Hardware Reference
In-Depth Information
Controlling the bandwidth with a potentiometer
A potentiometer is like a variable resistor. If you've ever adjusted the volume of a radio or
speaker with a knob, you've probably used a potentiometer. By adjusting the knob, you ad-
just the resistance in the potentiometer, which in turns adjusts the voltage sensed at the out-
put. The potentiometer has three leads: one for voltage (in), one for ground, and the final is
the output.
This knob, connected to BeagleBridge, will throttle the bandwidth available to Tor. With
the dial turned up to max, the bridge will report that all of your bandwidth is available to
route traffic to the Tor network. With the dial at its midpoint, the bridge will report that half
of your bandwidth is available for use. If you notice that the bridge is consuming more
bandwidth than you'd like, as indicated by the LCD, you can turn down the
volume
of your
bridge. The potentiometer and knob for this project are COM-09939 and COM-10001
(SparkFun Electronics).
Your bridge will not immediately attract users; it will take some time. Start with your
bridge set at the max bandwidth; if you discover that it is consuming more bandwidth than
you like, then turn it down. To receive an indication whether the Tor bridge is working, we
will use an LED controlled by a BBB's GPIO, which will flash periodically. This way you
can look over at the panel and tell whether the software is still running. The LED by
SparkFun is COM-10633, and the LED holder is COM-11148.
