I suspect this is basic, but I can't figure it out....
I have a potentiometer that I only have access to the variable end and one of the fixed ends [1]. I want to use it to feed an ADC. The potentiomenter is supposed to be 1M, but in reality it measures between 815 and 840K (and between 50 and 80Ω on the other end). I tried using a voltage divider. With 5V and an R1=390K resistor, the voltage that goes into the ADC ranges approximately between 0V and 2.5V [2]. If I keep making R1 smaller, and smaller, to get closer to 5V, there's a point where it gets stuck at 4.60V (unless I use really small resistors, which get really hot), and it never reaches 0V on the other end. Also, with small resistors, the voltage doesn't change when I turn the pot, until it suddenly changes from one extreme to the other...
There must be an easier solution to work this out... Help, anyone? Thanks!
[1] It's the Atari Paddle. Only the variable end and one of the fixed ends are wired into the DB-9 connector. Ripping the Paddle to gain access to the other fixed end is out of the question because I want this to work with any Atari Paddle, not just with an altered one.
[2] The ADC I'm using is the ADC0804. I haven't look at it much yet, because I'm working on fixing this other issue first. Is it possible that the ADC0804 has a way of telling it that the maximum voltage is 2.5V, and therefore 2.5V should be 0xFF?? Is that the function of the Vref pin? If that's the case, that would make everything simpler, but I'd still like to know how to do the other thing.
I have a potentiometer that I only have access to the variable end and one of the fixed ends [1]. I want to use it to feed an ADC. The potentiomenter is supposed to be 1M, but in reality it measures between 815 and 840K (and between 50 and 80Ω on the other end). I tried using a voltage divider. With 5V and an R1=390K resistor, the voltage that goes into the ADC ranges approximately between 0V and 2.5V [2]. If I keep making R1 smaller, and smaller, to get closer to 5V, there's a point where it gets stuck at 4.60V (unless I use really small resistors, which get really hot), and it never reaches 0V on the other end. Also, with small resistors, the voltage doesn't change when I turn the pot, until it suddenly changes from one extreme to the other...
There must be an easier solution to work this out... Help, anyone? Thanks!
[1] It's the Atari Paddle. Only the variable end and one of the fixed ends are wired into the DB-9 connector. Ripping the Paddle to gain access to the other fixed end is out of the question because I want this to work with any Atari Paddle, not just with an altered one.
[2] The ADC I'm using is the ADC0804. I haven't look at it much yet, because I'm working on fixing this other issue first. Is it possible that the ADC0804 has a way of telling it that the maximum voltage is 2.5V, and therefore 2.5V should be 0xFF?? Is that the function of the Vref pin? If that's the case, that would make everything simpler, but I'd still like to know how to do the other thing.