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I use this circuit to convert audio signal to infrared signal and control my DSLR camera. It works fine on my laptop jack, but when I plug it to my smartphone jack, it shows some malfunctions in touchscreen (random taps without my Interference). How should I prevent this? (I use a DC adapter(+ ground wire) as power source, but it will be replaced by battery later)

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I've run into similar problems with capacitive touchscreens due to EMI from the DC adapter. If the problem goes away when you remove your power source, this is likely what you're running in to. To be certain, rig up some batteries to power your circuit instead.

If the problem disappears when you're battery powered, then the switching action in your DC adapter is causing your issues. In that case, you'll need to look around for an new adapter. In my case, simply switching to an adapter that was earth ground shielded solved our problems. These adapters at the very least utilize a three-prong connector (NEMA 5-15P in the US).

Good luck!

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A smartphone typically has a TRRS jack, four conductors. Using a TRS jack with three conductors like you are is causing a conductor to short. That conductor carries the mic input and button press signals. You are triggering the pause play, answer call hang up actions at the very least. Use a four conductor plug.

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  • \$\begingroup\$ Thanks you for your fast response, but it works fine with my three conductor earphone and I can hear the same audio signal I want to convert to infrared without any problem by that earphone \$\endgroup\$ – Zanyar Apr 30 '15 at 19:21
  • \$\begingroup\$ An earphone isn't injecting power. And maybe your smartphone output signal strength is too low to trigger the transistors. It happens all the time. \$\endgroup\$ – Passerby Apr 30 '15 at 19:31

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