We see many Arduino tasks that function audio output, however they have an inclination to require a considerable quantity of extra {hardware}. Audio recordsdata take up a whole lot of space for storing, in order that they require one thing like an SD card adapter. Audio alerts are analog, in order that they require a DAC (digital-to-analog converter) to get good high quality. After which, to make the audio sign highly effective sufficient for a speaker, these often want amplifiers. However Scott W Harden discovered a option to make an Arduino UNO Rev3 speak with none extra {hardware} past the speaker.

On this case, the Arduino can converse any quantity, from zero to 9, out loud by means of the speaker. That is doable as a result of these are very quick phrases (most solely a single syllable) which might be recognizable when the standard could be very low. This audio high quality wouldn’t be appropriate for music and even normal language, however it’s sufficient for a sequence of numbers. By lowering the audio high quality as a lot as doable and making the clips quick, Harden was capable of create audio recordsdata sufficiently small to slot in the 32KB flash reminiscence of the UNO‘s ATmega328 microcontroller with room to spare for the sketch.

Harden began with regular MP3 recordings of the spoken numbers. He then carried out a 100Hz to 2.5kHz band-pass on the clips, resampled them to 5kHz, after which transformed the waveforms to eight-bit unsigned values to retailer in program reminiscence. The Arduino can then play these waveforms by means of PWM (pulse-width modulation). A low-pass filter, comprised of a capacitor and resistor, helps easy the PWM output into one thing nearer to a real analog waveform. An non-obligatory LM386 chip can amplify the output, however Harden discovered that he was capable of drive a speaker immediately with out that.