Strange OI potentiometer problem

[ubermeister]

I'm trying to put a POT into our teams custom OI box, but I can't seem to get it to work properly. Here's the setup:

A 100k linear-taper Radio Shack POT is connected between pin 1 (+5) and pin 6 (Y-axis) of port 3. The wiper (center tab of POT) goes to pin 6, and the left tab goes to pin 1.

When hooked up to a program to repeatedly print out the value, it only prints 254.

Now heres the strange part-
I took a multimeter to the pins of the 15-pin connector. The custom POT sweeps between 0 and ~97k ohms between pins 1-6, and a commercial joystick does the same thing. The catch is that the commercial joystick works (value varies between 0 and 254) while the custom POT doesn't (stays at 254).

I have read the OI reference manual, and as far as I can tell have wired it exactly how it specifies.

Am I missing a pin somewhere? Is there something stupid I'm missing or is everybody else as confused as I am?

[DonRotolo]

Pin 1 to Pin 6 is correct, 100k is correct, center wiper and one end are correct...Schematic

Are you sure about the pin numbers? 6 and 9 look similar and are on the same side. Oh, you measured.

Try putting a 47k (fixed) resistor (or similar, anything between 10k and 82k) across those pins and see if that gives you a non-254 reading.

Strange, it's probably something simple. Have someone completely unfamiliar with it check it over, draw a simple schematic showing what you think it is, and have them check it for you. This works more often than you think.

Don

[ubermeister]

Originally Posted by Don Rotolo

Strange, it's probably something simple. Have someone completely unfamiliar with it check it over...

Tried that- I quickly explained what it was supposed to be, and they tested it while I worked on other things, but when I came back they had no better conclusions than me.

I will try the fixed resistor idea, I can probably dig one up somewhere.

And I just thought of this- is it possible that the processor in the OI needs both an X and Y axis to register either correctly?

[Kevin Sevcik]

The OI will work fine with just one pot, as it polls each pin separately. I'd go with Don's suggestion of making certain you're not on the wrong pin. Then I'd check your pins, joints, and pot contacts to make certain you're not shorting two pins together or something. One of those pins shorting to another with throw things off, but be completely undetectable when the connector is off the OI.

[Alan Anderson]

Everything you describe indicates that things should be working properly. So what else aren't you telling us?

The symptom hints that the +5 pin on the joystick port is being overloaded. Has another part been connected to pin 1, and is that other part doing something silly like shorting it to ground?

[Tom Line]

Here is a silly question - do you have all the pins backwards?

My team was wiring up buttons and I had to explain to them that the joystick pinout is actually the pins on the OI, you have to reverse them when you look at the connector on the end of the joystick.

[ubermeister]

Originally Posted by Alan Anderson

The symptom hints that the +5 pin on the joystick port is being overloaded. Has another part been connected to pin 1, and is that other part doing something silly like shorting it to ground?

Thank you for this information!

Like a good scientist, I decided to change all the variables at once. I took a new connector and new wire and put it together, and it worked!

Then I examined the old connector- between two pins, on the bottom, there was a solder bridge between two pins. Not globby and noticable- less than a hair's thickness. I'm assuming this is what was causing the problem. It was an old crappy connector from past years, and I checked it for bridges before using it, but obviously missed this one. The new ones just as old and just as crappy, but it's a different design and the pins are more visible and farther apart.

Again, thanks for the help!