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Topic: Pararrel Pots : very odd situation (Read 1 time) previous topic - next topic

pierlooqup

Hello all,
can anyone explain me why only the odd pots in this 6-line parallel link will work?



Starting from right to left, i only get the odd ones to work, the other are completely zeroed.
As you can see i've powered the pots linking all positives and all the negatives correspondingly.
Then have linked the ground and +5v to arduino and started measuring the central pins with a multimeter (ohms). And then came the surprise. Half work, half dont.

Any clue?

myozone

overloading +5V line ? - how many ohms are the pots ?

MikMo

#2
Oct 24, 2007, 10:53 am Last Edit: Oct 24, 2007, 10:56 am by MikMo Reason: 1
What are you meassuring between ?

The centerpin on the pots and ???

If you want to use it with a analog in on the arduino board you should be meassuring Volts between the centerpin and ground. because the pots are wired as voltage dividers sending a voltage between 0 and 5 volts from the centerpin to an analog in pin on the Arduino board.

The wiring looks perfectly right.

pierlooqup

myozone : these pots are normal 10k pots
MikMo : i'm measuring between the central pots and the ground pin on the breadboard, the same as the source for gnd that goes to the first in the series of pots...

Ah.

Maybe that's why? Some friend suggested that i should ground each pot separately... that could be it?
Thanks!

MikMo

You wiring is not wrong. I made a similar setup with 16 slide pots just the other day and i just used two pieces of steelwire to connect all the grounds and all the 5V pins on the pot's and then connected these two to ground and 5V on the Arduinoboard. As far as i can see you do exactly the same.

But you should be measuring volts  not ohms as i say i my previous post.

And meassuring between the pot centerpin and ground you should read between 0 and 5 volts depending on where the pot wiper is positioned. This is what the Arduini board expects to see on an analog input pin.


pierlooqup

Quote

But you should be measuring volts  not ohms as i say i my previous post.

And meassuring between the pot centerpin and ground you should read between 0 and 5 volts depending on where the pot wiper is positioned. This is what the Arduini board expects to see on an analog input pin.


Ah... i thought the central pin outputs a resistance from 0 to 10k according to the knob's position... how noob i am.
And anyway - i tried reading the cental pins on arduino of course and i get the same...
Working pots give me from 0 to 1028 or something, while the others send either a constant zero, no matter how i turn them  - or totally random values, the ones you get when you read where a free cable is plugged...

MikMo

Thats very strange. Are you sure your soldering to the pots are ok?

I had similar problems with crazy values, from just one pot until i discovered that the +5V was not connected to the pot.

You could try to swap one working pot with one that is not working and see if it makes any difference.

A pot could be defect, but of course 3 defect's is not very likely.

pierlooqup

I can't be 100% sure about the soldering. As i keep on saying it i'm a total newbie...
So i will do this. I wil check the soldering and maybe try every single pot before resoldering again...
Takes time...but i'll do it.
Thanks for your help - i'll report here as soon as i'm done testing.

myozone

You should have no problem with 10K pots - check you have 5 volts across each end of each pot, ideally on the metal contact of each pot not the wire (checks the wiring ;) )

pierlooqup

Ok,
after an in depth check of every and each of the pots i found out that they're ALL broken somehow. Lesson i've learned is, i will never ever buy cheap components again.

Excuse me for wasting your brain-time!
Thanks again everybody anyway...

myozone

Probably the wiper (centre pin) is not touching the carbon track inside the pot

MikMo

Some very cheap pot's will go apart inside if you heat the pins a little too much when soldering.

Daniel

#12
Oct 25, 2007, 11:14 pm Last Edit: Oct 25, 2007, 11:16 pm by Daniel Reason: 1
Quote
Then have linked the ground and +5v to arduino and started measuring the central pins with a multimeter (ohms). And then came the surprise. Half work, half dont.

Any clue?



two ideas here:

- if you are measuring resistance while the circuit is powered, you won't get accurate readings. The meter puts out its own current for making  resistance measurements, and the circuit current will interfere.
- What you should really do is use a DC voltmeter to measure the wiper voltage of each pot, with the pots powered by 5V as you have it wired.

D

pierlooqup

Quote

- What you should really do is use a DC voltmeter to measure the wiper voltage of each pot, with the pots powered by 5V as you have it wired.


Thanks Daniel, but as i said above i found out all the pots were broken... ;)

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