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Forum Index : Electronics : ohm meter
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kingw Newbie  Joined: 07/03/2010 Location: United StatesPosts: 23 |
howdy gents, my friend has some schematics and was curious what he would need to alter to change this meter to top out at 15 ohms. i figured it might be a cinch for you guys, any help is appreciated. the file looks like it has some little spelling errors etc, and if the key is in the diagrams at the bottom any basic explanation is nice. thanks! b 2010-11-20_054741_LA9IHA_Milli.pdf -kingw |
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GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I am all for meters, but I find that anyone who is building power supplies will already have a power supply of some sorts, and a volt meter and amp meter. I use a power supply capable of supplying at least 1amp. connect the unknown resistance across it with some clip leads. accurately measure the current through the resistance, and the voltage directly across the ends of the resistance, not on the clip leads. R=V/I Can't get simpler than that. Works down to within the accuracy of the volt meter, and amp meter. If resistance of less than 1mohm is needed, then just use a higher current. Most digital multimeters read down to 0.1mV. Overcomes lead resistance measurement errors as well. Gordon. become more energy aware |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5016 |
Hi kingw I would change the R3 resistor to a single 18ohm resistor, instead of the 3 12ohm and 1 18ohm resistors in parallel. Thats should work, but I would also put a 1k resistor in series with the meter, so it doesn't burn out if you sort out the RX resistor. But I think a better way to go would be buy a cheap digital multimeter. A $10 multimeter will have a 200 ohm range, and will measure up to 15 ohms reasonably accurately. The test leads will have some resistance, about 0.3 ohms, but once you know this, just subtract it from the meter reading. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| kingw Newbie Joined: 07/03/2010 Location: United StatesPosts: 23 |
Thank you gents! -kingw |
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