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indicator lights to show voltage.? Answered

I live in the jungle in Thailand, in the morning the electric supply is only 145 volts till 8 am at that voltage many things do not work mainly the water system. During the day the voltage is adequate and things work, in the evening we are back to 145 ish. I want a light panel system so that my wife and I can easily see whether to use the water system or not. So red, yellow and green indicators to show red 145, yellow 170 and green 185 or round about. The display to be constant, I have Fluke meters but they all time out after a while. I can source most electronic components.



9 years ago

I'd get a say an, 18V transformer, use that to create a 5V DC powersupply to drive a bar-graph meter made with an LM3914 chip. The 3914 drives 10 LEDS. The supply would have three components, a rectifier, a reservoir capacitor (1000uF), then a 7805 regulator. The regulator will get hot in use, so make sure you put a heatsink on it.  You get 5V AFTER the regulator, but, from your numbers, the input to the regulator is going to vary from ~10V up to 18V

The datasheet for the LM3914 has all the example circuits you need to put something together.

You'd scale the input to the 3914 with resistors, taking the RAW input to the 7805 regulator as your input to the 3914, through a couple of resistors.

The application circuits in the datasheet show a nice "offset zero" scale design which is perfect for you - you want 140V to be the first LED lit, and 220V the last. You can select which colour LEDs are best for you.