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.

1 Answer 1


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.

  • thanks. so input sensibility should say how much voltage I should give them. however, what does input impedance tells me in this particulary case? Dec 8, 2014 at 5:05
  • Input impedance will give you the resistance you should use to determine how much current will flow for a given signal voltage. Dec 8, 2014 at 5:06
  • 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. Dec 8, 2014 at 5:39
  • 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. Dec 8, 2014 at 5:41
  • Two 470 kohm in parallel, right. Thanks for replying. Dec 8, 2014 at 5:44

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