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Quick question about my mills BOB

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  • Quick question about my mills BOB

    Hey folks, I am still using my mill with the old retrofit I did while I very slowly plod away at the servo conversion... I had a job come up that I finally decided to rig up a digitizer for, however, I have hit a bit of a snag. I am currently using a CNC4PC C11 BOB from some years ago. It is a revision 6.2 IIRC. Anyhow, my board has the inputs pulled low instead of the more recent revision which has jumpers to select low or high. Anyhow, to do this probe, I need the input pulled high and the probe pulls to ground. My question is, can I just keep trying lower and lower values of pull up resistors until I get it to overcome the internal pull downs? IF the board was in a better spot I would track down the pull down for this input and remove it, but I would have to take the whole thing apart to get to it. I have a question submitted to CNC4PC but I kind of need to get moving on this. Any help is appreciated.

    Thanks,
    Jason

  • #2
    Well, trial and error prevailed. A low value pull up resistor did the trick. I settled at 330 ohms 1/2 watt. Seems to be working okay.

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    • #3
      I'm not convinced this is the final solution. If I pull this input up with 330 ohms it initially works, but not long after, Mach started to show input 15 (the probe input) as active with the pin pulled high and the pin set as active low. The pin is clearly still high, there is an LED on the BOB for each input and it shows it high, but in order to get it working after I initially reported success I had to switch the input setting to active high. I suspect that I have screwed up one of the logic inverters on the board. Arturo, the guy who apparently designed this board, told me that I could pull it up with 4.7K resistor. That didn't work, I started at 10K and worked my way down to 330 ohms before I got it to pull high.

      On top of my oddly inverted input, I also began having trouble with the "Y" axis output from the BOB. I had a few times while setting up the probe where Y axis just quit making moves. The drive kept the motor locked, but acted like it was not getting any commands. Power cycling the BOB and it started to work. I then found that Y would make long rapid moves okay, but any very short pulse length would not produce any movement at all. For example, If I set the jog mode to step and set the step to .001, the Y axis motor twitches very rarely, but it never make a full move. All other axis work fine on .001 step per jog. I switched wiring around and eliminated the drive, the drive works fine when getting input from another channel. I moved the Y axis to the A axis and output to get on with the job, and it has been working fine on there.

      I can't help but think that I have got something screwed up on the board, maybe directly related to the probe pull up. I asked Arturo if he knew what the issue could be and he has been singularly unhelpful. He first told me he doesn't have any manuals for my board revision and then he suggested a pull-up that did not work. Then when I asked about the Y channel flaking out he told me it could be any number of things and I should buy his new version of the board. It will be a cold day in hell before I another board from someone who has so little interest in supporting his product. I realize it's not brand new, but it is functionally identical the new models, and there is no reason to replace it. I was hoping he would just tell me Rxxx is the pull down for pin 15, remove it and put in an external pull-up. As the original designer it would have taken him very little effort to look it up and tell me, but whatever. I am going to have to pull the board after this job and track down the pull-down and see if I can figure out why the Y channel is fubar.

      The sad thing is that this board was designed with repairability in mind. All the inverters/level shifters/opt-isolaters are in sockets and it will probably only take $5 in ICs to replace all the possible culprits. I'm really dissapointed in the reply I got back from this company today.

      Thanks,
      Jason

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      • #4
        The older board detail shows the five 4.7k pull downs for each input in front of the input terminal strip. R2 to R6?
        You also confirm this with a meter.
        Max.

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        • #5
          I suspected those were the pull downs, but the board is in a pretty bad spot for crawling under with a meter and probing. Anyhow, when I get it pulled out I will confirm, but thank you for the insight.

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