Hall Effect vs POT based analog joysticks

[u_rebelscum]

I've been doing some research on hall effect and POTs, and I'd like to share what I've found, and see if I have anything wrong.


POT, short for potentiometer, is a variable resistance, mechanical device.

V=I*R, or volts equals current times resistance.  If applied to a POT, V stands for the voltage drop across the POT, I stands for the current that flows through it, and R is the (varying) resistance it has.  So if the resistance goes up, either the voltage drop increases, or the current the flows through drops (or a combo, which is ignored).  Usually (?) the current stays about the same, and the voltage changes (ie: voltage drop increases as resistance increases).  (I know there are times when it's the opposite, but usually the talk is as if the voltage changes.)


Hall Effect is variable voltage, depending on magnets.

V=I*R.  If applied to a hall effect sensor, V is the (varying) voltage drop, I stands for the current, and R stands for the resistance.  So if the voltage drop increases, either the current goes up or the resistance goes up (or a combo, which is ignored).  From what I read, Hall Effect has little effect on the current, so the current usually stays the same and the resistance increases.


Examples:
A 100K POT with a 5 V+ source can have a max voltage drop of 5 V and a max resistance of 100k ohms, so 5 V = I * 100K ohms, or I = 0.05 mA.  

One hall effect sensor I saw, with a 5 V+ source and 1 milliamp current, can have a max 4 V+ drop ouput (from 4.5 to 0.5), so 4 = 0.001 * R, or max R = 4K ohms, which is close to the arcade standard 5K POT.  These are probably interchangable.

To find the POT equivalent hall effect sensor and vice versa, find the stats and use the V=I*R equation.


I don't know the Atari Hall Effect sensor voltage range or the voltage or current it runs at, so I can't say what is the equivalent POT, but if it is like the above hall effect sensor, then a 5k POT could work.


I'm sure I'm making some mistakes; any people with electronic knowledge want to address them?

[u_rebelscum]

Found a link that is said to be the hall effect sensors used by the atari joys.


12 V+ power source
~6.8 to ~5.2 volt output (but not sure if the joystick used the whole range)

[paigeoliver]

I am pretty sure the Microsoft Sidewinder 3D Pro is a hall effect stick, at least it looked like it to me when I tore one open.

[u_rebelscum]

But most controllers use 5V, not 12V like the atari.  (My dreamcast sega-brand controllers are also hall effect.)


And you bring up another point.

If the PC joystick/flightstick/wheel/pedal/etc is connected through USB port, or doesn't use the standard gameport input (such as sidewinders), it doesn't matter on the computer side if it's POT, hall effect, optical disk, 49-way, ect.  The signal is processed on board the controller into the binary-based signal pasted on to the computer, so the computer doesn't know or care if it's a 5k POT, 100k POT, 0.5-4.5 Vo hall effect, or optical, since the controller itself translates it to the binary signal the computer understands.


For us hardware hackers, OTOH, it does matter when we want to hack X stick into Y PC controller.  The output of X stick needs to fall within Y controller's range it can read, and X stick needs to given the needed power (if any).


So now I'd think the arcade atari 12V hall effect sensor would only need a different power source (USB gives 5V), some extra resistors to drop the output down to the range a USB controller could read, and probably some other hacks to get working.