![]() If (m > 40) /* hack: new note, keep volume */ * enable interrupts on TIMER1 overflow */ * 7-bit precision => 125kHz PWM frequency */ * TIMER0 is used by the Arduino environment for millis() etc. * these magic constants were generated by the following perl script: You'll need tight code to generate audio data from within an interrupt handler, and then you'll need a playroutine to trigger the right notes at the right time. Knowledge of basic digital signal processing (DSP) will come in jolly handy. With multiple voices you can't rely on interrupts to set the frequency your waveforms, you have to stretch them yourself. Of course, once you've got PWM output working the fun is just beginning. I picked 7-bit resolution, which means the output is a 16MHz/128=125kHz square wave with 128 possible duty cycles. Secrets of Arduino PWM has some more information, and here's a detailed reference on how to implement a PWM DAC on an Arduino. So we have to program hardware registers ourself. The bad news is that the PWM frequency is typically 500Hz, which is fine for dimming an LED but way too low for audio. This fakes varying output levels using the Arduino's built-in PWM hardware. In fact, the Arduino has hardware to to this for us. And while we will not get CD-quality audio out of an Arduino, we can get more output values by choosing a duty cycle other than 50%. CDs store 16-bit audio, which means there are 65536 possible values. High-quality audio requires many more values than this. ![]() This is enough to allow us to play two square waves simultaneously: So we now have three possible output values: on, off, and halfway. It's way too high to hear, but the average value is halfway between on and off (50% duty cycle, remember?). Imagine generating a 200kHz tone with tone(). If you diddle your output faster than that, say at 200kHz (well within the capabilities of the Arduino, which is clocked at 16MHz), you don't hear the individual output transitions, but the average value over a longer period. ![]() Humans can hear audio frequencies up to about 20kHz. The idea is that you may only be able to set your output to one of two values, but you can do so really fast. The good news is that there's a trick you can use called pulse width modulation (commonly abbreviated PWM). If you want to play two square wave tones simultaneously, or even to control the volume of a single square wave tone, you need to be able to output more values than just "on" and "off". This is all very well, but most audio waveforms are not square waves. Thus every 5ms the output changes, and you get a square wave at 50% duty cycle, which means the output is on for precisely half the time. Next time it's called it sets the output high. The first time the interrupt is called, it sets the output low, and returns to whatever your program was doing. So tone(PIN,100) will set a timer interrupt to be called every 5ms. 100Hz means the output repeats every 1/100 of a second, or 10ms. ![]() The tone() function, which I expect you've run into by this point, outputs a square wave at a specified frequency. I'm not a master at programming, but I'm not a beginner either.Īrduinos offer only digital output: the output is either on (+5V) or off (0V). If not, could you explain it in the clearest way possible. I understand that it involves phase shifts and adding frequencies of notes, but how do you translate this into code for a piezo buzzer? If you could post some example code that would be greatly appreciated. I mean like the bass and treble clef notes are played simultaneously on the buzzer. Is it possible to play the song on a piezo buzzer so it sounds like it's being played on a piano (or at least close to). Now I'm a piano player (I took AP Music theory), and the problem I'm having is that I'm only able to play one note only the piezo buzzer. Using some creative liberties, I found a nice piano piece of this song (link here). What better way to be creative than to use "Firework" by Katy Perry. We learned about creating songs using the piezo buzzer. Enough about that, right now in the class we're experimenting with the piezo buzzer (it looks like this). ![]() */ #include "pitches.My high school electronics class decided to buy some arduino uno kits, which I must say are extremely cool. * Arduino Christmas Songs Based on a project and code by Romeo Hackster. ![]()
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