Output devices

Week 9 was output devices week (to be followed by input devices week in week 11!). Neil ran through a slew of hello, world style examples of each, from LED arrays and LCDs to servo and stepper motors (see site).

Most of my work this week was spent doing research for my final project. Since I’ll be relying on an audio output (and a capactive touch input), I stuck to the simple hello, world speaker board, using the hello, world schematic and traces:

Still this took some time to gain a good working understanding – this is the first time we’ve worked with transistors (for the hardware) and required some applications of acoustics (for the software). The circuit is able to emulate an analog signal that is output by the MOSFET-driven speaker from a digital signal using pulse width modulation (here’s a rough idea of what’s happening). The software sets the duty cycle (as I understand it), generating a random (pseudo-random) and unpleasant sound. Here it is: