I'm not quite sure what you mean "You only need to match the resistance value with a two wire (variable resistor) setup."
With a 2-wire setup like the Atari 2600 paddles, the encoder is reading the
resistance between the center tab (purple wire) and an outer tab (yellow wire) to determine the position.
- Because it reads the resistance, you couldn't substitute a 5k (5,000 Ohm) pot for the 1M (1,000,000 Ohm) pot in the Atari paddle because it would only cover 0.5% of the range.
With a 3-wire setup, the encoder is reading the
voltage on the center tab. (wiper)
- The pot is acting as a voltage divider with 5v on one outer tab, ground on the other outer tab, and a voltage on the center tab determined by where it makes contact with the resistive element.
- If you turn the pot so the wiper makes contact with the center of the resistive element, you'll get 2.5v (green line) regardless of whether it's a 5k or 100k pot. Half of the voltage drops between 5v and wiper and the other half drops between wiper and ground.
- If you turn the pot so the wiper makes contact 90% of the way from ground to 5v, you'll get 4.5v (blue line) regardless of whether it's a 5k or 100k pot. 10% of the voltage drops between 5v and wiper and the remaining 90% drops between wiper and ground.
http://wiki.arcadecontrols.com/index.php/Analog_Encoders#How_a_potentiometer_provides_the_voltage_for_an_analog_encoder_to_measureWhat does that mean 5k or 100k?
That's the resistance in Ohms measured from tab 1 to tab 3. (outer tabs)
What about my 45 degree rotation?
Different pots have different ranges of rotation.
Pots used in analog joysticks and pedals often have a lower range of rotation.
- This is another excellent reason to start with analog pedals so you don't have to fumble your way through the harder parts of the mechanical and electrical engineering.
You can reduce the range of rotation like Le Chuck did in his SW Micro build, but that's not an easy mod.
- Open the pot case, use conductive ink to bypass part of the resistive element, properly reassemble the pot, and don't turn the pot too far or you'll scrape off the conductive ink.
Scott