3.5 mm mono audio jack pin terminals

Hello,

I am trying to built a vu meter using arduino. I came across to this article ( http://theelectronicbyte.wordpress.com/category/projects/vu-meter/ ) the image shows the Signal & Ground connection as the yellow wire (connected to analog pin) and the black wire. I tried to add an audio o/p in place of the voltage divider of the above project.

I wired the mono jack in that manner ( Only the tip & sleeve, no Ring was present) plugged the mono jack to my speaker's additional headphone o/p jack. Connected the other end of "sleeve" wire to the arduino GND & "tip" wire to the ADC pins. I made all the connections exactly as the first image only altered the POT output with the audio o/p. Uploaded the sketch & all the leds glow & remain bright, no changes.

After that I came across to almost another same project. ( http://learningthearduino.blogspot.be/2012/11/arduino-vu-meter-audio-sound-meter-with.html ) but the signal input is totally reversed. "Tip" pin to 5V & "sleeve" pin to ADC pins. I cannot understand why the "Tip" (signal) pin is connected to 5V & Ground pin to ADC. We have to connect the "Signal" pin to ADC to get readings. The second circuit works fine but can't understand the audio o/p (ADC input) connections.

Shall be grateful for any help. Thank you.

Both circuits are absolutely the wrong way to connect an audio signal to an arduino. An audio signal is AC so if you connect one end to a power rail ( 5V or Gnd ) you will be subjecting the Arduino input pins to damaging voltages. The way to connect up an audio signal is with a capacitor and two resistors. Like the input section of this circuit http://interface.khm.de/index.php/lab/experiments/arduino-realtime-audio-processing/

Thanks Mr. Cook for the link.

Ah.. you used the C word. :)

Okk, got that point. I'll be using only the input interface of the circuit. So, in the input section the two 100K resistor (voltage divider) & the input capacitor is needed ( I shall try with the minimal circuit first ). I have a question.

An audio signal is AC

It is true but AC signal with respect to ground. So If I connect the AC signal to the ADC pin & connect the ground with arduino, what problem will actually arise in the atmega328p? Please explain the consequences in brief. I want to know the pros & cons of using the audio signal with & without the capacitor & the voltage divider in this case.

Grumpy_Mike: Ah.. you used the C word. :)

Got it from the website. XD http://www.thebox.myzen.co.uk/Site/Welcome.html

it is true but AC signal with respect to ground. So If I connect the AC signal to the ADC pin & connect the ground with arduino, what problem will actually arise in the atmega328p? Please explain the consequences in brief. I want to know the pros & cons of using the audio signal with & without the capacitor & the voltage divider in this case.

Any voltage below -0.5 vdc applied to an arduino input pin will cause it's internal negative protection clamping diode to conduct and high current can flow damaging the pin. Anyway any voltage below 0 vdc will return the same 0 digital count as 0 vdc does, so the ADC effectively clamps the whole negative portion of any AC audio voltage waveform applied to analog input pin. A common solution is to wire the audio signal through a series cap wired to the center of a two resistor voltage divider, effectively moving the AC 'zero value' to a 2.5vdc 'zero value'.

Any voltage below -0.5 vdc applied to an arduino input pin will cause it's internal negative protection clamping diode to conduct and high current can flow damaging the pin.

Thanks retrolefty for the answer.

Its really a great place to learn. Thanks to the community. I have learned & am still learning so many things here that I was not even able to understand during my college days. :fearful: shame on me. :~

am still learning so many things here that I was not even able to understand during my college days. smiley-eek-blue shame on me.

No. Well done for trying and not giving up. You might want to read this:- The Theory and Technique of Electronic Music by Miller Puckette You can get it from here:- http://msp.ucsd.edu/techniques.htm

Thanks for the book. After a long long time getting into DSP. That's really a great book. Hope to make something useful with the help of it.