# What is the total resistance of many test points?

Discussion in 'General Electronics Chat' started by cdynasty001, Oct 17, 2016.

1. ### cdynasty001 Thread Starter New Member

Oct 17, 2016
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Say I have a box with unknown inside. I'm asked to figure out the total resistance by only using these spikes with a multimeter/analog meter. How would I go about doing this?

2. ### Dodgydave AAC Fanatic!

Jun 22, 2012
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Stick your meter on Ohms and measure between the pins, see whichever is the highest value.

3. ### mcgyvr AAC Fanatic!

Oct 15, 2009
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Total would entail you measuring resistance across each pair of pins and summing all the readings of each of the pairs..

4. ### cdynasty001 Thread Starter New Member

Oct 17, 2016
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So would I write a chart? As in pin 1 to pin 2, pin 1 to pin 3 and so on. And add up the readings? Or simply find the highest value?

5. ### ErnieM AAC Fanatic!

Apr 24, 2011
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You show 16 pins and do not define what "total" means.

To determine pin to pin resistance measure between pin 1 and the remaining 15 pins. 15 measurements total.

Then repeat for pin to to the remaining 14 pins (you already have pin 1 to 2). Repeat for the remaining 14 pins.

And so on until you finish by reading pin 15 to pin 16.

Next, reverse the probes and do it again unless you are certain your unknown contains only pure resistances and no diode elements.

That is either 120 or 240 measurements, and what you do with them is entirely up to you.

6. ### cdynasty001 Thread Starter New Member

Oct 17, 2016
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Thank you. You wouldn't happen to know where I could find a circuit diagram connected to pins such as these would you? I'd like to see an example

7. ### ErnieM AAC Fanatic!

Apr 24, 2011
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Your sketch seems to be of a connector. A connector is a general use item used to connect one thing to another.

Here "thing" is intended to convey almost anything can be connected to a connector.

Thus there are no examples to share.

8. ### cdynasty001 Thread Starter New Member

Oct 17, 2016
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I realize that. It's a small box with a battery inside. Do you know of any circuits such as this that are connected to this many pins?

9. ### ErnieM AAC Fanatic!

Apr 24, 2011
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In addition, there is no way you can reverse engineer some unknown circuit by just reading the resistance at the pins.

10. ### DZRHNDS New Member

Oct 1, 2016
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And the highest one is ????

11. ### cdynasty001 Thread Starter New Member

Oct 17, 2016
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Why do you ask which the highest is? Is that important?

I'm also not sure what you're saying in your last comment. Can you elaborate?

12. ### mcgyvr AAC Fanatic!

Oct 15, 2009
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Ignore DZR... Seems they aren't aware of "forum etiquette".. And is just trying to get an answer to his problem with his welder in your post (commonly referred to as hijacking)
Or just isn't aware where he is even posting responses to.. (commonly referred to as being in la-la land )

I'm not sure what benefit you expect to achieve looking at other "circuits".. But there are THOUSANDS (millions) of circuits out there that connect to pins/connectors..
Looking at random circuits connected to pins isn't going to help you at all.. (whatever your goal is)..

So...What is your whole goal here?
Is this a class assignment?
Do you have a random box and you want to know what it does?
Did you find this in your front yard or something?

This forum is usually very helpful.. But we don't read minds and won't sit here and pull information from you..
Ask a question.. provide as much detail as you can.. be straight with us and welcome to the forum..

Then as Ernie points out in post #9 just knowing the resistance of pins doesn't tell you a damn thing about what the device actually does... Its far more complicated than that..

ErnieM likes this.
13. ### cdynasty001 Thread Starter New Member

Oct 17, 2016
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It's a class project. My teacher wants to know what steps we would do to measure the resistance and voltage. I know the first step would be to turn the power off, then measure between each pin like said above. The voltage would be all the same if connected to one battery.

14. ### cdynasty001 Thread Starter New Member

Oct 17, 2016
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Also, the admin blocked my other post saying this is the same question. It's an entirely different question man. Thanks for blocking my post.

15. ### ErnieM AAC Fanatic!

Apr 24, 2011
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Once you put a battery inside the box each and every pin to any other pin may show a different voltage.

16. ### mcgyvr AAC Fanatic!

Oct 15, 2009
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Other than "how do I pay more attention in class so I know the answers to the questions asked by the teacher?"

17. ### WBahn Moderator

Mar 31, 2012
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We know that won't work.

Consider if there was a single resistor in there in which half of the pins were connected to one side and the other half were connected to the other. This approach would yield a value that is 64x the value of that resistor.

Without knowledge of the possible circuit topologies that might exist in the box you can't divine very much information about what's in there at all. Add a battery to the mix and all bets are off.

The very notion of what "total resistance" means in this context is completely undefined.

#12 likes this.
18. ### mcgyvr AAC Fanatic!

Oct 15, 2009
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It would work if the definition of "total resistance" means to ............ measuring resistance across each pair of pins and summing all the readings of each of the pairs..
But as many of us have stated.. "total" is underfined (and the assignment is a wild goose chase/waste of time anyways... as described to us)

19. ### WBahn Moderator

Mar 31, 2012
24,071
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So the "total" needs to be penalized more?

20. ### mcgyvr AAC Fanatic!

Oct 15, 2009
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I think its 16 "pin analyzed" in this case