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What Pot? Paddle Knobs.

Posted: Wed Sep 26, 2012 12:13 am
by toxibunny
Say I want to make a couple of old-school paddle controllers. I'd need a couple of proper knobby potentiometers like the ones on this page: http://www.bebek.fi/kauppa/tuotteet.php ... hma_id=280 (apologies for the language, btw. 'akseli' is 'axle', and 'kiinitys' is 'connector', or something. it's a local shop.)

Which ones though? I'm guessing a linear rather than a logarithmic one, but how many Ohms? Why are some of them 2-way?

Also, would it be better to have the ADC chip inside the controller, then a long digital wire to the Pi, or a long wire from the pot to the ADC?

Re: What Pot? Paddle Knobs.

Posted: Wed Sep 26, 2012 12:17 am
by toxibunny

Re: What Pot? Paddle Knobs.

Posted: Wed Sep 26, 2012 5:58 am
by morphy_richards
It doesn't massively matter what rating of pot because you will be adjusting a voltage which will be a ratio of the resistance between the first and middle terminal and the middle and the last on the pot (using the voltage divider idea) (edit - not too high a resistance as you may limit current too much 10k or so should be fine)
I personally would do my adc at the source to minimize interference on the line as digital signals should be less susceptible. You might want to get shielded cable too.
2 way ones have 2 pots in one.. I think.... Don't know why though.

Re: What Pot? Paddle Knobs.

Posted: Wed Sep 26, 2012 9:10 am
by Burngate
Logarithmic comes originally from neolithic audio - your ears are near-as-damit logarithmic.
The main use for 2-way ones is stereo.

With the pot on a long wire to the ADC you only need the three wires for the pot, but there's going to be noise / interference.
With the ADC right by the pot and a long digital cable, you'll need to send power as well as the digits

In the long-analogue scenario, if you've got more than one pot you'll need an extra wire for each extra pot
In the long-digital scenario, you still only need the same power and digits wires however many pots you want

Re: What Pot? Paddle Knobs.

Posted: Wed Sep 26, 2012 10:23 am
by morphy_richards
Out of curiosity which ADC are you using - is it an MCP3008?

Re: What Pot? Paddle Knobs.

Posted: Wed Sep 26, 2012 12:25 pm
by toxibunny
I'm still unsure on the ADC - I'm hoping to find one on that site, but it'll need to be 12/13 bit at 60samples per second to be smooth on an HDTV...

Re: What Pot? Paddle Knobs.

Posted: Wed Sep 26, 2012 12:33 pm
by morphy_richards
Let us know how you get on. I'm on the lookout for a multichannel one that allows several to be used at the same time. I've got some MCP3008s on order but I heard somewhere else that the SPI bus can only support one for some reason (?)

Re: What Pot? Paddle Knobs.

Posted: Wed Sep 26, 2012 3:20 pm
by Burngate
toxibunny wrote:I'm still unsure on the ADC - I'm hoping to find one on that site, but it'll need to be 12/13 bit at 60samples per second to be smooth on an HDTV...
12/13 bits - 70dB - then you definitely want to keep the ADC near the pot(s) to avoid noise! Also I'd be looking at better pots - those look like carbon track: I'd try conductive plastic