Hello my friends,

I've been trying to build a function generator using this schematics from this diy :
http://www.instructables.com/id/OscilloPhone-Use-your-Smartphone-as-an-Oscilloscop/ to observe wave forms and learn about them without buying the expensive ones which i can't afford.

I have some questions and the Author is not responding so any help is appreciated,

Info:
In my design:
1- I dropped the bipoler LED cause I don't have it.
2- I don't have the -+8 volt regulators in my town so I dropped them as well and instead I am using two batteries (about 8v each connected in series with one common, +7.5 and -8)
3- Im not using the entire circuit, I've only built the oscilloscope circuit and used only one op amp of the LM324 just to test it at first

My problems:
1- I noticed that the op amp gets slightly worm when measuring a dc voltage from my ATX power supply using the ocilloscope cicuite inputs, is this normal?
2- when connecting the phone out to the phonr jack and using the app , no wave form is shown??
3- what is the minimum voltage for the circuit to operate?
4-I connected the +voltage to pin4 and -ve to pin11 and common to the common of the circuit in the diagram (Is this right configuration???)

Thanks in advance

The original schematics from the link:

 

Also, I forgot to mention that when I connect a regulated +-8 volts from using two Ac-dc transformers such as two smartphones chargers in series with one common and -ve and +ve voltage And connecting it as a power source to the circuit i get noisy waves shown on the phone app even without using the probes on anything
2- when i disconnect the the power supply from the cicuite and keeping the phone connected to it and putting the probes on the ground of my Atx power supply the phone still shows a weird wave form(noisy) even without the op amp bing connected to power source!!!

Any explanations would be appreciated!!