I'm DMM Deficient

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Kwote
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I'm DMM Deficient

Post by Kwote » Tue Jul 01, 2008 11:30 pm

that's right. i'm a retard when it comes to using the DMM.

somebody help me!

i can build the kits but to be honest i never really tested or calibrated. just plugged and prayed. it's worked out but i can't keep this up.

i sorta got the basic concept figured out but i can't seem to get accurate readings.

in short: goddammit.
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Muff Wiggler
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Post by Muff Wiggler » Wed Jul 02, 2008 12:37 am

what's the trouble? I have a $9 DMM I got at Radio Shack, pretty easy to use. Select the type of stuff you want to measure, and the range of the value you expect to see, using the big dial.

Two leads come from it. You touch (and hold) one to ground somewhere, and then touch the other to the point on the board you need to measure, or the calibration point. See the value on the screen.

That's for most measurements. For current draw, you basically cut the power cable, put the DMM in between in, one lead towards the power supply, one towards the load (module).

Perhaps you aren't grounding it when measuring at a calibration point?

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Kwote
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Post by Kwote » Wed Jul 02, 2008 1:40 am

i got 15v measured but i couldn't get consistent results.

i put it to common on the pcb and it helps but still not getting the numbers i'm looking for.

it says to set RT1 on the Dual Filter to .644 or somewhere around there and the closest i'm getting is .200 somethin.
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Muff Wiggler
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Post by Muff Wiggler » Wed Jul 02, 2008 1:58 am

are you testing at TP1 or testing at the trimmer? the RT1 trimmer sets the amplitude..... you measure it at TP1 though.

One probe on TP1, one probe at common. If your DMM doesn't auto-switch, then make sure it's the ground probe that goes to common.

Also, make sure you set your DMM to the right range. You should set it for '1V' (or as close as you can, maybe 2V or 5V is the best choice).

hope this helps!

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Kwote
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Post by Kwote » Wed Jul 02, 2008 3:12 am

i think i'm gonna chalk it up to having a shitty dmm.

i'm gonna buy a cheaper bulkier one with a meter instead of a lcd display and see if it's more dependable. fuckin radioshack givin me headaches.

i think i got within the ballpark for everything though but this fuckin thing ain't consistent at all.
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Muff Wiggler
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Post by Muff Wiggler » Wed Jul 02, 2008 3:23 am

Measure your other Dual Filter - do you get the same wonkiness, or is it more stable?

Maybe something is goofy in the new build and the voltage at the test point is fluctuating?

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Muff Wiggler
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Post by Muff Wiggler » Wed Jul 02, 2008 3:28 am

Oh yeah - don't buy a MM with a needle meter. Buy one with an LCD. Kinda hard to fine-tune something to 0.644v or whatever using a needle meter.

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Kwote
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Post by Kwote » Wed Jul 02, 2008 10:50 am

Muff Wiggler wrote:Oh yeah - don't buy a MM with a needle meter. Buy one with an LCD. Kinda hard to fine-tune something to 0.644v or whatever using a needle meter.
yeah. sorry my mind was off. i just meant one with a dial for selecting the settings i want.

the problem with the radioshack one is i have to scan through with a button and it only brings up 3 choices in the Volt section even though the manual suggests there should be more.

atleast the ones with the dial have a bunch of in your face options and i can go right where i need to go. 2v for the +15/-15 reading and 600v for the .644 reading.

just mad cuz i spent 30 bucks on that stupid radioshack one thinking it would be nice to have something compact . :doh:

the new filter works just as great as the last one so i don't think there's anything wonky but i'll test the other just to be extra sure.

thanks man.
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Kwote
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Post by Kwote » Wed Jul 02, 2008 10:53 am

ps: i started using the DF as a simple two input mixer with both sections in LP mode, freq full CW. it's very awesome.
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Post by futuresoundsystems » Wed Jul 02, 2008 12:25 pm

...get an analogue one....
Seriously, I find I use my trusty, "non-powered" analogue multimeter more than my digital. The DMM I have often gives wonky results, sometimes very correct, others all over the place. I always check it with the analogue just in case.
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Kwote
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Post by Kwote » Wed Jul 02, 2008 12:31 pm

futuresoundsystems wrote:...get an analogue one....
Seriously, I find I use my trusty, "non-powered" analogue multimeter more than my digital. The DMM I have often gives wonky results, sometimes very correct, others all over the place. I always check it with the analogue just in case.
hmmm. yeah. not a bad thought. i'll get a cheap one of both and contrast/ compare.
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Cybananna
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Post by Cybananna » Wed Jul 02, 2008 9:28 pm

I just got a cheap one from home depot that works fine. Make sure you're keeping good contact with the probes. that can cause jumping around. I did notice it being very stable when adjusting the trimmer on the dual filter and was able to get the actual .644 value.

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Post by Cat-A-Tonic » Wed Jul 02, 2008 9:37 pm

Mine is an AND AD-5528
It has the LCD readout and the big dial with ohms. volts, and amperes.
I think it cost me about $40.
It is very portable and really accurate.
It is more accurate than my father in law's DMM's and he was an electrical engineer.

Sometimes a point will fluctuate in voltage if there is another spot that needs to be trimmed first.
Fiddle with the trimmers a bit more and you may be able to tame it.

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Post by felix » Fri Jul 04, 2008 11:27 am

I'd say have both.

I generally used my analog one for everything (until it broke) but the circuit short indicator ("beep") on the DMM was indispensable for debugging why a circuit wasn't working.
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Post by Bricks » Fri Jul 04, 2008 1:02 pm

fuck. Im such a gearslut I thought this was going to be about Deluxe Memory Man

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Post by whomper » Fri Jul 04, 2008 2:14 pm

A DMM is one thing you would want to invest in if you're doing DIY.
It's invaluable in making sure that what you built is actually up to spec.

I found the cheapest FLUKE off ebay and never look back. It is rock solid and stable and always a consistent measurement device.

It also helps you trace built errors, test resistor values (instead of reading their colors), measure up capacitors, test LEDs etc.

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Kwote
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Post by Kwote » Fri Jul 04, 2008 6:50 pm

yup. it seems it's one of those things where you get what you pay for doesn't always apply.

can't wait to get a cheapo one next friday. i got a mixer to build goshdarnnit
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