regulated power for potentiometer

*Apologies if this question has already been discussed in detail in another thread. A quick search returned no helpful results.

What is(are) the recommended way(s) to power a potentiometer so that the signal is less affected by battery voltage change?

Would it be helpful (and legal) to tap into the power going to the radio?

Or perhaps do A/D on both the signal and the power to the pot, and use the ratio?

I believe the converter on the Analog Breakout is pretty good at handling low battery voltages. My experience with it is limited, so YMMV.

It’s definitely not legal to connect anything to the radio power slot but the radio/radio converter.

That’s a good question. I know our code last year used “getAverageValue()” and seemed to be very consistent - our arm (controlled with 3 pots - shoulder and elbow using 270 degree pots, and winch using a 10-turn pot) didn’t seem to be affected by power, at least not until the power got so low the motor on the winch couldn’t get the robot all the way up. In our build space testing, we saw no visible difference in how the arm operated when going from a dead battery like that to a fresh, fully charged one.

It’s very easy to add a jumper to the analog board and read in the supply voltage. Since it’s a 0.1" pin header, you can just use a standard 0.1" jumper between the center (5v) and signal pins.

That’s probably the easiest way to do it.

The Analog Breakout has an LDO 5v linear regulator, good to about 5.6 volts. Do you know a team who is getting that low consistently?

Us. At least this appears to be the problem.


Do your driver station logs show you getting that low in a match?

I wasn’t suggesting connecting anything other than the 12-to-5 converter to the PDB regulated 12v.

You also aren’t allowed to power anything but the wireless bridge from the regulated 12v slot. [R43]

Toward the end of some matches, yes.

If you’re having trouble with the Analog Breakout, the Digital Sidecar isn’t far behind, with much worse symptoms. It might be helpful to make a new thread about how you’re killing batteries over the course of a match, and describe your robot and power systems so that people can provide suggestions on how to reduce power draw.

The dropout of Analog Breakout regulator decreases as the load decreases. You may be able to reduce the number or size of loads to gain a little more margin. See attached chart from the MIC5209 datasheet.

I agree with Max that you can’t tap into the radio power supply in any way.

One option, without adding an external boost converter, is to use power a Solenoid breakout with cRIO 24v (allowed per R42). Turn on a Solenoid Output (allowed per R51), and then use a voltage divider to bring it down to 10v (The NI analog module is +/-10v). This has the disadvantage that you can’t read the pot during disabled mode. You’re also switching from a linear regulator to a switching regulator.



Could you wire the positive terminal of the potentiometer to the 5v port on the PDB? I’m not sure how low of a battery voltage it takes to brown that port out, but I don’t see anything against it in the rules.

Can’t you use the voltage regulator for the camera? I think that is legal

I’m shocked that you’re having this problem and we have not run into this. My team has a penchant for using a TON of motors (13-15) and at least 3-5 pots each year and we haven’t run into this. Plus our driver drives like a bandit and we have our 6 CIM drive geared to the moon this year so I know we’re sucking some serious juice out of the battery. We do buy ten brand new batteries every year and use a freshly charged battery every match which helps us.

Any major mechanical inefficiencies in the system?

Are all your crimps and terminals good? Anything getting super warm?

Have you tried swapping the analog breakout?

It may just be old batteries.

Aaron, when’s the last time you guys capacity-tested your batteries?

So they’re calling a 10K pot an “electrical load”?

It’s more like a reference voltage.

Oh, well.

I don’t make the rules. :smiley:

All brand new batteries. I’m not the programmer, so I’m just told that we are having this issue with the potentiometer.


Can I see a driver station log where you drop below 6 volts?

I’ll email our programmer and ask him to post it or send it to you. Due to work schedules, it likely won’t be available right away. Thanks for following up with this.