the vectrex controller potentiometer

[vtk]

hi guys i decided to have another look at a faulty vectrex controller which i gave almost gave up on

 

i have a question, hopefully someone can answer (i dont think it is a difficult question, perhaps i think instead i am just easily confused.. )

 

ok so, the 10K pots which the vectrex controller joystick uses...

 

there are 3 legs (lugs) on the pot (the center lug, and the 2 outer lugs)

 

could someone tell me:

 

1. what is the expected value (K Ohms) if you measure resistance between one of the outer lugs of the 10k pot, and the center lug of the 10k pot, when the joystick is centered?

 

2. what is the expected value (K Ohms) if you measure resistance between one of the outer lugs of the 10k pot, and the center lug of the 10k pot, when the joystick is pushed all the way to the left/right?

 

3. regarding the 10K pots, how far (drift) is allowed from the expected values in order for the vectex controller (joystick) to still function adequately (because, there is always some differences between pots, resistance values (tolerance) ... eg. some 10K pots might actually be 9.5K when measured, or 10.5K, etc .. )

 

thanks for any answers

 

[BigO]

1) If it's not connected to other circuitry, it should be about half of the pot value, so around 5k. Should be roughly the same from center to either outer terminal.

2) Center to one side should be very low, possibly zero and center to the other side should be about 10k. Rotate the other way and the values should reverse.

3) The vectrex pot overall value isn't super critical. It's in a voltage divider arrangement. Something in the 10k neighborhood should be effective as long as it's operating properly.

 

You should be able to take your initial measurements from the 9 pin connector without disassembling the controller. You won't be able to crank the pot to it's extremes, but you should see readings somewhat symetrically above and below the 5Kohm center value as you move the joystick through its range.

http://vectrexmuseum.com/share/coder/other/TEXT/SERVICE/5.GIF

[vtk]

hey thanks for the response, ok i think i got it now

 

i was getting confused i think because, the vectrex joystick only uses some of the sweep of the pot (about one third), so i assume all of the '10K' resistance is in that 'one third' area (as opposed to a more common/typical pot where you can turn the knob over a much wider range)

 

one thing to mention, i did try previously your suggestion about using the pins of the controller 9pin connector to measure the resistance of the joystick. i couldnt get any readings at all doing that though (i dont know why). im pretty sure i was using the correct pins (pins 5, 6, and 8 (ground))... maybe i screwed up though (eg. poor connection, or wrong pins etc )

 

cheers

[BigO]

I believe they are just typical pots. The circuitry and/or software would compensate for not seeing the full +5v/-5v range.

 

I usually just straighten out a paperclip or use a piece of wire I have laying around to probe a socket like that.

It could be that your readings were accurate. The controller is defective, after all.

Could be broken wires in the cord, theoretically. Seems unusual that you wouldn't be able to get at least one reading unless somebody got really rough with the cable, though.

[BigO]

. i couldnt get any readings at all doing that though (i dont know why). im pretty sure i was using the correct pins (pins 5, 6, and 8 (ground))... maybe i screwed up though (eg. poor connection, or wrong pins etc )

I missed this earlier. Those are not the right pins. The ground connection isn't involved at all to measure what you're talking about with an ohmmeter and a disconnected controller.

 

I didn't remember all of the details about how those are wired. It's a little more complicated than my memory told me.

If you measure across 7 and 9, you're looking at a network of 3 resistances in series (one variable) in parallel with another identical series network.

[Edit]: it looks like it will be 4.7K + 10K + ~5K (0 to 10K) = nearly 20K, in parallel with the same, looking at something around 10k.

 

Theoretically, it could range from 7350 to 12,350 ohms. But assuming the trim pots are centered and the 4.7K resistors are exact, you would see about 9850 ohms across pins 7 and 9 if everything is in place.

 

If you put one probe on 5 and the other on 7, you should see the resistance vary when you move the joystick in the X direction. The resistance will change the opposite way if you measure between 5 and 9.

 

Same thing should be true for the Y axis if measuring 6 to 7 and 6 to 9.

 

You only need that ground pin connection (pin 8 ) if you're trying measure voltage output from the controller with it powered up by the console. Having the + and - voltages may be a little unusual compared to other consoles. But, those terminals labeled +5v and -5v are not really referenced to ground in the disconnected controller. Ground is the reference for those voltages when the actual voltages are being provided by the console.

[vtk]

hey thanks thats great, i will try some measuring tomorrow the correct way you explained

 

(ps. sorry i should have mentioned previously; when i was trying to measure the pins for resistance values, i was using a different fully working controller i have here, not the faulty controller i am working on)