Stompbox Rapid Prototyping

From CCRMA Wiki
Revision as of 05:24, 18 May 2011 by Eberdahl (Talk | contribs)

Jump to: navigation, search

Lab 3: Rapid Prototyping
Designed by Edgar Berdahl (and Esteban Maestre?)

Making an enclosure is time-intensive, so in the context of the workshop, we recommend exploring ideas and designs first in a rapid prototyping context.

Cables For 1/4" Connections

In many applications, it may be desirable to connect the audio converters of the Beagle Board to generic 1/4" audio cables. For example, a generic prior-art guitar stompbox would incorporate these elements, and it could be convenient for other applications as well. Since no appropriate, mass-produced cables are available, we show you how to make your own using elements from your kit.

The following image shows a female panel-mount stereo 1/4" audio jack connected to an 1/8" male, stereo audio plug that can connect directly to the Beagle Board. As shown in the figure, heat shrink covers the soldered connections to help prevent any short circuits. StompboxCompletedCable.jpg

We recommend making one cable of this length and one slightly longer to facilitate connection to the enclosure.

You can use a heat gun to shrink the tubing around the connections. The trick is to put the heat shrink over the wires before you make the soldering connections; however, you have to be careful not to heat the heat shrink tubing with the soldering iron because then you will not be able to move it over the connection later. You can read instructions on how to use heat shrink tubing for more information.

Here you can see what the connections could look like at the 1/8" male end after soldering but before applying heat with the heat gun: StompboxBeforeHeatShrink.jpg

Try Incorporating Other Sensors

  • So far you have been using a potentiometer for controlling effect parameters:


  • but you could also use a force-sensitive resistor (FSR):


  • or a bend sensor

Bend sensor.png

  • or a photoresistor


  • or an optical reflective sensor

Optical.png The reflective optical sensor consists of an infrared LED and a phototransistor that passes an amount of current proportional to the reflected light received. We use two kinds at CCRMA, the Fairchild QRB1114 has the letter "E" (Emitter) to label the LED, and the label "S" (Sensor) for the phototransistor. The Optek OPB704 uses the symbols for an LED and a transistor to label the two sides. One leg of the sensor is connected to +5V, which supplies current, and the voltage drop across the 10k resistor that we measure is proportional to the amount of current.

Experimentation With Fancier Audio Effects


Important Note

Some small amount of the text and images here was taken from prior laboratory exercises for the course Music 250A. We regret that we do not know who contributed these elements, but these people are likely to include Wendy Ju, Bill Verplank, Michael Gurevich, and possibly more.

Stompbox 2011