echo effect circuit

Posted on Feb 7, 2014

A video of my friend James playing his electric guitar, patched through the audio echo effect system, and then to his amp. I didnG ‚¬ t make any effort to prove that this isnG ‚¬ t a conspiracy, so youG ‚¬ ll have to take my word that the echo effect is actually happening on the breadboard and not some hidden pedal or options on h

echo effect circuit
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is amp. While IG ‚¬ m at it, I apologize for the camera phone video quality. This project is an audio echo/delay effect G ‚¬ pedalG ‚¬ ½ of a sort, though I did most of the testing with a regular electret microphone and ear buds or external speakers. The circuitry of the G ‚¬ pedalG ‚¬ ½ is fairly straight forward: the microphone/input is AC coupled, then amplified around a VDD/2 bias (IG ‚¬ 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. I used an mbed, which is a LPC1768 hardware platform plus all of that arduino pseudo-coding, because theyG ‚¬ re pretty neat and super quick to develop with, but any micro with an ADC and DAC will do. The output of the microcontrollerG ‚¬ 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 IG ‚¬ ve labeled this particular project Audio Echo Effect, you can really do whatever youG ‚¬ 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...

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