Log to lin conversion

Hello everybody,
my problem is that I accidently bought logarhytmic pots instead of linear ones. Is it possible to make a hard- or software based conversion in order to get a linear behaviour ? I found a lot of information about how to convert a linear pot to a non-linear in the internet, but not the other way. If was great if somebody could help me out.

Regards,
Andreas

No.

Why can’t I use a software based lookup-table ? I little more detailed answer was nice. As I remember the internal resolution is at 8 bit and the ADC works with 12bit. Please correct me if I am wrong. With a log pot I’d have about a 1/10th of the available 12bit resolution in the lower half of the taper what would be 4096/10 = 409 steps. Making a lookuptable would mean (for the lower half) a conversion between 409 steps to 128 steps what would possible for what I think. Or are the controls handled at a higher resolution than 8bits ?

The ADC on the AVR is 10-bit, but you have to jump through many hoops to get there (in particular: freezing the CPU while a conversion takes place). With other stuff happening on the chip while a conversion take place you get a bit less than 8-bit. Not enough to get the 7-bit linear resolution that the Shruthi needs. You might try filtering/averaging the ADC values to fake more resolution, but that’s a lot of work, which might overload the CPU or flash memory size.

vs

spending less than 5€ on the right parts.

okay, tank you. Now I understand it better. I am a software engineer and started to read the code but it’s hard to see every aspect. Then I’ll choose to buy some new pots even if they are way more expensive than 5Euros xD It’s about 28 Euros + the 20 EUros I already spent in the wrong pots. Or can you tell me where I can get 28 the pots such cheap here in Germany/Europe/elsewhere ? I bought some ShrutiXT pcbs, so they must be the correct print version with a height of 17mm for fitting into the enclosure together with the other parts. I tried to find them on aliexpress but wasn’t able to find them.

Hm, i bought my pots for the XT at the big R in Germany. And the knobs at Conrad…

Thanks nightworxx, I’ll have a look there. I am searching on Alibaba all the time now and finally found a supplier. Unfortunately he only sells lots auf 500 for 128 Euro. I asked him if he sells a lot of 100 too and I wait for the answer now.

Maybe you can find some people to share a group buy.

I recently found a seller on aliexpress. The article wasn’t in the shop, but he has it and put it into the aliexpress shop for me after I mailed him :slight_smile: If anybody else needs some here is the link:

http://www.aliexpress.com/item/BELLA-09-Model-0932n-potentiometer-single-vertical-joint-potentiometer-B103-B10K-20MM-D-shatf-handle/32443370984.html

I paid 30€ including shipping to Germany for 100 pots.