Walkman Mellotron?

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I decided to email Mike Walters last night to see if he had any ideas on how to do something similar.  He said funnily enough last night he was talking with friends about making a microcassette version of the melloman

He said he seems to remember something controlling a motor called a Monotron (not the Korg one!) about a decade back that he's not really heard of since!  Using the same principle as discussed - a motor controlled cassette playback keyboard.  It's sounding like that's the most viable option.

So far I like the idea of using a 4-track tape head to group 4 half-octaves, meaning that the motor has a much smaller range of speeds to cover.  The keyboard matrix is the part that has me stumped.

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Another quick question, as it's something I can't find an answer to and someone with more electronics knowledge might know.

I know how a keyboard matrix works (at least roughly, I do) with the groupings of 5 or 6 keys to minimize scans... but in the case of a monophonic one, I don't understand how it knows to stop the last note you played when you press a new key?

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Still thinking about this idea....

I've bought a few microcassette recorders lately and have been pondering how I could do it with those instead.  I'm thinking 5 microcassettes, each one handles 5 keys.

Each has a base note and 2 notes on either side, which would be very subtle changes in motor speed (about 5% per note.)  That way 5x5 = 25 keys/2 octaves.  An Arduino could be set up for a 5x5 scanning matrix and coded so that it uses a PWM to control the motors.  Could be done with walkman style cassette players too I reckon.  I need an arduino to play with methinks!

Would have to be mono as a stereo microcassette would be nigh on impossible to find alone, let alone a bunch of them.

Plus if the quality is a bit poor it'll just add a bit of charm... could ewven experiment with wiring up a microcassette head to some better circuitry!  Ideas ideas...

[Gordonjcp]

Arduino eh?  Y'know, I wonder how well an Arduino would do polyphonic wavetable playback...

If you replace the sine table in the Arduino synth code I posted with a single-cycle sample of a bowed string, you'd maybe get a good effect.

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Arduino eh?  Y'know, I wonder how well an Arduino would do polyphonic wavetable playback...

If you replace the sine table in the Arduino synth code I posted with a single-cycle sample of a bowed string, you'd maybe get a good effect.

So it'd technically be a lo-fi digital sampler in that case?

Sounds very intriguing   I've been working on uni stuff solid for the last 3 weeks and I've got a bit of a break at the minute so I've been looking back over all these old ideas.

You know the Arduino well Gordon - is it possible to drive 5 simple cassette player motors from a single Arduino Uno?  I've been looking at the motor shields but they only support 4 motors, but I'm curious whether they're not suited to something more complicated than what I'm thinking of.

[Gordonjcp]

I guess you could.  There are six PWM channels, and you could easily roll your own motor controller board.  Since all you're doing is switching a motor that runs in one direction then just using a MOSFET as a switch to pulse the motor supply would work.  I *think* you'd need a higher supply voltage than normal for the motor, because you want it to go faster and my gut feeling is that you probably want it to be running at about 50% PWM at "normal" speed so you've got a lot of headroom.  This will let you speed it up quickly - bang the throttle open until it gets up to speed.

Oh, that's the other thing - you could be excessively clever and detect the motor speed by various means (photosensor and a timing mark on the shaft maybe) so that it's a closed-loop system.  That way you can control the motor speed precisely regardless of the load the tape presents.

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Yeah, using PWM at 50% gives it plenty of scope - I worked out the notes are roughly 5% apart but not exactly - sometimes it's 6%, it all varies depending on the note frequency you need to get.  But it only needs to go about 12% faster or slower at maximum, so that shouldn't pose a problem.

I'm thinking it might be best to do this with MIDI input to the Arduino - can be controlled by any 2 octave keyboard then, or even a sequencer.

I'm not quite sure where I'd start with a motor controller, I was hoping to use  something pre-built to save making things more complex

Same for detecting motor speed - might be a bit beyond my scope of ability (well perhaps the whole thing is really but it's a learning project )

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I thought my prayers had been answered before when I found this

http://www.solarbotics.com/products/mcm/

and this

http://www.solarbotics.com/products/mcm2/

which would allow a real polyphonic Mellotron to be constructed much like the Melloman - except for a few problems.  First being that 25 would be required and also that it would require an amplifier circuit (could you have just one with all those heads attached to it, or would it need one per cassette?)

Either way, even with a bulk discount, 25 of them plus international shipping from Canada works out VEEERY expensive and renders it a pointless exercise.  Looking at over £100!

Still, it would be easier to construct since the Melloman proves it can be done.  Plus if you could source a load of those 1 minute endless loop answering machine tapes...