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Numark PT01 Scratch Bluetooth Plate
A custom faceplate for the Numark PT01 scratch that allows to add a bluetooth audio device to the unit.Other
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I liked the idea of the ScratchToys sound plate, but found its price a tad steep for my taste, and also availability was quite limited these days. So decided to create my own variant of it.
Building this project will get you a Bluetooth/SD Card/USB reader module built into your Numark PT01. My primary use case is to allow the looper app on my mobile to stream its audio without a 3,5mm cable to the PT01 (#lookMomNoCables!) But is also offers media player capabilities from SD card or Bluetooth, so you could even put your beats on let's say an SD card and it effectively turns your PT01 into a truly independent one-in-all mobile scratch solution.
The Line In connector still works as well as it's input is routed through the BT module and can be selected as an input. I cannot tell if the USB port still works, but I would not see any reason why it wouldn't.
Materials and methods
Just print the plate. Be ready to use a file, as I was not able to get the openings for the stock USB, line in and gain knob 100% accurate. It's however close enough. (Feel free to contribute a patched version of the SCAD and accompanying STL if you want to make this piece more accurate.)
The bluetooth module I used is the one available here:
It is somewhat tight, as the width of the BT PCB mounting rack is about 5mm wider than the space available between where the screws are mounted in the PT01 chassis. It how ever does fit, and the screws from the BT PCB mounting rack even fixate that way nicely.
I used JST cables and sockets to wire everything clean. The mini stripboard with the 3 JST sockets is just my version of an Y-Cable to get an additional power socket that I can hook the BT part to. You can alternatively wire this all up directly via soldering, but using the sockets keeps things modular (and makes you look more pro, hehe).
You must also do some very minor soldering work, as you need to create a ground loop isolator to separate the BT module from the rest of the circuitry. Otherwise you will get very noise audio - especially once the bluetooth data starts flowing. You can find a good showcase of the problem as well as the background explanation AND the solution to it in the following video.
Don't be scared if you are not an electronics geek - it's really ultra simple. It's the thing on the small stripboard on the top left above the BT module on the pictures. Really nothing fancy, consisting of three elements only.
Just make sure you get the isolator unit, that outputs the voltage fitting the bluetooth module you got. My setup is based on 12V. The guy in the video uses one that needs 5V. So you must get the right isolator and you must adjust the values for the inductor and the capacitor to match for the isolator unit. Here's the overall list I used:
Isolator: Murata NKE1212SC (from 12v to 12v - just pure isolation, no step down to 5v)
Capacitor must be 0,47µF
Inductor must be 68µH
In case you get an Isolator from a different vendor or one from Murata with different output voltage, you must check the datasheet of that unit to get the correct Inductor and Capacitor values.
The stock power cabling is
Power Module -> Stock USB PCB
afterwards you have
Power Module --> Y-Cable/Board
Y-Cable/Board -> Stock USB PCB
Y-Cable/Board -> Ground Loop Isolator -> BT Module
Audio Cabling itself is conceptually just making the audio from line in take a detour. So stock cabling is:
Aux In -> Sound Board
and when you're done, you have wiring from
Aux In -> BT Module Input
BT Module Output -> Sound Board
Note you must also disconnect the ground (black in the middle) from the audio cable that comes from the red aux-in socket. Otherwise you (re)create the ground loop that the Isolator is meant to prevent.
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