Go Down

Topic: Real Speaker (not Piezo) (Read 7 times) previous topic - next topic

Grumpy_Mike

Quote
It sounds like I should be hooking up 120 VAC to the speaker, using an NPN transistor

Noooooooooooooooooooooo!!!!

Keep mains and speakers well apart.

westfw

The speaker has that 1.5W, 8 ohms rating.
P = I*V,  V = I*R, and so P = V2/R   or...
1.5 = V2/8
12 = V2
3.5 = V  (approximately.)

So you don't need more than 3.5V to drive the speaker.  110V would make sparks and let the magic smoke out.
On the other hand, back to P=I*V, or 1.5 = I * 3.5 gives us
I = 1.5/3.5 = 0.43A, more than 10 times the current output of the Arduino.  That's why you need the resistor as well.
With an appropriate limit of 40mA, you'd get P = I^2R or about 0.01W... (additional power dissipated in the resistors.)

You could get some louder by connecting multiple pins to multiple resistors before connecting the speaker, adding their total current capability.

Cheap powered speakers are so common and cheap these days that they're probably a better route.

breic

Quote
The simplest way is to use a transistor, with a lowish collector resistor say 100R. Then couple it into the speaker with a capacitor. That will stop excessive DC current through the coils but still allow AC to get through. The bigger the capacitor the louder it will be. Start off with 1uF.


Excuse the stupid question, but why not only use DC current?  Does that harm the speaker?  So far I have only used DC and it is working fine, just too quiet.  (Thus the circuit is resistor from ground to a transistor controlled by the Arduino pin, to the speaker, to the + end of a 9V battery.)  

breic

Quote
The speaker has that 1.5W, 8 ohms rating.
P = I*V,  V = I*R, and so P = V2/R   or...
1.5 = V2/8
12 = V2
3.5 = V  (approximately.)
So you don't need more than 3.5V to drive the speaker.  110V would make sparks and let the magic smoke out.
On the other hand, back to P=I*V, or 1.5 = I * 3.5 gives us
I = 1.5/3.5 = 0.43A, more than 10 times the current output of the Arduino.  That's why you need the resistor as well.
With an appropriate limit of 40mA, you'd get P = I^2R or about 0.01W... (additional power dissipated in the resistors.)

You could get some louder by connecting multiple pins to multiple resistors before connecting the speaker, adding their total current capability.

Cheap powered speakers are so common and cheap these days that they're probably a better route.


Thanks very much for spelling it out for me!  That's very helpful.  It makes a lot of sense.  Up here in Canada, things tend to be ridiculously overpriced---you don't want to know what I paid for this speaker---but I will see if I can find a powered one.  

Osgeld

dc current keeps it running like an electromagnet, might be the source of your too quiet too, your cone cant really move much if its stuck out at the far end

if you can just get the ac sound wave to the speaker it should be louder, and you do this with a capacitor cause they block dc current after they "fill up" but let ac pass on through

Go Up