View Full Version : Variable Resistor Problem
01-24-2002, 06:38 PM
I am having a problem with the analog inputs.
I have a normal 100k Variable resistor +5V and Ground are on pins 3&4, and the middle wire off the variable resistor onto pin 2.
The variable resistor works fine, I have tested it with a meter on a seperate +5V and ground. When it is plugged into the RC analog in, the variable resistor stops working. The Voltage that comes off the center connection is always 5V. Nothing changes when you dial it up or down. Everything is hooked up according to the diagram, I have double checked it and had other people check it. When I connected the +5v and ground to an independant source, and just the center wire to the input pin 2, it does the same thing. I am not trying to pull it up into the dashboard viewer or anything, just been checking the voltage with a meter.
Any help would be appreciated.
--Gascogne, Chief Armaments Officer, MPS Nirvana
01-24-2002, 08:53 PM
You put 5+ and ground from the Analog Sensor port to the ends of the 100Kohm pot and then put the wiper to one of the sensor inputs and you get no reading from the Pbasic or from a voltmeter?
If it is true, you either have a bad pot or you have a bad RC.
01-24-2002, 10:34 PM
As I read your post you are referring to pins 2,3,4. Does this imply you have four pins? Is this not the pot supplied in the kit? If this is the kit pot then connecting 5 volts to one outside pin and ground to the other outside pin will yield a variable voltage on the middle pin. Ground does not mean the frame of the robot but the common of the battery. Without a return path to the battery negative terminal, the wiper of the pot will be at +5 volts (or very near 5 volts) for any postion of the shaft. This is "open circuit" voltage. When no current flows through a resistance, ther can be no voltage drop. Ohm's Law V=I*R
01-25-2002, 06:28 AM
The pin references were to the pins on the RC analog in. The Pot isnt bad because I tested it out not hooked into the RC. I really hope we didnt get a bad RC. I had it hooked up to an independant power supply (5V connection we have in the electronics lab), with just the wiper going to the analog in, and it still does the same thing. When I unplug the analog pin it works fine.
01-25-2002, 07:30 AM
Did you make sure your power supply and the RC had a common ground?
No sense putting a voltage into the sensor pin if it is not with respect to the same ground voltage.
Finally, how sure are you that you have the pinout of the Dsub connector right? It is VERY common for folks to flip left and right on those 25 pin connectors. For myself, I don't buy any connector for these types of connectors that don't have the pin number molded into the connector. There are just too many ways to flip the pins around if you are not careful.
Check it out.
P.S. One more thing, check your manual to see that pins 2,3,4 are the right pins. JJ
01-25-2002, 07:45 AM
Yep, pinouts are correct. We are using the one that shipped with the kit, and it does have the pin numbers molded into it. At least ours did. And it is on a common ground with the board.
I checked with the +5V and the ground plugged into pins 3 & 4, and the wiper into 2, which are correct, unless they misprinted the manual.
I also checked with pins 5, 6, & 7 with the same results.
01-25-2002, 01:11 PM
Azash, I emailed some of the other people on your team, with some steps you might take.
Innovation First might be the folks to talk to. They are really great to work with.
01-26-2002, 09:21 AM
I think the problem is that you are using 3 wires,
because the total restance between the wiper and the 2 outside connections stays the same you have the same amount of ground all the time,
cut one of the wires loose that are supplying ground and see what happens,
really all you were doing with 3 wires is changing which pin the +5v was grounded to.
But if the manual says to use 3 pins then dont use my suggestion, I havent used analog muchk so I could be wrong.
01-26-2002, 05:07 PM
Azash and the team found their problem, and it is fixed, now. Good Work, Guys !:)
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