At the workshop last week a ten year old came up with a DAC design I’d never thought of before, which we turned into a really cool and simple melody generator. In the schematic you can see the first three clocks blink the LED’s on and off at different rates (try 4.7u caps and 1M pots). As the amount of light falling on the LDR changes in uniform steps, you can hear the pitch go up and down in a musical way. You could actually tune this to a musical scale if you tweaked the spacing of the LEDs, and put the whole thing in a black box away from ambient light.