9.5V circuit (5V output) to arduino

Ehi there,

I created a circuit working on 9,5V (19V power supply) with 0-5V output. I want to connect it to arduino analog input. My problem is that when I connect my circuit's GND and output to arduino, both my system and arduino input value are stuck.

My first attempt was to add a 10K resistor btw my circuit's output and arduino analog input; a pull up 100K resistor btw arduino 5V and analog input; a pull down 0,1uF capacitor btw arduino analog input and GND (connected to my system's GND), the result is exactly the same. My circuit even gives no data.
After trying with different resistors for the pull up and pull down set, I tried to convert my analog output to digital and send it to arduino digital input: I used a buffer CD4050, I charge it with 5V (first from arduino 5V, then from my circuit) then i sent my output to arduino, and the result... still the same.

Does anybody got this kind of problem? I really have no idea what it could be... I m using maxuino and firmata to communicate with arduino. My circuit is build with: 1 antenna system giving data by touching; a potentiometer to regular the antenna's output; an amplifier which gives the final output data from 0 to 5V (or less).

Does anybody know if I have to change some setup inside Firmata to change the internal pull up value or it is enough to work with external resistors? All I have to do is sending analog or digital signal to arduino, but it seems so hard, if I only connect two systems through GND or analog input, my circuit stuck and of course arduino is giving no data...

hope to have some suggestions from you soon...
thanks in advance

To avoid confusion some sort of circuit diagram (if only hand-sketched) would be really useful...