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  1. #1
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    Default Pokeys57cnc board questions

    Hello all,

    I was wondering if anyone is using a Pokeys57cnc board and could answer some questions. I am retrofitting an new to me milling machine and am trying to create a front panel control board. I would like to incorporate spindle speed and feed speed over ride. I was hoping to use the analog inputs on the Pokeys board with a potentiometer for each.

    My first question is is it possible? Can this be done in Mach3 and can anyone help with the filter math? Below is the only information I can find in the manual.

    7.6. Analog inputs
    Analog input function is only available on pins 41 to 45. These analog inputs can also be freely mapped to any of the 6 joystick axis; X, Y, Z, rotation X, rotation Y and throttle.
    Analog inputs have a resolution of 12 bits and are sampled at a fixed rate of 10 kHz, then fed through adjustable digital low-pass filter with the following equation 𝑦(&#119896=𝑦(𝑘−1)∗𝑓𝑖𝑙𝑡𝑒𝑟𝑓𝑖𝑙𝑡𝑒𝑟+1+𝑢(&#119896∗1𝑓𝑖𝑙𝑡𝑒𝑟+1
    where y(k) is the output analog value, u(k) is a new A/D sample and filter is a user-adjustable constant. For proper operation of the digital filter, an analog low-pass filter with a cut-off frequency of 5 kHz must be used on each analog input. The following equation gives the relation between value of filter and filter’s cut-off frequency: 𝑓𝑐=10 𝑘𝐻𝑧2𝜋∗𝑓𝑖𝑙𝑡𝑒𝑟
    Sample u(k) is produced according to the following equation 𝑢(&#119896=𝑈(&#119896[𝑉]3.3 𝑉∗4095
    where U(k) (in Volts) is a voltage present on the selected analog input pin.



    Algebra was over 35 years ago and I don't remember much.

    The over ride buttons in Mach3 are a format string and I am wondering if they would need to be modified? Or am I approaching this wrong and should be using PWM with a percentage?

    Thank you for looking and any direction you can offer,

    Jeff

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  2. #2
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    Default Re: Pokeys57cnc board questions

    I really love making these of projects, from analog to digital and digital to analog hehe, there`s an easy way to use a joy stick without hacking on the board itself sir, it`s a software based control which I used almost everyday to zero on materials I cut, keyboard to joystick mapper, then you can map the 12 buttons there according to your preferences, you can even create a macro keyboard combination to control some specific buttons on MACH3

    Once you configure it you dont need a keyboard anymore, just autostart the mapper software everytime the PC starts.



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    Default Re: Pokeys57cnc board questions

    I don't know if you solved your question, but my recommendation would be to buy a Pendant to accomplish these two tasks. I think you will find that a manual override may interfere when you are running the mill in full CNC mode where Mach controls the speeds.

    A Pendant will give you those controls plus much more.

    To answer your question, you can do what you are thinking of using the Analog input pins. I can't help with the filter math.



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    Thumbs up Re: Pokeys57cnc board questions

    Quote Originally Posted by maxspongebob View Post
    I don't know if you solved your question, but my recommendation would be to buy a Pendant to accomplish these two tasks. I think you will find that a manual override may interfere when you are running the mill in full CNC mode where Mach controls the speeds.

    A Pendant will give you those controls plus much more.

    To answer your question, you can do what you are thinking of using the Analog input pins. I can't help with the filter math.

    Where do you get the Pendant you are referring to? Thanks



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    Default Re: Pokeys57cnc board questions

    Are there any defaults given for the filter constants? If so I'd just go with those and tweak them if you have noise issues. Potentiometers for this use have very low effective frequencies, so you aren't likely to have any issues with the filter being too aggressive.

    For the analog filter, I think I'd go with a single pole RC filter. Capacitor connected between the input and gnd, and the resistor in series between the wiper of the potentiometer and the input. fc=1/(2*pi*R*C). fc should be less than or equal to 5kHz (I don't think there would be any harm having it much less than 5kHz.) I'm not sure what to pick for R, I think probably something similar to the value of your pot. So if 10k, I'd go with around 8nF for 2kHz cutoff.



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