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I am using Arduino UNO and did a project to sync LED to audio. I am not sure how to read a value from a speaker.

I connected a LED to Pin 9 (PWN) with 220ohms and ground. I connected A0 pin to a speaker pin and ground pin the other pin on speaker. I used the Smoothing example of arduino input and modified the code a bit to output to LED. The speaker I used was with an old Phillips Music System and had only two pins. I played the music and led synced perfectly and everything worked fine. The project was a success.

Today I wanted to try to connect to a home theater (5.1 Sony HT-IV300 Model). This speakers also have same 2 pins. So I did everything same. A0 to Speaker pin 1 and Ground to Speaker pin 2. But suddenly the Music System went to power protect mode and A0 is stuck at ~1000 (975 - 977). I connected the arduino again with the Phillips Music System (Same setup) but A0 is always gives ~1000 value. Connecting to A1 and changing the code works perfectly fine!

Where did I go wrong? I cannot understand, what happened to A0 pin? What is the correct way to read the speaker values?

Thank You. Abhi

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  • \$\begingroup\$ You really shouldn't connect an ADC input to a speaker but rather to the line or head phone output. \$\endgroup\$
    – Dan D.
    Mar 11 '15 at 8:48
  • \$\begingroup\$ You've probably destroyed the A0 pin by connecting it to the high powered speaker. \$\endgroup\$
    – pjc50
    Mar 11 '15 at 9:14
  • \$\begingroup\$ How could it be destroyed? Voltage is merely 0.15 volts (according to multimeter) \$\endgroup\$ Mar 11 '15 at 9:28
  • \$\begingroup\$ @DanD. Home Theater dose not have any direct audio out. Only speaker out and audio in (Some HDMIs) \$\endgroup\$ Mar 11 '15 at 9:29
  • \$\begingroup\$ Used the A0 as output and connected a LED (with 220ohms).DigitalWrite dose work but it only give half brightness when HIGH and dose not go to zero brightness at LOW. Hope this helps. \$\endgroup\$ Mar 11 '15 at 10:01
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How could it be destroyed? Voltage is merely 0.15 volts (according to multimeter)

If it were 0.15 volts and the speaker was an 8 ohm speaker, the power output to the speaker would be 0.15*0.15/8 = 0.028 watts. Does this seem likely or does it seem more likely that the multimeter isn't giving you the full picture?

If in fact you were driving 1 watt into the speaker, the RMS voltage would be 2.828 volts with a peak voltage of that is significantly higher maybe 4 to 10 volts for music type signals.

This level of voltage and the level of current that the amplifier output is capable of providing will certainly damage an ADC input on a chip. Next time use a 10k resistor in series and maybe also a coupling capacitor.

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  • \$\begingroup\$ Okay dont know so much about electrical terms. Anyway I reread the Multimeter values Speaker with wire - 6.5 ohms - 0.2 mv Only Speaker (No wires Connected) - 4.7 ohms - No voltage (ofc :P) Only wires - 150 mv \$\endgroup\$ Mar 11 '15 at 9:49
  • \$\begingroup\$ Used the A0 as output and connected a LED (with 220ohms).DigitalWrite dose work but it only give half brightness when HIGH and dose not go to zero brightness at LOW. Hope this helps. \$\endgroup\$ Mar 11 '15 at 10:01
  • \$\begingroup\$ My answer still stands. That pin is broken. \$\endgroup\$
    – Andy aka
    Mar 11 '15 at 10:25
  • \$\begingroup\$ I agree... it is broken no doubt (Can use for spare output though if needed). But still how can I connect another pin to the speakers to read the audio signal and sync a led, properly? A circuit would be nice :) \$\endgroup\$ Mar 11 '15 at 10:34
  • \$\begingroup\$ Last paragraph of my answer hints at a series resistor but without fully knowing what you want to do I can't really answer. \$\endgroup\$
    – Andy aka
    Mar 11 '15 at 11:50

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