I'm trying to detect when speaker starts playing audio, my speaker is connected with a 10uF 50v in series with the positive (red) cable coming out of my receiver, and negative to ground.

Speaker (+) ----- || ----- A0 Speaker (-) -------------- GND

I was reading values from around 200 I believe. I had something like input > 210 and it worked(to detect audio). Now at some point and I'm sorry to say I have no clue what changed the reading changed to 100, it looked weird but at that moment I didn't care much and changed my control value to 110.

Now this happened again and I'm reading 36. I'm kinda worried now I'm doing something horribly wrong. Any ideas?

  • 2
    \$\begingroup\$ I dont think the Arduino likes neg voltages .It might latch up or give false readings.Do something about this . \$\endgroup\$ – Autistic Nov 15 '15 at 2:48
  • \$\begingroup\$ Something like what? xD, I'm noob with electronics =/ \$\endgroup\$ – Ceps Nov 15 '15 at 2:50
  • \$\begingroup\$ Maybe a diode ,could be shottky ,you could use two diodes in a half wave voltage doubler. \$\endgroup\$ – Autistic Nov 15 '15 at 2:53
  • \$\begingroup\$ I have a couple of 1N4007, can I use those? \$\endgroup\$ – Ceps Nov 15 '15 at 4:22
  • \$\begingroup\$ Yes you can ,but remember the breakover volts of the diode .It wouldnt detect very quiet sounds which may or maynot be a good thing .If your radio is low power then the answer from jasen will work and i think you should try it .If its a high power thing then limit the input whatever you do . \$\endgroup\$ – Autistic Nov 15 '15 at 4:31

The amount of charge on the capacitor will change the value you see on the ADC.

change the circuit to this.


simulate this circuit – Schematic created using CircuitLab

| improve this answer | |
  • \$\begingroup\$ I'll give it a try asap, I don't have 10k ohm at hand, gonna try to get a couple tomorrow. \$\endgroup\$ – Ceps Nov 15 '15 at 4:37
  • \$\begingroup\$ You can use other values as long as they are the same. Anything larger will do. \$\endgroup\$ – Robert Stiffler Nov 15 '15 at 4:56
  • \$\begingroup\$ what! no 10K resistors? in a survey I did of all the junk electronics that came my way in the 1980s I determiend 10K to be the most common resistor in the world! :) but yeah, as Robert says the values arent very critical as long as they match, and the capacitor can be the 10uF you already have. \$\endgroup\$ – Jasen Nov 15 '15 at 6:33
  • \$\begingroup\$ @Jasen : you obviously haven't worked anywhere 11k was insanely popular ... because nobody bothered to refill the 10k drawer! \$\endgroup\$ – Brian Drummond Nov 15 '15 at 11:39
  • \$\begingroup\$ I have a ton of 220ohm... hahahaha \$\endgroup\$ – Ceps Nov 15 '15 at 16:58

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