Jrk 21v3 analog input . Rx pin issue?

Hi to all,

I recently bought a jrk 21v3 MC and the LACT8P-12V-20 Linear actuator w/feedback.

I had some little issues getting off the ground a couple weeks ago and talked to support. But then had to leave it all until two days ago.

2Days ago I brought it all into my house and laid it out. Actuator, jrk21v3, analog pot and a 12v battery, along with it’s .9amp charger.

Taking my time with the config utility I was able to easily get the jrkv3 up and running, responding well to my 10k pot input.
Fwd/back, etc. All good!
Today I did the same thing, just reading about PID and tuning , etc. All good.

I then took my system apart, took it outside to my application and hooked everything up. When I powered it up. The Linear actuator took off in the extend direction all the way to the limit switches.

I checked, rechecked, etc. Then decided I had to bring out my laptop and see the issue via the config utility.

Hooked up the laptop and found I had lost my analog-input. Gone. Sitting @ zero.

I checked several things outside and then decided to bring it all back in and lay it all out.

As it is now, I have no controllable analog input. The analog input rapidly fluctuates between 12-16.

I have tried different pots. I have tested via multimeter the v+ and grnd- from the analog pins @ my pot and all is well there.

There seems to be a problem on the rx pin?

I don’t know what else it could be and just as importantly I cannot for the life of me figure out how I killed that function.

I wasn’t in a hurry. No dangled wires. All wires have connectors on them to aid in prevention of inadvertent shorts.

Please advise?

thanks, tom_w

Some omitted interventions.

  1. When I realized via the config utility I had a problem, I immediately reloaded the .txt basic file/dumped my new tuned saved file.
  2. The jrk seems to do everything else it was doing before and was designed to do in serial mode.
  3. In analog mode the yellow light is lit and blinking very fast letting me know that it knows that there is a target that it needs to reach.
  4. Only other light lit is the green one when my USB is hooked up.
  5. All errors clear.
  6. I have dumped the .txt and reset the jrk to the as delivered program and re-uploaded the basic .txt file twice ( all via serial/usb).

my apologies for forgetting to mention these items.


It sounds like you spoke to one of our techsupport staff over the phone today. For anyone else reading this with the same problem, one check you can do is to see if your jrk is capable of reading the analog voltage on the RX pin. A simple way to do this is to open up the Pololu Jrk Configuration Utility, click the graph in the top right, and enable the Input, Target, and Feedback signals. You can then vary the analog voltage on the RX pin to see if those signals respond. If they do not, the voltage is not being correctly read by the microcontroller. In that case, it could be damaged.

- Grant

Yep. Easy to both check and see that the input values are there, or not.

Mine simply lost it’s ability to differentiate on that RX line. And there is no good reason why.

There are many possibilities, but the probabilities are low. My preference would be that it is something I did.
Because I control that variable.

Main reason the probabilities are low is, that wonderful BIG-RED battery disconnect I use on my application.
Everything in it’s place before turning that switch.
Oh, problem? Fine.
Turn the switch off before doing anything.

That switch may not seem like a big deal to anyone but me. But it was designed into this system to prevent the probability of +/- wires coming into contact with things they ought not while live. Another habit to consider is the placing of male/female connectors so that nothing gets connected to it’s complimentary part that isn’t meant to. Not always doable, but good habit.

Like I said to the the tech on the phone yesterday: I’ve smoke-checked enough stuff in my lifetime.
My Junk pile over that time is huge.
And if you’re doing anything, building anything, that is normal.
The only variable that I control is me.

thanks, TOM_W

ps: that tech was super good and easy to work with.