3 ms·

I’m having a hard time imagining a reason that pot would need to be digitally controlled. It would be set at the factory and isn’t meant to be adjusted during u

I’m having a hard time imagining a reason that pot would need to be digitally controlled. It would be set at the factory and isn’t meant to be adjusted during use. It looks like its role is to be tuned to account for resistor tolerance in the motor’s circuit—-otherwise each board would have a slightly different current going to the motor, and different speed. If the goal is to switch between 33 and 45 digitally, then I figure you’re better off finding that switch on the circuit board and replacing it with a relay or something.

compiler-guy 6y ago
High quality turntables have a speed control and dots with strobes on the side of the platter for you to get the speed exactly right. So a non adjustable resister here is a sign of lower quality. Making it digital would be great to get the pitch exactly right.
- userbinator 6y ago
  This one is adjustable, just not very easily (it's still accessible through the hole in the bottom of the case) --- perhaps because they don't plan on it needing much adjustment other than the initial factory setting.
- smogcutter 6y ago
  The digital pot the other person posted uses 7 bits for 0-10k ohms, so it’s much less precise than a real trim pot. For most arduino type applications that’s probably fine, but if the goal is to get super anal about nailing 33 1/3 rpm exactly, and keeping it in tune over slight environmental changes, then it really isn’t good enough. I guess it would be fun to come up with some kind of feedback scheme that trims the digital pot automatically. But as a practical thing rather than a for the heck of it project it really doesn’t seem to be worth the effort over just using a pot.
  - tuatoru 6y ago
    > some kind of feedback scheme that trims the digital pot automatically Yeah, PID controllers are around, I think. (proportional-integral-differential.) Quite easy to do on an Arduino if not readily avaialble. But better to PWM-control the drive transistor directly than adjust a digital pot.
    - smogcutter 6y ago
      Good call, pwm would be the way to go. I feel like most hobby projects of mine end like this: bring home a bag of stuff from fry’s, realize while futzing with the breadboard that it’s a much simpler problem than I first thought, wind up with a bag of unused stuff from fry’s because I don’t want to drive back to Burbank to return it.

compiler-guy 6y ago

High quality turntables have a speed control and dots with strobes on the side of the platter for you to get the speed exactly right. So a non adjustable resister here is a sign of lower quality. Making it digital would be great to get the pitch exactly right.

userbinator 6y ago
This one is adjustable, just not very easily (it's still accessible through the hole in the bottom of the case) --- perhaps because they don't plan on it needing much adjustment other than the initial factory setting.
smogcutter 6y ago
The digital pot the other person posted uses 7 bits for 0-10k ohms, so it’s much less precise than a real trim pot. For most arduino type applications that’s probably fine, but if the goal is to get super anal about nailing 33 1/3 rpm exactly, and keeping it in tune over slight environmental changes, then it really isn’t good enough. I guess it would be fun to come up with some kind of feedback scheme that trims the digital pot automatically. But as a practical thing rather than a for the heck of it project it really doesn’t seem to be worth the effort over just using a pot.
- tuatoru 6y ago
  > some kind of feedback scheme that trims the digital pot automatically Yeah, PID controllers are around, I think. (proportional-integral-differential.) Quite easy to do on an Arduino if not readily avaialble. But better to PWM-control the drive transistor directly than adjust a digital pot.
  - smogcutter 6y ago
    Good call, pwm would be the way to go. I feel like most hobby projects of mine end like this: bring home a bag of stuff from fry’s, realize while futzing with the breadboard that it’s a much simpler problem than I first thought, wind up with a bag of unused stuff from fry’s because I don’t want to drive back to Burbank to return it.