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V4 issue in extreme cold temperatures

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  • V4 issue in extreme cold temperatures

    Spring is approaching, so over the last few days I put the steering system back into the tractor. I took it out for some tuning today (first time with the v4 FB) and after about 5 minutes it locked up on me. The FB is being powered via USB, and I have no reason to believe the USB cable came loose. Disconnecting and reconnecting the DC jack did not resolve it. I had to disconnect/reconnect the USB connection to get control of it again.

    I only have relays on two of the FB outputs. One was on at the time of the lock.

    Do you have (or have you looked into) some kind of watchdog process on the PIC? If there was a watchdog, would that also kill the handle in the driver, thus requiring a software disconnect/reconnect to get control of it again?

    Should I try changing the jumper so that the PIC is powered by the DC jack instead of USB?


  • #2
    We've played with watchdogs in the past, I can put up a firmware update if you like.

    I have no idea what's going with your tractor. The PIC must be still picking up noise over the 12v line. Are you powering it the same way you powered the V3 that didnt lock up?


    • #3
      Sure, I'll try a watchdog. Is there any reason that a watchdog would be a bad thing, or why isn't it part of the standard firmware?

      In order to get the v3 to be stable in this tractor, I had to power it with an inverter, then to a 12vDC power brick. I had hoped that the larger capacitors on the v4 would resolve this. My jumpers are currently set so that the PIC is powered from USB. Since I'm using USB power, those bigger caps probably aren't doing anything for me, are they. I'll try moving the jumpers over to see if that resolves this. I'll take the tractor out for another test tomorrow.

      The only major electrical noise I can think of would be the solenoid valve I'm using to control the steering. That circuit gets power direct from the battery, with ground going to the engine block. The 12v coming into the DC jack on the FB is coming from a circuit on the main fuse panel. That circuit also powers my GPS receiver, which has worked fine all through this. I'm pretty sure that receiver is designed to accept any kind of electrical crap that could possibly be seen. It's a pretty rugged unit, and probably has some reasonably large caps inside.



      • #4
        I moved the power jumpers over to the DC powered position and took the tractor out again today. It ran for about 15 minutes, then locked up on me. I power cycled it, and it continued to work for another couple minutes before I parked the tractor back in the shed. I took a pic of what the FB looked like while locked, not that it will tell you much. I'll get that posted later tonight when I get home.


        • #5
          (removed broken links)

          Here are my pics from today. Last pic shows the locked up state, which really doesn't mean much. I have outputs 15 and 16 oscillating just so that I can see when there is IO happening. Outputs 12 and 13 each go to a relay, which control solenoids on each side of the hydraulic valve, which is under the plastic box.

          One of these days I'm going to throw an o-scope on the +12 side coming in to the FB to see how much of a power dip it is seeing when a relay trips and a solenoid powers up.
          Last edited by mx270a; 11-10-2011, 12:44 PM. Reason: removed broken links


          • #6
            Is that the motor underneath the plastic box? If so, you may be getting too hot.



            • #7
              Yes, that is the engine. Space is at a premium in the cab, and there was an empty spot under the hood. Heat may become an issue this spring/summer, but it certainly isn't right now. I'm in Iowa and it is well below freezing here. In my testing, I haven't been working the engine hard enough to start warming up the engine bay much.


              • #8
                Ohhh, did you say well below 0!. How much below. The xtal on the board might have a standard temperature range not extended.

                I had a similar problem when I was doing some capability studies for parking meter coin entry systems for Canada. The controller board actuall stopped working at below -10c (degrees) once the xtal was warm again it continued working.

                What you could do is when it stops working again, try to heat up the xtal to see if it resumes operation, if so then you can either keep the xtal warm or upgrade to a extended temperature xtal. The extended temperature ones go down to -40c

                FYI, these are the typical ranges for xtals
                -40C - +85C // Extended temp range
                -20C - +80C
                0C - +70C // Standard temp range

                If the above test fails, check the specs of the Microcontroller (though I found the micro is more tolerant than the xtal)

                Hope this helps


                • #9
                  Well the board was 60 degrees F in the shop before I took the machine out for testing. The FB is in a plastic box which I maybe had the lid off once before it locked up. Outside temp was about 14 degrees F, but when it locked, the engine had been on for a bit so the air around the plastic box would have been slightly warmer than ambient temp. Probably at freezing or just above. Once I power cycled the FB, it kept working for the rest of my testing, which was only a few more minutes.

                  What is the xtal? Is that the 5v regulator?



                  • #10
                    Oh sorry, thats the oval silver thing right next to the bootloader button. xtal actually stands for "crystal" its job is to oscillate the microchip at 20.0Mhz (you should see it printed on top of it)

                    If ambient is 14C F, thats about -10C celsius

                    Thats means if the Xtal was a "Standard temperature range" type it would be out of spec.

                    Sorry the above ranges were in Celsius, metric down here


                    • #11
                      I put the power inputs of the card on an o-scope today with the relays clicking away, and I don't see anything that looks odd. Seems to me this has to be a voltage issue, so now I'm a bit confused. If that is the case, then it doesn't make sense that the card locked while running on USB power? Is the PIC power isolated from the power used for the output drivers?


                      • #12
                        Does you entire system work (without locking up) when not in a really cold environment?
                        If so, then it will be a temperature issue.

                        I would make sure that everything works first at "normal" temperature before subjecting it to a harsh environment.



                        • #13
                          In all the testing I have done here at the house (on a regular 120vAC to 12vDC power brick), I have never once had it lock up or do anything odd. In the limited testing I've done with it on the tractor while parked in the heated shop (running on battery 12vDC), I've never had it lock up. The only two times I've had it lock up are when I'm outside and the tractor is running, which have both been days with temps below freezing.

                          If it is a temp issue, that would explain why it locked up when powered by USB. If it is a voltage issue, the PIC should remain powered via the USB.

                          What is odd about the temp theory is that last time when it locked up, I pulled the cover off the plastic box to unplug/reconnect the DC power jack and take a picture. That would have allowed the board to cool off further, and it should have locked up again. I only ran the card another ~4 minutes outside after that, so it wasn't a good enough test.

                          I'm thinking I need to take the rig outside on a cold day and let it set for a while with the FB active to see if I can get it to lock up. If it does, then I know it is a temperature issue, not a voltage issue. Forecast for tomorrow looks to be about as cold as before, so that should be a good test.

                          Greenman, when the PIC is powered by USB, is the crystal also being powered by USB?


                          • #14
                            If its a temperature issue it doesn't matter if the unit is powered from USB or 12v.

                            "USB only" power is only useful for running the FB when 12v is not required. Though you would need an external power source if you want to use 12v relays! So you might as well run it off 12v in this case. If you entire system runs of 5v only then a "USB only" power is handy (set by jumper).

                            P.S. Im sure Greenman will say the same - If the FB has power, the crystal has power! No matter if its powered from USB or 12v.

                            The only thing I would suggest now is have a little heater running in your box just to keep the FB warm as an experiment. If it doesn't "lock up" after a long test, then I would upgrade the crystal then do the test again.

                            To be frank, I don't think the FB was intended to be operation at really low temperatures. I'm sure Greenman can confirm this.

                            *Note: If you want to reliably use the FB in a really cold environment for extended periods of time there are more things you have to consider.



                            • #15
                              Well you had V3 running no problems with an inverter setup right?

                              Can you put it back on the inverter and see if it works fine?
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