1 Megohm Potentiometers

We’ve got three “1 Megohm” potentiometers, that we were planning to use to find arm position. If 1 Megohm = 1,000,000 Ohms will these work? I was under the impression we needed 100K potentiometers, which by my reasoning means we are a factor of 10 off. If these will not work, where can we get pots that will work today?

FIRST suggests that the POT should not be more than a 100k Ohms. Yours is 10 times more, i would suggest that you use a 100K one. Too much resistance in the circuit will come out as a value of 0 voltage to the RC. As in, if there is only 0.5 volts flowing through the RC then it reads it as 0 Volts. It is a good idea to stay near the 100 K mark.

You need 100K pots,

We used Bourne product #3540S-1-104

http://www.newark.com/NewarkWebCommerce/newark/en_US/endecaSearch/partDetail.jsp?SKU=01F8344&N=0

I think its also available at mouser (www.mouser.com)

You do not need 100K pots, but you may not have very much luck with 1M Ohm pot. The only way to really know is to try it. You only need 100K pots on the OI, we use a lot of 10K pots on our RC without problems.

If you needs the pots quick Radioshack carries 100K and 10K in their retail stores.

Just to clarify-

You may use any value pot on the bot, assuming everything else is equal. Some values work better then others. 95 uses 10k’s mostly. It’s a common value among the pots we like to use. 100k works well to.

100k pots work on the OI best, but it is no longer a legal matter what you use. IFI has posted a range of values that it suggest you stay in. I believe it starts at 250, and goes up to 10k, but don’t quote me on that. I would stick with 100k for the OI. All the pots in the joysticks are 100k.

I would suggest you go with a 10k - 100k pot. You can pick them up at radio shack, although they will be pretty cheesy. If your not worried about the quality to much, you can get some Tuesday. I would go with those, and order some higher quality pots as a replacement if the radio shack units turn out to be to cheesy.

-Andy A.

I’ll second the vote for 100k pots on the OI - we’ve had strange troubles with other sizes. I can’t say anything about the RC, however. We just started with 100k and stayed there.

Bjorn,
The 1M pot will give some indication of change but the input resistance of the RC and the pot value interact. The 1M may show some change but it might not be linear. (i.e. values per degreee of rotation will vary from one end of the pot to the other and may stop changing at some point) If you need linear, accurate data, stay with the 10K to 100K values.

Depends on the input impedance of what you are connecting to of course, but Al reminds me of something here - don’t forget pots come in linear taper and logarithmic taper. Make sure you get the one you want, and don’t buy the cheap ones, they can be really pronounced in what Al is saying above.

Also, at 5V, a 1megohm potentiometer is only drawing 5uA (5 millionths of an ampere), unless I’m terrible at math. From my limited knowledge of E&M, at currents that low, I would be worried about interference from other electrical components. Jumping on the bandwagon, I’d go with 100k or 10k pots to get a reliable signal.