A more useful device for your +/- 8% pitch, would be an Arduino controlled strobe. You could run it both ways, either tune the recording speed up/down to suit your listening, and then adjust the strobe to measure, or else set the desired exact pitch on the Arduino, and adjust the turntable to match it via the dots.
Probably much easier for a beginner to program, too.
One problem you will face, is that the Arduino you are using, has a ceramic resonator for a time base, instead of a quartz crystal. So you can not expect great accuracy from even the best software measurement method.
I don't think Arduino can in any way (not even through the stroboscope) regulate the motor speed. The motor is integrated on the motherboard. If it could be done I would have solved a lot of problems. To manage motor speed through Arduino, I'll try
to replace the slide potentiometer with a 255 step digital potentiometer and memory recall.
About Arduino Hardware,
I tested three other models:
Arduino Nano AMTEL MEGA 328P (works fine)
Cheap Arduino Nano AWGA328P (super slow)
Seeeduino Xiao (works well)
Cicciobit,
I hadn't realised that you already had a dedicated frequency counter to measure the frequency - I thought you were going to have to try and write a sketch to use your Arduino to do it.
Just to avoid any confusion, that figure of 262.08 kHz appears twice in the service manual.
One is a fixed frequency generated by dividing the crystal oscillator frequency, used by the strobe LEDs.
The other is variable with a trimmer pot as you have pointed out.
Yes, I have the frequency meter. I'm going to put in a larger touch display and digital pots / trimmers to digitize this turntable as much as possible. I will use the Menus and submenus to modify everything digitally I will also need digital relays to replace the two switches that I put years ago to enable and disable the quartz lock and the switch located in the center of the potentiometer. slide (green led in the center) which serves to bypass the potentiometer and set the frequency for zero speed%. Maybe I'll make it in 10 years
