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How do I use the LM3914H bargraph voltmeter circuit to switch 2 amp, 12 VDC loads instead of LED's? Answered

I'm thinking either power transistors or relays instead of the LED's, but designing the actual circuit is a little beyond me. I'd actually like to build two of these and use the second to measure DC current of 0 - 20 amps, I'm thinking measuring the voltage drop across a shunt resistor...

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steveastrouk (author)2012-08-31

Get a load of optoisolators, like the ILD4

http://www.vishay.com/docs/83646/ild1.pdf - they're quad devices, so you need 3. These give you an nice, isolated transistor which can then be used to drive a relay like these 12V ones directly

http://uk.farnell.com/omron-electronic-components/g6ak-274p-24dc/relay-3a-24vdc/dp/2076390

, but don't forget the flywheel diode, and don't forget that the relay coil is polarised for these little beasties.

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Thank you! But... I'm an RV technician, and studied electronics for a bit when I was a kid (a long time ago, vacuum tubes!). I know which end of a soldering iron to hold and can follow schematics, but flywheel diode? A bit more info or a sketch would be tremendously appreciated! I wouldn't need the whole thing, just a typical segment...

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steveastrouk (author)2012-08-31

Here's a circuit of one channel.

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user

Thank You! I'm in Las Vegas, NV, USA. More later...

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