Making a digital delay from a simple microcontroller

If you’d like to start experimenting in DSP, or just want to build a guitar pedal, here’s the project for you. It’s an audio echo using just a microcontroller from the fruitful workshop of [Vinod].

For his circuit, [Vinod] fed the output of a small electret microphone into a small amplifier, and then into the ADC of an ATMega32. Inside the microcontroller, [Vinod] set up a circular array which writes the voltage from the microphone and sends it out to a speaker. Because the array is circular (i.e. it loops around when it gets to the end), [Vinod] has a digital version of a loop of magnetic tape, perfect for recording sounds and playing back echos.

Because [Vinod] is using an ATMega32, he only has a limited amount of RAM to record audio samples. The delay time could be lengthened with a more capable microcontroller, or even the addition of a large RAM chip. With his setup, [Vinod] can do some really interesting experiments with audio and DSP, so we wouldn’t be surprised if an enterprising musician used this project as the basis for a digital delay stomp box.

You can check out [Vinod]‘s demo of his echo machine after the break.

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Tape delay made from recycled cassette decks

Professional tape delay units are great fun, but often expensive. You’d think that with so many derelict cassette decks filling the world’s dumpsters someone must have figured out a way to make a cheap tape delay… not only in the interest of saving money (sometimes quality is worth paying for) but also in the interest of re-using otherwise wasted resources.

Forosdeelectronica forum user [Dano] has made just such a device from used cassette decks and miscellaneous parts (translated). First he investigated the operation of the playback, erase, and record mechanisms and broke out the tape heads. The playback head is on a plastic rail so that the delay time can be changed, while the record head is fixed. [Dano] encountered some difficulties in ensuring good quality for the recording and erasure, which is an important consideration when working with magnetic tape.

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Guitar echo pedal built with mbed

[Vsergeev] built an echo pedal for a guitar or with other audio manipulation applications. He used an mbed microcontroller for the project. You may remember Hackaday writer [Phil] labeling the mbed an ‘Arduino on steroids’, and it certainly handles this audio processing quite well. We’ve included a clip of the echo effect after the break. During the design process, [Vsergeev] used LTspice to simulate the analog circuitry and make things right before committing to the physical circuits.

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