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I know little about electronics in general. I wanted to connect Arduino, and play a tone using tone() through my home speakers.

I've used a 1/8'' audio jack and connect ground to ground and left/right to pin 2. Run it and it was too loud.

Then I read the specification and it says,

Input impedance = 20 kOhm

Input sensibility = 400mV +/- 50mV

Arduino sends 5V so that should be a lot. Did I damage my speaker? They still work.

whitenoisedb
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1 Answers1

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It's probably not damaged, but you shouldn't do it again.

To get the 5V signal down to 400mV you need to create a voltage divider. As such you will need a:

5V / (400mV / 20kohm) − 20kohm = 230kohm

resistor between the pin and the input. 220kohm should be close enough.

Ignacio Vazquez-Abrams
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  • thanks. so input sensibility should say how much voltage I should give them. however, what does input impedance tells me in this particulary case? – whitenoisedb Dec 08 '14 at 05:05
  • Input impedance will give you the resistance you should use to determine how much current will flow for a given signal voltage. – Ignacio Vazquez-Abrams Dec 08 '14 at 05:06
  • I only had a 470 kOhm resistance and I tried with it because it would result in less volume I believed. It worked. However, should I see 4,7V in the resistor between the pin and the input? My multimeter tells 0,01V. – whitenoisedb Dec 08 '14 at 05:39
  • You'll only see full scale if you're actually outputting full scale. Any sort of waveform will result in a value that is lower than maximum. Also 470kohm || 470kohm = 235kohm. – Ignacio Vazquez-Abrams Dec 08 '14 at 05:41
  • Two 470 kohm in parallel, right. Thanks for replying. – whitenoisedb Dec 08 '14 at 05:44
  • Sorry, I mean, I should see 4,7V but I see 0,01V in that 470k resistor. It's strange. 5V / (20k + 470k) = 1x10-5 A ... 1x10-5 A x 470k = 4,7V – whitenoisedb Dec 08 '14 at 05:59
  • I'd probably create my own voltage divider, and not depend on the 20kOhm input impedance. I also think you should AC couple (capacitor is series) it, but I'm not very good at this audio stuff, so I could be wrong. – Gerben Dec 08 '14 at 16:51