Speaker

[AtomSoft]

Hello all i want to make a alarm which is pretty simple for me but i would love to be able to drive a small speaker for the alarm sound instead of a buzzer...

Can anyone point me to how to control a speaker. How to get different tones and stuff from a MCU pin...

Can be AVR, PIC, ARM i dont care really. Its all the same to me heh...

 

[Nigel Goodwin]

You simply set the pin high, wait a time, set it low again, wait a time, repeat.

The time you wait determines the frequency.

You can use timers to do it as well, and there's a website that shows how to play phone ring tones on a PIC using timers, written in C.

 

[MikeMl]

Do not just connect a speaker voice coil from a PIC pin to ground. The DC resistance of the speaker is so low that it will overload the port pin. Put a 100uF or so electrolytic capacitor (6V, properly polarized) in series with the speaker. This breaks the DC path so no DC current is drawn from the PIC port pin.

I would also try to find a 2" speaker with a 30 to 45 Ohm voice coil (they exist), rather than using one with a 4Ohm coil. It will make more sound and load the pin less.

 

[AtomSoft]

I think i get it...Ill give it a try... so a 100uf in series like:

Then pwm a tone in and if i want... like...

BEEP----BEEP----BEEP----BEEP----BEEP


I have to pwm a tone in then delay then tone then delay.. etc.. correct?

 

[3v0]

Is the cap in that schematic reversed ?

 

[MikeMl]

Is the cap in that schematic reversed ?

Yes, the positive end should go to the PIC pin

 

[AtomSoft]

ahh yeah heh.. thanks... actually if they figured out that electricity goes from NEG to POS it would have been correct heh...

New Schem...

Thanks a bunch guys ... im about to go collect some old parts... like old cordless phones and rip some speakers out to test with heh

 

[MikeMl]

No, electrons go from negative to positive; electricity goes from positive to negative.

 

[AtomSoft]

hey you know what i was referring too

 

[Mosaic]

Atom:

Have a look at this...I run 'em directly off a PIC pin with PWM.

https://www.newark.com/jsp/search/productdetail.jsp?id=25R0869&Ntt=25R0869

 

[AtomSoft]

i have those but wouldnt get the loudness i want or if i want to add MP3 capabilities in the future...

I am sure i can build or buy a prebuilt tiny amp if needed. if anything i could always test a mini amp (LM386)

Thanks tho.

 

[futz]

Myke Predko did a little bit about sound from microcontrollers (PICs) in his book Programming and Customizing PICmicro Microcontrollers. Here's a link to the pertinent chapter at Google Books.

 

[AtomSoft]

thanks futz but that kind of confused me heh... i never understood asm like:

movlw 256 - (250-4)

what the heck would be in w ?

 

[MikeMl]

Is it b00001010?

 

[futz]

thanks futz but that kind of confused me heh... i never understood asm like:

movlw 256 - (250-4)

what the heck would be in w ?

Heh You got a calculator between your ears that will do that one easily.

Lucio Di Jasio has some good audio info in the last chapter of his "Programming 16-bit Microcontrollers in C" and the 32-bit book as well. I know you have a copy of the 16-bit book at least.

 

[AtomSoft]

heh why all that work tho? yeah i have to look for it heh

 

[AtomSoft]

I have both heh... didnt even notice these books ... i forgot i bought the "Programming 32-bit Microcontrollers in C Exploring the PIC32" when i first wanted to get into PIC32 but went to arm heh...

 

[Mosaic]

I have a question about the inductive spike from the speaker coil. Given the high dv/dt of the PIC PWM signal, can anyone explain how the inductive spike from the coil is handled without a flywheel diode? Or is it assumed that the built in diode in the PIC handles the spike?

 

[be80be]

A capacitor there DC blocking You don't want a diode across a speaker

 

[Mosaic]

A transient isn't dc....it should pass the cap , not so?