# MAKE: Experiment 4

Discussion in 'General Electronics Discussion' started by nyancatvsghosthead, Aug 13, 2012.

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Jan 7, 2012
Last edited: Aug 13, 2012
2. ### davennModerator

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Sep 5, 2009
So what specifically is the problem ?

Do you have a link to a schematic or can you post one
so that us guys dont have to go searching ?

cheers
Dave

3. ### CocaCola

3,635
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Apr 7, 2012
You might be well beyond the 2mA metering range, have you tried the 20mA or 200mA setting? Set the pot to the middle for your initial reading, not all the way to one side or the other...

If nothing happens you might have popped the fuse inside the multimeter...

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
I've just looked at your video.

You can do a number of things to help us, but the first is to say at each point what you're expecting and what you see.

For example, instead of saying something about "legitimate results" say "I am expecting a reading near 2.00 and I get 0.00".

It looks like the circuit consists of your batteries, a fixed resistor, and a potentiometer in series.

I imagine the aim is to see the current change as you rotate the potentiometer.

If you see zero all the time (flashing between 0.00 and -0.00 really means zero, there's not real significance to that) then it's almost certain that you have made a mistake.

It looks like you're using alligator clips to hold wires together, this isn't a good idea. Get pairs of alligator clips and make short leads. In this circuit, you should have 4 of them (8 alligator clips = 4 cables).

Use these cables to connect :

* from the battery to the fixed resistor,
* from the fixed resistor to the pot,
* from the pot to the meter, and finally
* from the other meter lead to the other side of the battery.

Then you should be able to have your hands free to turn the pot

It is possible the pot is faulty. To check this, remove the pot from the circuit by connecting the 2 alligator clips that go to it together.

Also check that your fixed resistor is between 1000 ohms and 4700 ohms using the resistance range on your meter (before you connect it into the circuit) just in case you've picked the wrong value. I don't know what value you are supposed to use, but in this range you'll get a small number of mA which is probably what you want.

CocaCola's suggestion of checking the meter range is also a good one, although I must admit, I thought the meter was reading 0, not over range.

1,114
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Aug 13, 2011
If you're using the 6V battery pack, 1k fixed resistor and 2k potentiometer the experiment prescribes, your current readings should range from 2mA to 6mA or a little less as your batteries weaken.

It would help if you would include any relevant figures when you ask these questions. For example, this is figure 1-64, the one you're currently using.

http://examples.oreilly.com/9780596153755-files/mkel_01/mkel_01_64.pdf

Last edited: Aug 13, 2012
6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Thanks. I was relying on what was (accidentally) shown in the video.

1,114
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Aug 13, 2011
I know Steve. You did pretty good figuring out the intent of the experiment with minimal clues.

Nyan, you should get some spare fuses for your meter (5mm X 20mm 315mA). You'll need them eventually if not now. Littelfuse 216 is a good model as is Buss S501.

Last edited: Aug 13, 2012

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Jan 7, 2012
I'll take your spare fuses recommendation. Yes, I'm supposed to measure the amperage of the circuit. It always says "0.00" regardless of what I put. I measure other things with the multi-meter and it doesn't say "0.00" at all. Did I blow a fuse in my multi-meter? But yes, I'll post a picture of the schematic pretty soon. I redid the experiment with jumper cables and it does the same thing. Thank you so much for helping.

Help appreciated, Nyan

1,114
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Aug 13, 2011
Review the information regarding measurement of DC current on pages 25-27 and fuse replacement information on page 32 of your meter manual. There are some warnings not to connect the meter in parallel with a voltage source. This is how you blew the fuse.

The genius(es) that wrote the meter manual neglected to include any instruction on fuse testing. You can test it after removal using one of the resistance scales but if you've failed to get a current reading in this experiment with the meter set on 20mA or 200mA, that's good evidence that the fuse is blown or you have the circuit connected wrong.

Last edited: Aug 14, 2012
10. ### CocaCola

3,635
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Apr 7, 2012
And here is a link to the manual if you no longer have a hard copy of it...

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Jan 7, 2012
Wait, so I think what happened was that I set the potentiometer to too high and it blew my circuit. Should I try to set the potentiometer so it isn't too high? Why does it let me measure other things besides the potentiometer? That's really weird. Anyways, thanks for the guide. I'm reading it right now.

12. ### CocaCola

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Apr 7, 2012
As I suggested set the potentiometer in the middle initially for the test...

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Jan 7, 2012
Here are the schematics and a photo of me with the experiment:

14. ### CocaCola

3,635
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Apr 7, 2012
In that picture you have the meter set to the 200 Ohms resistance measurement not milliamps current measurement....

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Jan 7, 2012
Yes, that's true. I was testing the meter to see if it would measure a resistor. It did. Does that mean that the fuse isn't broken or does it have to be amps?

I'm doing the potentiometer soon. I remember applying my multi-meter exactly as the instructions said. Thanks for the test advice.

Last edited: Aug 15, 2012

1,114
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Aug 13, 2011
The internal fuse is only used when measuring current. Other functions of the meter are unaffected when it's blown. You're going to have to replace it. Take it out of the meter and use one of the resistance settings to confirm that it's open (∞Ω). It will read the same as the leads connected to nothing.

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Jan 7, 2012
So should I set it to measure a capacitor or something like that which gives a lot of current? Why did the book tell me to measure it with the battery pack if I'm not supposed to measure it with current running through. Or am I getting the rule wrong when I say that?

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Jan 7, 2012
Also, in case it turns out okay, what does a "faulty" potentiometer mean?

19. ### davennModerator

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Sep 5, 2009
what specifically did the book say ? quote it .... you may have misunderstood what it was getting you to do ?

if you need to read current use the mA or A range on the meter

Dave