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Topic: ISD1820 to 3,5mm jack (Read 820 times) previous topic - next topic

dc98

Hi, can i connect the ISD1828 to a jack of powered speakers?
And if the answer is yes, how?

DVDdoug

What's an ISD1828?   How about giving us a link?    ....Google doesn't find anything electronic.

You generally won't hurt powered computer speakers with anything  5V or less.    Unless you have high-power speakers and a "loud" tone and the speaker volume turned up, you could blow a speaker.   (The amplifier in most powered computer speakers is not powerful enough to fry the drivers.)

dc98

http://www.e-voron.dp.ua/files/pdf/Modules/ISD1820_Module_.pdf
Thanks

DVDdoug

I found the datasheet for the chip here.   Look at the bottom of page 7.  The speaker output is "special".   It's a bridged "push-pull" output (with no ground).  You need to block the DC from this signal, and your powered speakers should be connected to ground.* 


The best solution is to put a capacitor (1uF or greater**) in series with the SP+ output and the powered-speaker input with the + side of the capacitor toward the sound module.   Then connect the speaker's ground to the sound module's ground.  

Leave the SP- pin unconnected.
  Connect the left & right speaker wires together so you get sound from both speakers.



* It can sometimes "work" if you connect the speaker ground to SP- as long as there is no common  ground between the two circuits.    But, that's a little "dangerous" because there is sometimes a "backdoor" ground through the power supply, or one set of powered speakers may be connected to house-ground and another set of speakers may not, etc.


**  The bridged output has a DC bias, and the capacitor will block the DC while allowing the AC sound signal through.    If the capacitor is too small, low frequencies (bass) will also be blocked.   Since we don't know the exact input impedance of your powered speakers I'm only guessing at 1uF, but that should be fine.   There is probably already a capacitor at the input of the powered speaker's input amplifier, but it's good-practice to make sure your circuit is not putting-out DC along with the audio signal.

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