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  1. #11
    Hi Robin

    Thanks, i'll give it a go, can you recommend a particular NPN transistor, and what is the Resistor rating for the one in front of your 5v mark.

    Regards

    Ray

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  3. #12
    Hi Jazz

    You know i think that i am a newbie to this world of CNC / Electronics. As previously mentioned i have a ZP54 - int Breakout Board, would you have a drawing for the HOME position switches or do they have to be configured in Mach 3 as software limits with the Stepper motor positions. I understand how this would work with Servo's but not Steppers.

    Regards

    Ray

  4. #13
    Ray think you may be mixing up soft limits with homing and physical limit switches. Soft limits have nothing to do with Actual physical limit switches they are just a software version of a limit switch and use the machine coordinate system has reference.
    In fact with soft limits defined which you usually setup to be just less than the machines physical hard stop range then it's very easy to crash the machine into the hard stops because when you RefAllHome without Physical Home switches Mach just Zeros out Machine coords where ever it's parked.
    So if you happen to RefAllHome with the table or Gantry say towards the middle of movement range then Mach use's this Zero coord has the start point for soft limits and if for instance you set-up soft limits with a movement range of 500 positive before soft limits kick-in but you only have 400 physical movement left then Mach won't know and crash into stops.!!

    Soft limits have absolutely nothing to do with home switches at all other than they share the same setup menu in Mach.

    Personally I use separate Limit switches wired in series using one input on the Bob. Then have separate Home switch's wired in series using another input of the BOB.
    You only need 1 home switch per Axis.

    To set-up Home switches in Mach first set the input your using in Ports&pins/input-signals. You really have 3 options now.
    If sharing LIMIT switches has home switches then set each Axis Home signal to the same input your using for limits from the BOB.
    Same has above for separate Home switches if your using them wired in series just using the different input from BOB.
    If using individual home switches then you'll need to set each Axis signal with the individual Input used on BOB.

    Next in the Home/soft-limits menu set which way you want the machine to set off looking for the home position using the HomeNeg selection.
    In this same Menu you can define other things like auto zeroing the DRO's after hitting switch and percentage of Rapid speed to home at.

    Thats all there is too it.
    Last edited by JAZZCNC; 29-12-2012 at 02:24 PM.

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  6. #14
    Hi Jazz

    Many thanks, you are both right and wrong. I may be a bit confused, but in the days when i had to work for a living, i can remember,that on our robots, we had physical limit switches (Usually Proximity Switches) to prevent the machine from crashing when being used in MANUAL MODE. The HOME position was a position set in a separate program just for re homing the machine to it's start position, this is what i would like to do on my machine, not because it needs it, though i do appreciate it needs some degree of safety, it's just that i would like to do it, after all when i have finished the machine i have no production targets just there as a Hobby.

    Regards

    Ray

  7. #15
    Quote Originally Posted by manofgresley View Post
    can you recommend a particular NPN transistor, and what is the Resistor rating for the one in front of your 5v mark.
    I am a dinosaur when it comes to transistors, how about a BC547.

    Assuming 20mA to drive the LED and a 1.2 Volt drop across it, about 190 Ohms for the resistor.

    I drew it up to minimise the component count, when the transistor switches on the Volts it has to play with fall away, may need a third resistor so don't lay any PCB's until you have tried it.

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  9. #16
    Quote Originally Posted by Robin Hewitt View Post
    Assuming 20mA to drive the LED and a 1.2 Volt drop across it, about 190 Ohms for the resistor.
    Personally I'd have gone with a resistor for each LED (to get their respective brightnesses balanced right)...therefore I'd connect the common anode direct to 5V & then place a current limiting resistor in each of the the LED cathode legs (the fwd voltage of a red led is about 2V, whereas a green led is about 3.2V ...therefore to get the right level balanced you'll likely need different value resistors).

    Also 20mA - depending on LED - is gonna be very bright, I'd have aimed for 10mA or less.

    Edit: Actually the way Robin has drawn it, for the red led you'll get a drop across the tranny itself, which pretty much balances the fwd voltage difference out for the red & green LEDs, so you may get away with a 180R single resistor for both....a 180R resistor will yield about 10mA through the LEDs
    Last edited by HankMcSpank; 29-12-2012 at 09:09 PM.

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  11. #17
    Quote Originally Posted by HankMcSpank View Post
    Personally I'd have gone with a resistor for each LED (to get their respective brightnesses balanced right)...
    That would get around the Volts falling away when the transistor comes on problem nicely and let you tinker with individual brighteness. Good idea.

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  13. #18
    Hi Robin
    My apologies if my protocol is incorrect.
    I have attached a PowerPoint Drawing, which is my interpretation of your drawing, which contains everything i know so far. Would you be kind enough to go over it, and advise me if it would work or not?

    Regards

    RayClick image for larger version. 

Name:	Led Circuit.JPG 
Views:	209 
Size:	38.3 KB 
ID:	7794
    Last edited by manofgresley; 30-12-2012 at 05:54 PM.

  14. #19
    So you don't have a seperate ground.

    That means every LED up stream of the one that goes red will go out.

    If you accept that limitation, dump the transistor and the 10k resistor, not required.

    Connect one LED cathode to NO, one cathode to NC and the common anode to your 190 ohm off 5V.

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  16. #20
    Quote Originally Posted by Robin Hewitt View Post
    Okay, attempt #2...
    Sick sick drawing skills there Robin!

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