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

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...

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.
stevekrawcheck (author)  steveastrouk4 years ago
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...
Here's a circuit of one channel.
Copy of new-1.jpg
stevekrawcheck (author)  steveastrouk4 years ago
Thank You! I'm in Las Vegas, NV, USA. More later...