floresta:
20K was not sufficient.
The 20 K pot was either defective or it was not connected properly. The overall resistance of the pot has essentially no effect on whether it will work for this purpose or not.
Don
I agree, I tend to think the 20 K pot may be bad too. A possible scenario to have broken it is to have connect top pin to 5V and the middle pin to GND, while the wiper is very close to the top, literally having a few ohms between 5V and GND. That could exceed the power rating of the pot and burn the internal "wire" open, resulting in a bad pot. Does the above speculation make some sense to someone?