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Topic: Multiple ISD1820 sound modules with one speaker (Read 125 times) previous topic - next topic

st3f0

Hello arduino community,
I have some isd1820 sound modules (datasheet) and they're working well so far. Now i want to use several different messages in my project and therefore use multiple sound modules. My question is, whether i can connect multiple isd1820 to one speaker (in parallel) without damaging the modules.

If nobody can tell me, i'll probably just try and report, but i assume this is an easy question for many people.

DVDdoug

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My question is, whether i can connect multiple isd1820 to one speaker (in parallel) without damaging the modules.
No, you can't do that...   There's a rule-of-thumb that you can connect multiple inputs together but you can't connect multiple outputs together.  

To mix audio signals you need a mixer so you'd need a mixer followed by an amplifier that's going to drive the speaker (since the existing amplifiers are going to the mixer instead of to the speaker.   You can make a simple passive mixer with resistors but you still need to follow it with an amplifier.

The problem is that the effective source resistance of the audio amplifier is a lot lower than the speaker it's driving.   The amplifier might have a source resistance of less than 1 Ohm and that means the other amplifier is seeing a 1 Ohm load instead of an 8 Ohm speaker, etc.   Too much current flows and stuff overheats, etc.

It might be easier to think about what would happen if you connect two digital outputs together...  If one is trying to go high and the other is trying to go low, they are fighting each other, you'll get too much current, and you'll get an unknown output.

st3f0

#2
Oct 12, 2017, 09:23 pm Last Edit: Oct 12, 2017, 11:17 pm by st3f0
Thank you very much for clarifying this, DVDdoug! What if i ensure with diodes that current flows only towards the speaker? Would that be an option?

Grumpy_Mike

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What if i ensure with diodes that current flows only towards the speaker?
Then that would screw up the negitave part of your audio waveform and it would not sound good.

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