An audio echo/delay effect “pedal” built around an mbed kit (based on ARM LPC1768).

(Photo: Ivan Sergeev)

Author says: The circuitry of the “pedal” is fairly straightforward: the microphone/input is AC coupled, then amplified around a VDD/2 bias (I'm running on a single supply) across two stages, one of which is adjustable, then passed through a low pass filter at around 10-15KHz to clean out any high frequency in the input, and fed to a microcontroller for some processing. The output of the microcontroller's DAC is smoothed (LPF) out by a cap and fed to a final amplification stage, and then AC coupled to a speaker/output. Although I've labeled this particular project Audio Echo Effect, you can really do whatever you'd like on the mbed/micro for the processing, so I like to think about it as more of a general audio effect platform I can tinker with (though a DSP instead of a micro would probably do better). The mbed and LM358s are the only ICs, the rest of the parts are passives and connectors. Substituting the mbed for a more economical microcontroller with an ADC, DAC (or even building an R2R DAC), and sufficient memory, this project can be built for under $15.
Link: mbed audio effect

Via: EmbeDDS