We hear echo effects in most of music records. It is common effect that evolved from analog in to digital methods. Earlier this was done using magnetic tape loop where sound effect was recorded once and played back with some delay multiple times that gave desired effect. Now it is all digital and echo can be implemented using simple DSP method. Vinod constructed simple echo circuit around atmega32 microcontroller that illustrates this effect.
He achieved this effect by using circular buffer where samples from ADC are written in one place and played back from another point what leads to delay. The biggest problem here is that Atmega32 has very limited amount of RAM (2KB) if you want to achieve better sound quality use bigger microcontroller with more RAM. As always vinod’s C code is short and easy.