15 Minutes to a Ribbon Controller 


 If you're truly lazy, you don't even have to solder!   

 

Other MIDI projects/music nonsense here 

YouTube videos of said projects here 

While often used in electronic music, you can oftentimes use a ribbon controller wherever you'd use a potentiometer, with the caveat (at least with this design, which has no sample and hold) that you have to keep pressing down.  I've used this design to control display brightnesses and motor speeds, as well as hooking it up to an ADC & microcontroller to send MIDI CC info.  DISCLAIMER: I know very little about electronics, so try this at your own risk! 

 



The first thing you'll need is some SVHS video tape... that's SVHS, normal VHS tape, in my experience, will not work.  SVHS tapes were used for ADATs, if you remember those.  The ribbon controller in this example is made of my old alt.country band's demo tape, and it's Ampex 489, as pictured:

The nice thing about the SVHS tape is that it's a good size for a ribbon controller as is, and doesn't involve having to source/cut up an anitstatic ankle cuff or bag, although PAIA's design is far, far superior to mine. But, mine's cheap, and one tape can make many, many ribbons, so don't worry about screwing up.

First, take the tape case apart (five screws).  One of the reels should have tape on it... remove it and cut off an appropriate length of tape.


Get your multimeter out and measure the sides of the tape.  One will show resistance... it'll be in the several K ohm range if you measure about 1" of tape; This is your "ribbon"


The "wrong" side of the ribbon will show nothing.



Get whatever material you want to make your ribbon controller out of; I just grabbed a piece of Pergo molding for this example.  Tape one end of the ribbon down...



Then, apply some tape to the other end of the ribbon, pull it taut, and tape it down:
 

Next, find an appropriate power source.  I'm using a breadboard w/integrated 5v regulator because it's convenient, but it can be a 9v battery or whatever.  The total voltage (more or less) of your voltage source is what's going to appear at the "top" of the ribbon, so make sure the voltage range of your power supply is appropriate for what you're using it for, or attenuate the output of the ribbon somehow.  BTW, I'm not responsible if you blow anything up or kill yourself somehow screwing around with this.  Anyhoo, here's my power supply:


Next, attach the ground of your power supply to one end of the ribbon.
 

In the interest of keeping it simple, I'm using alligator clips, but a more permanent method would be to staple or thumbtack through the ribbon and solder or otherwise connect the wire to that.
Now hook up the positive voltage...


That's pretty much it.  The fun part comes in deciding what you want to use as a wiper.  I've used a metal ring suspended above the ribbon on a track of small pullies like an Ondes Martenot, or you can use 1/2 inch metal strapping material, or a guitar string.  Whatever you use has to be conductive, as it is the "wiper" for the variable resistor  you've just made.  To illustrate how it works, here's a couple movies:  One with an o-scope , and one with a DMM.Both show the same thing, which is that the voltage on the wiper depends upon the position of the wiper on the ribbon.  

One thing to consider is that there's a very small current out of this controller as the resistance of the strip is so high (about 1 meg for 12").  That's OK for devices expecting small currents like ADCs, but if you want to control a motor or similar you'll need to step the current up; using one side of an LM324 op amp configured as a voltage follower into a darlington pair transistor will allow you to control small DC motors or similar. 

You may also want to check out my page on sending MIDI with the Ubicom/Parallax SX-28 microcontroller here.  It's a thrilling, spellbinding read.