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Mains Voltage monitor using LM3914

This Circuit helps in the monitoring of mains supply voltage. LM3914 bar graph indicator is used for a better display. It is just like an LED Analog Voltmeter.

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

Microohm Meter with LED Analog Bar

C1 limits the current and drops most of the voltage. The zener regulated supply is for the chip. C2 can be raised to 220uF or more if required. The bar mode display may consume more power. Use dot mode only on capacitor power. Bar mode will need a bigger cap or a transformer supply.

LM3914 - Versatile and Easy use Display

R2-R3-R5-R6 form a voltage divider to get a sample of the input voltage, D11-C3 get the DC value.

Adjust R5 preset with a log Plastic tweaker to get the 5th led to just turn on when input voltage is at 138V 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.

Mains Voltage monitor using

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.

LM3914 meter for 25 V DC

Have a look at the TI application note which has many examples. Understanding this will help you make your own solution.

LM3914 - Dot/Bar Display Driver

 20-Segment Meter with Mode Switch

20-Segment Meter with Mode Switch - Cascading is required if you want more resolution. Example for measuring 20V, you want to show in 1V per LED steps. It can withstand +/- 35 Volts input upper limit. The inbuilt reference is 1.2V use it as shown in the Typical Application. This also helps in setting the brightness of LED display. You may need to use external attenuators, buffers or precision  rectifiers to measure AC voltages or High Level DC voltages.

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20th May 2020


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