Resistance touch sensors with Darlington array

Hi,
I'd like to build a row of 8 resistance touch sensors.
I am not that familiar with electronics so I started with a tutorial of how touch sensors work: **broken link removed**
This example worked very well and so I wanted to continue to a design with an IC housing 8 darlington circuits. I used the ULN2803A and (with 7 darlington circuits) the ULN2001A.
I connected the Pin1 (Input or Base) with two open cables (my touch sensor) and the other side to Vcc. Pin 18 (Output or Collector) I connected to an LED which was connected to Vcc, too. Pin9 was set to GND. However the whole thing does not work. I am not quite sure why but I think that the connected parts are right but the dimension of the resistors (R1 between my open cables and Vcc and R2 between the LED and Vcc) is not correct. I was trying to read the datasheet of the ICs but was not able to figure out what data is relevant to me. Can someone help?

Thanks

Sas

So what value of resistances did you use?

I have used 220Ohm for R1 and 1.1kOhm for R2.
I've created a circuit diagram.
**broken link removed**
Regards

Sas

The UNL2001 may not have enough gain to light the LEDs.

Have you tried wetting you finger when you touch the electrodes to see if that makes a difference?

Measure the voltage at the ULN2001 output and see if it changes when you touch the electrodes.

Hi,
wetting my fingers will make a difference, yes!! But after a while the LED will go out.
I will fetch a voltmeter tomorrow to check the voltage when I touch it.
Regards

Sas

So it sounds like you need more gain. You could add a small transistor with good gain at low currents, such as a 2N930, with emitter connected to the UNL2001 input.

Alternately you could use a logic level MOSFET as the sole amplifier to drive the LED (no UNL2001 needed) but that would require an added high value resistor (≥10MΩ) from gate to ground to pull-down the gate voltage with no input. You should also add a resistor in series with the gate (≈1MΩ) to help protect the gate against static discharge from your hand.