Arduino Controlled Broadcasting/Turntable

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jjwharris
Posts: 189
Joined: Fri Jun 02, 2017 5:18 am

Arduino Controlled Broadcasting/Turntable

Post: # 48171Unread post jjwharris
Thu Oct 19, 2017 8:26 pm

While having moderate success with embossing, I'm still experiencing pitch issues with the stanton st150.

I've been having a think about it and I think it's possible to create a franken-belt driven turntable, PID controlled which should reduce this while producing enough torque for embossing.

The plan is to use an existing DD Sansui turntable, a 24v DC Scooter motor and a PWM controller.

My thought is;

Keep the direct drive motor as a sensor, feed the voltage output into an arduino which will compare it using the PID Library (the two known constants would be the voltage created at 45 and 33rpm)

The voltage generated from the arduino would be fed into this motor controller here replacing the supplied pot.

The motor is going to be this

There is an example of someone doing something similar on youtube here

The pulley would be a o-ring which attaches directly to the existing direct drive motor.

The brushed motor may need some sort of filtering, and I'm sure some acoustic isolation will be in order, the motor does sound very quiet from that youtube video though.

I'm wanting to push ahead with this, but am looking for the pitfalls before I begin.
Record Lathe Embossing Supplies - http://www.supplies.johnnyelectric.co.nz/

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markrob
Posts: 1623
Joined: Wed Nov 28, 2007 1:14 am
Location: Philadelphia Area

Re: Arduino Controlled Broadcasting/Turntable

Post: # 48172Unread post markrob
Thu Oct 19, 2017 11:16 pm

Hi,

Sounds interesting. Some things to consider:

Just go with PI rather than PID. The D term is not needed unless you want to maximize closed loop bandwidth. In this case, you don't want a fast responding loop. You just want the controller to reach the setpoint with no error. The I term insures that. The P term keeps the loop from hunting. A closed loop bandwidth of 3-5hz or should be fine here (implies a ~1 second settling time).

Not sure if the DD motor will work well as a tach feedback device. Might need to look at the output with a scope to see how much ripple is present when you spin the platter. Especially at the low platter speeds you will be using.

If you are using the Arduino ADC to sample the tach, keep in mind its only 10 bit (on a good day). Not sure if that's enough resolution.

The Arduino PID/PWM libraries are not the greatest. For example, I've found that the PWM is pretty bad due to high timing jitter. That's because the implementation allows a great deal of flexibility as to pin assignments. So they don't use the PWM hardware output directly. Not a issue with a simple application, but it might be too loose for this situation. Also not sure how high the PWM frequency can be set and the resolution (may only be 8 bit).

Are you planning to go with a simple single FET driver for the motor? If so, you can run into some loop tuning issues since that makes drive single quadrant (can only source power to the motor). In this mode, the ramp up rate is much faster than the ramp down as the motor will coast with no power applied. Not a big deal as long as your closed loop bandwidth is low enough.

Hope you find that useful.

Let us know how this all works out.

Mark

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fredbissnette
Posts: 383
Joined: Tue Oct 11, 2016 5:38 pm

Re: Arduino Controlled Broadcasting/Turntable

Post: # 48208Unread post fredbissnette
Tue Oct 24, 2017 1:04 pm

i bought a 150 and that did not work

i bought a 1200 and that did not work

i bought an sp10 and that almost worked


i bought a rim drive broadcast deck from the cbc(canada) and that works great

you need a lot of tourque and i find the rim drives with the really big motors ie the rusco/mcurdy/gates decks work ok
Instagram @styluspressurerecords

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