Help with analog joystick interface

[blcpro]

Does anyone know where to find the specs for the standard game port interface? This is the analog interface for joysticks, etc. I have a project with components that are very much like a joystick, so for development I want to test it out on the game port of my PC. Specifics that I am looking for are:

1) The max current draw from the interface. (Will this be a variable between different manufacturers of game ports?)

2) Details of the pushbutton interface. (is there pullup or pulldown resistors involved? Is there debouncing in the game controller or on the joystick?)

3) The limits of the analog signal. (What are the normal ranges for this signal... I would expect a range of 0 to 5V. Is that correct?)

4) Defining a generic joystick in Windows. Can this be done without any special drivers?


Any help here would be greatly appreciated.

 

[felixc]

Did a search on google...

there it is:

http://www.epanorama.net/documents/joystick/pc_joystick.html

 

[blcpro]

thanks felixc, that link was helpful. I am still wondering about the electrical specs for the interface. What are the allowable max/min currents and voltages?

anyone?

thanks again!

 

[felixc]

Well, this interface works out from 5-volt power supply of the system. How much power do you need?
The buttons are logic inputs with pullups at 5 volts.
The joystick inputs are analog circuitry, running about in the 1.5 to 3.5V range. Do you want to use these inputs?

 

[blcpro]

The "joystick" I have in mind uses 10K pots. Most of the little bits of information I have about the analog inputs seem to agree that the pots be 100K. I'm not sure if my 10K pots will give the full range of values that you'd expect for a joystick. Thats why I'm interested in knowing the detailed specs of the analog inputs. I'm looking for info about the circuitry which the PC uses to read the joystick pot. Will the 10K ohm pot work here?... and what are the standards? ... specs? I like to read and understand the offical documentation if it is available. My problem is that I don't know what the spec is named. Other digital PC interfaces are defined by IEEE or other implementor groups, and have some well-defined documentation for developers to follow... I don't know where to begin with the game port.

Any help here would be greatly appreciated.

 

[felixc]

Okay, this is almost an easy one. If you look at the site that I referred before, you will see that the joystick interface uses a chip called the 558 which is a quad 555. I think that the site gives a link for the datasheet of the LM555. This chip is what generates a pulse as a function of usually two or three resistors.
So you want to connect to a standard joystick port? Well, with a 10K pot, you will only get ten percent of the range of the standard joystick. Nothing else that you can do about it, unless you want to add some active circuitry to your joystick to make it send one tenth of the current that it controls.
If you have control over the interface circuit as well, then you can change the 2.2K resistor to 220 ohms, and increase the capacitance tenfold, to a 0.1uF. This would provide the same range as the regular joystick.

 

[blcpro]

Thanks felixc...

I think I understand the port interface pretty well now. With the game controller interface in windows I can simply connect my 10K "joystick" to the port and re-calibrate it. This gives it the full range of motion I would expect, at the cost of a little accuracy. However, since my project really only needs this interface as a testbench, it has served me well. But now my interest is getting the better of me. Who came up with the game port interface? Its the principal of the thing now...