Here is a little piece of code to play Happy birthday with Lua from your nspire:

TONE_LOW = "\001"
TONE_HIGH = "\255"

happy_birthday = {262,0.5,262,0.5,294,1,262,1,349,1,330,2,262,0.5,262,0.5,294,1,262,1,392,1,349,2,262,0.5,262,0.5,523,1,440,1,349,1,330,1,294,3,466,1,466,1,440,1,349,1,392,1,349,2}

function freq_key(key)
--return 440 * math.pow(2, (key-49)/12)
return key
end

function keytone(key)
local am = 57600/freq_key(key)
return TONE_HIGH:rep(am) .. TONE_LOW:rep(am)
end

function key_am(key, ammount)
return keytone(key):rep(ammount)
end

function key_time(key, time)
return key_am(key, freq_key(key)*time)
end

function play()
local out = ""

for i=1,#happy_birthday,2 do
out = out..key_time(happy_birthday[i]*5, happy_birthday[i+1]/10)
end
print(out)
end

function on.timer()
    play()
    timer.stop()
end

function on.paint(gc)
    timer.start(1)
end

However, the quality is not so good, because I can't send a byte that contains only 0's, and there is a stop bit at the end of each byte I send (I think). But its ok, you can have fun with it :p

I currently connect a directly a little speaker between the TX and the GND pins of my nspire, but I do not know if this is so safe. Should I add an diode in between?

You need to connect the speaker (or headphone) between the TX and the GND pins on the dock port.

This picture shows how to connect the speaker (Credit goes to TI BANK):



Edit: better picture, thanks Critor!

Well, you might be able to squeeze 2 little cables between the connector strip and the thing that covers it. Tape will also work, but you need to be sure that its on the right spot.

Wow this is awesome. Could you create some kind of a library so we could use a function that lets us put in a note length and hertz amount to play music?

I'll have to try and see If I could write a song with this. thanks for your great work

Does the sound work like on 8x calcs, where you only have a low and a high state? And if so, are you changing the state on a per bit or per byte resolution?

t0xic, the problem is that I don't have full controlling of what I send. I'm using the print() function to send the data to the serial port (so at byte level). 001 is low, and 255 is high. So my wave form isn't perfect at all, but at least you can hear the tones

@thepenguin77, thanks!

t0xic, the problem is that I don't have full controlling of what I send. I'm using the print() function to send the data to the serial port (so at byte level). 001 is low, and 255 is high. So my wave form isn't perfect at all, but at least you can hear the tones

@thepenguin77, thanks!

The quality would improve if you change state on the bit level, by also sending numbers between 1 and 255. So then the highest frequency tone you could play would be represented by 10101010 = 170.