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
It does not use a isolation step down
transformer. This has to be constructed only by
skilled people with knowledge of safety
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
- 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.
This Circuit is Not a Tested Design.
It is an Idea for study
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.
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.
- Dot/Bar Display Driver
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.