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Potentiometer to ms input, brain fart.

linuxman51

linuxman51

Railspeeder Enthusiast #1
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Dec 25, 2002
Location
mont, AL
Think I'm having a brain fart on this, as I don't believe the issue should be that difficult.. Have basic potentiometer, am using it for a sliding input (analog 2) to the ms. I'll double check, but I'm fairly certain I have 5v going in one side, and the input to the ms going out the other.

It does work, however, it keeps dropping out.. The spikes go up with the knob, but it looks more like jagged teeth than a smooth linear input.

Is this a case of ****ty POT (lol), or have I missed something obvious like a pullup/pulldown inline resistor, etc? I was skimming the pro manual this morning and couldn't find that particular topic covered, though knowing how the ms documentation is organized, it'd be a footnote somewhere that I missed.
 
A normal potentiometer (or throttle position sensor) will have three terminals. Two terminals will be hooked to either end of the resistance element and the third terminal will be hooked to the wiper that slides along the resistance element.

I'll double check, but I'm fairly certain I have 5v going in one side, and the input to the ms going out the other.
Click to expand...

I don't know whether you intended this; but, that kind of implies only two connections to the TPS. There needs to be 3 connections from the pot / TPS to the MS. The 3 MS terminals for the TPS will be:
- regulated 5 volts
- sense line
- sanctioned ground

The regulated 5 volts and sanctioned ground need to be connected to either end of the resistance element. The sense line is connected to the wiper. As you rotate the TPS / pot you should get a smooth voltage increase form 0 to 5 volts (or 5-0 volts) on the sense line as you rotate the pot. No pull up resistors involved.

If you just omitted mentioning the ground reference and the voltage you are measuring on the sense line does not increase / decrease smoothly as you rotate the TPS them the TPS is merde.
 
142 guy said:
A normal potentiometer (or throttle position sensor) will have three terminals. Two terminals will be hooked to either end of the resistance element and the third terminal will be hooked to the wiper that slides along the resistance element.



I don't know whether you intended this; but, that kind of implies only two connections to the TPS. There needs to be 3 connections from the pot / TPS to the MS. The 3 MS terminals for the TPS will be:
- regulated 5 volts
- sense line
- sanctioned ground

The regulated 5 volts and sanctioned ground need to be connected to either end of the resistance element. The sense line is connected to the wiper. As you rotate the TPS / pot you should get a smooth voltage increase form 0 to 5 volts (or 5-0 volts) on the sense line as you rotate the pot. No pull up resistors involved.

If you just omitted mentioning the ground reference and the voltage you are measuring on the sense line does not increase / decrease smoothly as you rotate the TPS them the TPS is merde.
Click to expand...

It's not a tps, just a variable input (vs rotary switch). I'll go dig up the things and see what it is exactly that I ordered (and wired up) years ago.

Fake edit: it is in fact, a 3 wire. leaning towards it being junk.
 
and going back and checking reviews on them, apparently that is not uncommon. Well hell, I didn't think I was cutting corners on that deal, oh well haha
 
linuxman51 said:
and going back and checking reviews on them, apparently that is not uncommon. Well hell, I didn't think I was cutting corners on that deal, oh well haha
Click to expand...

Sounds like (again in guitar parlance) a scratchy pot.

Two options:

Spray some deoxit inside and work the pot a few times. Sometimes that helps

Or

Replace with a better quality part: CTS, bourns etc.
 
the thing is pretty much brand new (not in age, but use), I'm fairly certain at this point it's just a piece of ****.
 
I'd check the pot with a multimeter or scope set to a very slow sweep rate (or roll if it's supported) and cycle the pot a few times. The 3 pins should be ground, wiper to MS, +5v.

If you're only using the pot for a select input, you can hang a capacitor off the wiper-to-MS wire that will help smooth out the noise/chatter. Try anything in the 1uF to 100uF range and see if it works OK (one side of cap to ground, other side to wiper; if using a polarized cap, + goes to wiper).
 
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