DIY Turntable

You always wanted to be a Disc-Jockey. You know nothing about beats, delays or mixing but, damn, scratching is like the coolest thing ever invented!

If this is also your case, follow this instructable to build a low-fi DJ set: the DIY Turntable as featured on Gizmodo and Engadget, and take the chance to recycle your old cassette player into a new cool instrument.

Step 1: Materials

Minimum:
- Cassette player (better if it's an old one)
- Wire and wire strippers
- Prototyping breadboard
- Soldering iron + solder
- Screwdriver
- 5 to 9V battery with battery holder
- Some kind of variable resistor or potentiometer

Advanced:
- Arduino with its USB cable
- IRF540 Mosfet (transistor)
- 5 LEDs
- 5 220ohm resistors (brown-red-red)
- one 1kohm resistor (red-black-brown)
- Computer cooling fan
- Box or some kind of enclosure

This project is divided in two parts. By doing only the basics you’ll be able to control the speed of the music  without even having to touch an Arduino or write a line of code. Almost zero budget and quite fun.

If you decide to follow to the advanced part, you’ll be able to have the pc fan act as a turntable (although it won’t be real scratching because the gears of the walkman won’t let you play backwards). You'll have total control over the speed of the music and will add whatever effects you like, like the LED indicator.

So, let’s get started!

Step 2: Walkman Hacking

The core of this project is the following: In a cassette player, there’s a small DC motor that spins the tape. It’s powered by a battery that provides a constant voltage. Our goal is to supply our own voltage to the motor: higher than the battery to speed up the song or lower to slow it down.

Opening
Start by taking off the battery. Unscrew all the screws on the back case and inside the battery place and remove the case. Do it carefully because some parts like the volume gear are loose and you may have to place them again. Take a picture or remember where everything is.

The tricky part
Once you see the guts of your old player, you’ll have to find the two wires (red and black) that provide voltage and ground to the small, round-shaped DC motor that will usually be on the right side. If you’re lucky you’ll see the points where they are soldered, otherwise you’ll have to cut them.

To check they are the ones we’re looking for, press the play button and try to apply some volts on this wires by connecting them to your battery. If the song plays, you found the right spot!
Now solder your own black and red wires to where the original ones are soldered, or cut the original ones and attach yours. Leave your wires quite long to have room to play.

Close it
We’re almost done. Find a place to pass your wires once the case is closed. Many players have a hole for DC-In that’s very useful for that. If yours doesn’t you might have to drill yours, or pass them through the space for the battery.

Finally, put everything in its place again, close the case and screw it on.

Step 3: Be Creative!

Now, your walkman is hacked. Insert your favorite tape, apply whatever voltage you want to the wires and, if play button is pressed, the song will play faster or slower. Be aware that there’s a minimum voltage to start the motor, and a maximum you shouldn’t go over if you don’t want to burn the circuitry.

But the fun thing is to have control, and the easy way to do it is with variable resistors. Start with a simple slide or knob potentiometer like the one in the image.  After that, you can try with more interesting stuff, like placing a photocell between the positive wires of your battery and the motor (sorry, I didn't have one to show you!). You'll probably need more power, but eventually you'll be able to play your walkman like a theremin.

These cheap parts will change their resistance depending on different inputs and allow you to control the walkman with a simple analog circuit.

So here’s my challenge: Be creative and invent your own controllers!

Step 4: Digital Wiring

If you, like me, are more comfortable with digital electronics, here’s how I wired everything up.
The fan positive wire is connected to pin A1 in the Arduino, and the negative one is connected to ground through one 1k ohm resistor (it acts as pull-down).
The walkman is connected to the digital pin 6 of the Arduino using an IRF540 transistor.

Notice some important things:

- You’ll need to have a battery holder with a jack to plug it to the Arduino. This way can we power both the Arduino and the Motor. 

- We're only using the red and black wires of the fan, the other is for control but we don't need it in this case. Some newer models maye even have more wires.

- The fan is plugged directly to the analog pin of the Arduino, which is something you should never do because you could fry it, if it reads more than 5V. I did it because I previously tested the fan and found I couldn’t generate more than 2V by spinning it manually. So, if you can, test it too.

Step 5: Arduino Coding

The code basically performs one task: read the input from the fan and map it to a proportional output to the walkman. It also smoothes the readings from the fan, since they are quite unstable.

Download the attached file, compile it and upload it to the Arduino (is it your first time? check out the guide )

When testing it, you may find that you have to tweak the ranges for both the input and the output, since they will change depending on your hardware and battery. Try adjusting this 3 constants:

- minV
- maxV
- maxFan

Step 6: Make It Look Nice!

When everything works, you can add the LEDs for some extra eye candy. Solder black wires to their short legs and red to the long ones. Then plug the negative (black) to the ground line of the breadboard with a 220ohm resistor inbetween. Their positive legs should be plugged directly to digital pins 8, 9, 10, 11 and 12 of the Arduino.

Build a nice enclosure from whatever material you have available and attach the devices to it. Since mine was cardboard, I fixed the cassette player and the cooling fan with their own screws, and it was easy to drill holes for the wires. You’ll have more work with more sturdy materials, but it will look better.

Fix the battery, breadboard and Arduino inside of the box and wire everything up again. Plug the battery, choose a tape and... make them dance!

You can now play with different tapes and see how vocals, instruments and rythms are distorted by the changing speed in different genres of music.