the general idea

the existing sliders work as voltage dividers. they have three pins -- one is tied to +5v, one to ground and the third is the output, which puts out a voltage that varies from 0v-5v as the slider is moved. this voltage is read by the pc1600 and is converted into a midi value. in this hack we take the output from the slider and instead of feeding it to the pc1600, we use it as the input (like the 5v pin on the original voltage divider) to another voltage divider, the output of which is then read by the pc1600. this second voltage divider can be anything you want it to be, as long as it can be configured correctly. i wired mine up with 1/4" stereo jacks so that i can plug in different sensors depending on what sort of control i need. since we're using them as voltage dividers, the resistance range of the sensors doesn't really matter, which makes for a pretty flexible setup.

typical potentiometers are easy to use as voltage dividers, since they have three pins. however, many of the other interesting sensors (photocells, bend sensors, pressure sensors, etc.) are really simple variable resistors, so they only have two pins. you can still use them, you just have to do a little extra work. see the section on building sensors below.

there's one caveat: while the original sliders will still work normally, you will need to build 16 "dummy" 1/4" plugs to use when you're not using the external sensors. this is because when there is no plug in one of the jacks there is no connection to the pc1600, meaning it can't read the position of the slider. the dummy plugs are also needed if you are only using controllers on some of the sliders -- any jack that is left open/unconnected will behave unpredictably, meaning you'll get midi spurious signals from the pc1600. you could get tricky and use some sort of switching jack, but i didn't feel like going that way. you could also just have two sets of ribbon cable, one original, one hacked.

finally: always turn the pc1600 off before inserting or removing a sensor plug! and watch out for static electricity -- always ground/discharge yourself before handling the box. if you are really ambitious you might want to hook up some buffers between the jacks and the pc1600, as it's pretty easy to blow out CMOS chips with a mod like this. caveat hacker.

the specific idea

what you need

• some little screw drivers
• a soldering iron and supplies
• a multimeter or continuity checker
• some ribbon cable. okay, you don't absolutely need ribbon cable, but this won't be much fun if you try to do it with lots of individual wires.
• heat shrink tubing (preferred) or electrical tape (easy)
• a medium size metal project box with 16 holes in it...
• 16 1/4" stereo (three connector) jacks (female)
• a bunch of 1/4" stereo plugs, including some for making dummy plugs
• some sensors, or at least one potentiometer to test things out.

what to do

essentially what you're going to do is reroute the ribbon cables that connect the two circuit boards in the pc1600 so that some of the wires are hooked up to the external 1/4" jacks. you don't want to cut all of the wires, and the ones that you do cut must be hooked up correctly, or you will most likely fry part of your pc1600. so pay attention! it looks like there's a lot to do, but it's really very simple, so you might want to just read this a few times until you can visualize what you'll be doing. once you understand it it should be pretty easy going...

diagram 1

• start by taking the bottom off of the pc1600 and turning it over so that you're looking at the ribbon cables. notice that the red strips on the ribbon cables point to the front of the pc1600. remember that!
• remove the 2 ribbon cables connecting the circuit boards in the pc1600. they're grey with a red stripe and a red header (red plastic thing).
• cut the back ribbon cable (labeled HDR201 on my pc1600) in half.
• starting at the side _opposite_ the red wire, cut the following wires on the front ribbon cable (HDR202) at the halfway point: 1, 2, 4, 5. that's right, leave wire 3 connected and all the other wires connected!
• diagram 1 shows what each grey cable should look like after you're done cutting wires.
• cut 2 strips of new ribbon cable, about 12 inches each. you'll need 18 wires in each strip.
• strip about 1/4" off of both ends of all the wires on the new and the grey ribbon cables.

diagram 2
from left to right, top to bottom:
severed header 1, new ribbon cable 1,
partially severed header/ribbon cable,
new ribbon cable 2, severed header 2.

• look at diagram 2. identify the five parts: severed header 1, new ribbon cable 1, partially severed header/ribbon cable, new ribbon cable 2, severed header 2.
• connect (solder) new ribbon cable 1 to severed header 1 and the four cut wires on the partially severed header/ribbon cable. then connect new ribbon cable 2 to severed header 2 and the four cut wires on the other side of the partially severed header/ribbon cable.
• hopefully you're using rainbow colored ribbon cable. make sure that the colors match up on each header. that is, make sure that on the severed headers, the same color wire is attached to each of the red wires on the severed header.
• stare at the diagram until you get this, because if you do it wrong it will be a real pain to fix and you could seriously damage your pc1600...
• either put heat shrink tubing or electrical tape around all the solder joints -- they're very close together and you don't want them touching!

diagram 3

• diagram 3 shows the wires connected to the headers on the circuit board that the sliders are soldered to. the numbers refer to the 16 sliders. the wire labeled "1" carries the voltage output from slider number 1's voltage divider. if you look at the circuit board, you should be able to trace the connection from the header to one of the pins on the 1st slider. if you can't then that's bad! maybe your board is different from mine. but i think you'll see what i mean.
• you job is to take each numbered wire and to connect it to the pin of the 1/4" jack that connects to the tip of a stereo 1/4" plug. see diagram 4. ("T" "R" and "S" are tip, ring, sleeve.)
• you'll have have to figure out the pins and whatnot on the jacks and plugs for yourself, as there's a good chance yours are different from mine. use the multimeter to figure out which pin connects to which part of the plug/jack.
• i'm using the following scheme: tip = voltage in from slider; ring = voltage out to pc1600; sleeve = ground connection.

diagram 3

• start hooking things up. start with the header that connects to the lower circuit board, the one with the sliders on it. use diagram 3 to connect each of the numbered wires to the pin of a 1/4" jack that touches the tip of a 1/4" plug. there are 16 of them, 14 on the first header and 2 on the second header. note that the wires are out of order -- the first wire is really slider number five! so you're going to have to do a little wire crossing. give yourself a lot of slack.
• when you've finished you will have connected the output pins of the 16 sliders to the tip pins of the 16 1/4" jacks. hopefully.
• now you're going to do the other side. you'll be connecting the ring pin of the 16 jacks to the remaining wires on the headers, which in turn connect to the pc1600.
• if you're using rainbow ribbon cable and you set things up right then you can just match the colors on the two pieces of ribbon cable. otherwise be careful that the wires are hooked up in the right order so that you can trace all the way from a pin on the slider side of the header, up to tip pin on the jack, jump across to the ring pin on the jack, then down the wire to the corresponding pin on the pc1600 side of the header. the idea is to put the wires back together the way they were, but with a jack in between! okay.
• you should have 4 unconnected wires still (2 on each piece of cable). these are the ground wires.
• this part is a lot simpler. just connect all of the ground pins on the jacks together. you might want to strip a long piece of solid wire and sneak it around inside your project box so that it connects to all of the jacks. then just solder the two ground wires to your long solid wire. the idea is that you want to have all of the ground pins connected to each other and to the two ground wires.
• reconnect the headers to the circuit boards. make sure you orient them right. look at the photos if you're unsure. remember that the red wires face the front of the pc1600. it will be a bit awkward to get them back into place, but it should be doable!

that's just about all there is to do on the pc1600 end. hopefully now you have a bunch of jacks mounted in a metal box, and two strips of ribbon cable coming out of the box and going into the pc1600.

here are some pictures of the completed mod. if something above has confused you, maybe one of these pictures will help...

okay, now it's time to make some sensors.

hack by: douglas irving repetto
using stuff owned by: the computer music center at columbia university.
peavey's page for the pc1600
things to make you happy.