building sensors for use with the pc1600 mod
warning!!!
while this mod is pretty safe if done correctly, it could potentially ruin your box,
particularly if you start sticking things into the jacks indiscriminately. don't do that.
as always, do this hack at your own risk. i don't think it will blow up your pc1600,
but it could, so be prepared!
the general idea
we can use two types of sensors with the new pc1600 controller inputs: voltage dividers, like potentiometers and sliders, and variable resistors, like photocells, bend sensors, pressure sensors, etc. you must wire the sensors up correctly!!! if you don't they won't work, but more importantly, they could damage your pc1600. so make sure you know what you're doing before you start plugging things in.
the specific idea
what you need
- some large potentiometers. any value is fine.
- some small (pc mount) potentiometers. largish values are good.
- some variable resistors, like photoscells or bend sensors. you can get some of these at radioshack. all electronics corp is a great source of weird sensors. but they have to be variable resistors of one sort or another. for instance, an accelerometer that puts out pulses won't work.
what to do
we'll start off with a potentiometer, which is very easy to hook up. you can get pots at radioshack or any electronics place. the pot should have three pins: a voltage input pin, a voltage output pin and a ground pin. guess how we're going to hook it up?!?
- get a 1/4" stereo plug. it has three pins, tip, ring and sleeve. you want to hook the tip pin to the input pin on the pot. then hook the ring pin to the output pin on the pot and the sleeve pin to the ground pin on the pot. that's it!
- plug the pot into one of the 1/4" jacks. turn on your pc1600 and move the slider corresponding to the jack you're using all the way up. now turn the pot. you should see the value on the pc1600 changing!
- if you move the slider all the way to the top on the pc1600 then the pot should give you the full 0-127 midi range. if you move the slider to the middle (64) then the pot will give you 0-64. so you can use the sliders to scale the range of the pot. if you move the slider to the bottom then the pot will have no effect. but neither will the slider, so that's not really very useful!
- you'll probably notice that other sliders seem to be changing their values occasionally as you move the pot. that's why you need some dummy plugs, since leaving the jacks open makes them susceptible to interference from the other sliders.
- to make a dummy plug just connect the tip and ring pins on a plug to each other. you can leave the ground unconnected. it's a little hard to see in the image above, but there's a little wire connecting the tip pin and the ring pin. you don't need any external wires or anything, just the one short-circuit. what you're doing is reestablishing the original connection between the slider and the pc1600.
pots are fine, but other sensors are finer. there's a problem though, in that most of them are variable resistors and not voltage dividers. but we can easily convert them.
- get a variable resistor, like a photocell or a pressure sensor. it will have two wires, which are like two adjacent legs on a potentiometer.
- now get a small potentiometer. you'll want something like a pc mount pot for this, as the regular pots are too big. radioshack sells little packs of these. usually instead of a long handle they'll have a little dial that you turn to change the resistance. the pot will have three legs, but we're only going to use two of them.
- connect the variable resistor and the pot as shown. then proceed as if you were using a potentiometer, as above.
- you'll want to select a fairly large resistance value for the pot in this case, as you'll be using it to adjust the range of the variable resistor. a larger range will give you more room to make corrections.
- i have been taping the pots to the side of the 1/4" plug. that keeps it out of the way, which is good since usually you just set it and forget it.
- note that hooking up a variable resistor in this way will cause its resistance curve to be non-linear. that's because in a real voltage divider, the resistance on one side goes down as the resistance on the other goes up. in this case, one resistance stays the same as the other changes. so the change in the ratio between them is not linear, which means that the voltage output will not be linear either. you will notice that the sensor is more sensitive at one end of its range than the other. it's not usually a problem, but if you're having trouble with a controller, it's something to think about.
alright! that's it. here are some pictures of a few sensors i've built. there's tons of info on building sensors out on the web. have fun!
credits:
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.