a capacitor powered supply you get a small current but no heating. Resistor based power has even lower current and there is heating. These are very low power encapsulated devices only.

Transformer based supplies are safe and generate very less heat and can deliver much more current. The Size of transformer increases with current. Finally we have SMPS the most popular with moderate heating and small size even for large currents. Then SMPS have to be designed for high reliability. There were Thyristor based power supplies but they are largely replaced with Mosfet and IGBT based ones.