Potentiometer problems

[rachal]

We have a strange issue with our pots.
Situation:
The potentiometers are wired properly, Power to pin 1, Signal to pin 2, Ground to pin 3, and connected to a PWM connector. We have tried this with 3 separate potentiometers, and they work properly when examined with a Digital Multimeter. However, when connected to the Robot Controller, a strange thing happens. The potentiometers start out giving the value off them as 70, however their output rapidly drops down to around 40, and then starts dropping slowly. The drop appears to be a logarithmic function. We've checked that it's wired to the proper port, plugged in the right way around, wired to the right pins.

Is there anything you can think of that would cause this kind of behavior?

[Kev]

pots go into Analog inputs, don't they?

[Racer26]

Are you reading the pot using Get_Analog_Value(rc_ana_inxx);? if you're not, and not using kevin's equivalent, that might cause it. Also, I would check for any debris that might be shorting something on the RC.

[billbo911]

Originally Posted by rachal

We have a strange issue with our pots.
Situation:
The potentiometers are wired properly, Power to pin 1, Signal to pin 2, Ground to pin 3, and connected to a PWM connector. We have tried this with 3 separate potentiometers, and they work properly when examined with a Digital Multimeter. However, when connected to the Robot Controller, a strange thing happens. The potentiometers start out giving the value off them as 70, however their output rapidly drops down to around 40, and then starts dropping slowly. The drop appears to be a logarithmic function. We've checked that it's wired to the proper port, plugged in the right way around, wired to the right pins.

Is there anything you can think of that would cause this kind of behavior?

Check your backup battery.

From the RC Reference Guide:

The Battery Backup circuit also supplies power to the center pins of the PWM OUTPUTS,which is required to operate servos

.

[rachal]

Okay, we hooked it up to a scope and it looks like the limit switches were grounding all the analogs when they were hit. I'll post again if the problem is elsewhere.

[billbo911]

Originally Posted by rachal

Okay, we hooked it up to a scope and it looks like the limit switches were grounding all the other analogs when they were hit. I'll post again if the problem is elsewhere.

OUCH!!!
Limit switches go to Digital inputs.

[rachal]

Oops, never mind

No, the limit switches were plugged into digital and the pot was analog, but the limit switches were shorting the entire RC

[billbo911]

Originally Posted by rachal

Oops, never mind

No, the limit switches were plugged into digital and the pot was analog, but the limit switches were shorting the entire RC

Are your switches shorting +5vdc to GND?? Not good!
Switches need to be wired between SIG and GND.

[SuperBK]

Are the pots linear taper? Check with an ohmmeter with no power to it.