Monophonic Cassette Walkman "Mellotron" - First Look

So I've got a few cassette walkmans just lying around, doing not much. I decided to build a three-voice sample playback device. Here you can see the heart of a monophonic version. Once I build and test the three voice version, I will post schematics, pictures and video.

Tape-o-tron

Video URL: http://www.youtube.com/watch?v=d2DL9WoIGtM


A monophonic MIDI keyboard-controlled cassette player with the following features:

• 17 semitone range
• Potentiometer for sweeping up and down the motor speed smoothly
• Pitch-bends control the motor speed
  
• LFO that is mapped to motor speed delta values
• LFO includes user-controllable depth and speed
• Mute switch remembers the last motor speed value pre-mute

It sounds quite okay (dependent on source material).

Tape speed sequencer

A sixteen-step sequencer on a computer controls the speed of a motor in a tape cassette machine.

The controls on the virtual sequencer include speed (how quickly the different steps are read through), length (how many steps are there in the looping sequence) and the actual sequencer itself. The lower a given step is on the sequencer, the lower the speed of the motor is in the tape machine at that point in time.

A special thanks to Edward Kelly for re-igniting my interest in tape control and manipulation.

Video URL: http://www.youtube.com/watch?v=gB6mjDQZ7wc

The music in the cassette player is once again just Drowning Goldfish having a jam. Featuring David Gustafsson on guitar and bass, Brent Easson on drums and myself on bass and guitar.

Tape speed control via pwm

As a follow on from my previous post, i applied the PWM from the Arduino to cassette player. And... success! Well, sort of. I can hear a frequency of around 400Hz when the PWM is too weak to drive the motor. This is annoying, and I am wondering if there is a way to minimise this sound.

This is the same setup as last night, the only difference being that pins 1 and 2 of the ULN 2803 were tied together as well as pins 18 and 17. In the breadboard picture, these new connections are the small, red jumpers placed in line with the relevant pins on the ULN2803 IC (the only IC in the photo).

The reason for this tying together of pins is that i don't have any data for the motor inside of the tape machine. Thus, it might such more juice out of a single set of darlington transistors than they can deliver. Thus, more power can potentially be achieved by chaining multiple sets of the array together. This is a technique taken from page six of the Picaxe Manual (Part Three).

Below you can see a little video (27 seconds) of the thing in action.



For the record, the music on the tape in the video is an untitled number by Drowning Goldfish.