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  1. #1
    Hi All

    Im looking to build a new stepper driver for my mill project. The original board used an L297 driver and 2x L6203 H bridge output stage. I'm hoping to build something similar and have found a few circuits on the net.

    I have also found some nice additions to the basic circuit like overload protection for the output chips (good idea since I fried them on the last board ) and varable voltage for VREF to increase Half step torque.

    The circuit i have used i heavilly based on one I got from an old thread on cnczone but I'm unsure what the Pic chip dose (i asume it detects the clock pulse and varies the VREF accordingly)

    So Question 1. can anyone help with a replacement circuit for the PIC chip as I dont want to use PIC chips for this project.?

    And Question 2. Can some check over my version to make sure it works or suggest an alternative?

    Thanks in advance
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  2. #2
    Hi

    I'm not sure about the PIC - R23 is adjusting Vref (driven by Q2/IC5A) into it's GP4 input (which for the '675 is analogue input 3).

    But it also does take the CLOCK signal that goes into IC3 (L297).

    I don't think it's doing anything to Vref, so it must have the capability of driving CLOCK instead. Otherwise, there's not a lot the PIC could do - all the other IO pins are grounded. Do you have the code for the PIC? That would give more of a clue as to what it's doing.

    Any particular reason why in yours you aren't using optoisolators?

    D11 on yours should be a triac instead (T1 on the original, middle-bottom).

    C15 on yours is the reverse polarity (+ve is going to GND) - next to T1 on the original (C27).

    I see you've omitted the power supply circuit (top-right) - are you going to power it from the CNTL port (JP3)? I can't see any other method of providing +5V...

    Apart from that, it looks good - but I'll have another look later on.

    Edited to add: I suppose the PIC could do things with Vref - although the only things it could do are:

    - Power GP4 high
    - Power GP4 low
    - Pulse GP4
    - Leave GP4 open

    It might power down the stepper controller if the clock hasn't been used for a while. GP2 is also the INT(errupt) input on the PIC. In which case, I suppose a resettable monostable could do the same job.

  3. Quote Originally Posted by Ross77 View Post
    Hi All

    Im looking to build a new stepper driver for my mill project. The original board used an L297 driver and 2x L6203 H bridge output stage. I'm hoping to build something similar and have found a few circuits on the net.

    I have also found some nice additions to the basic circuit like overload protection for the output chips (good idea since I fried them on the last board ) and varable voltage for VREF to increase Half step torque.

    The circuit i have used i heavilly based on one I got from an old thread on cnczone but I'm unsure what the Pic chip dose (i asume it detects the clock pulse and varies the VREF accordingly)

    So Question 1. can anyone help with a replacement circuit for the PIC chip as I dont want to use PIC chips for this project.?

    And Question 2. Can some check over my version to make sure it works or suggest an alternative?

    Thanks in advance
    At a guess i would surmise the PIC is detecting the clock to the L297 and after some timeout after the last clock pulse is pulling Vref down to reduce the current in the motor. A 555 set up as a monostable with say a 5sec delay and triggered from the clock line might do the trick...

    [edit] must learn to type faster![/edit]

  4. #4
    Thanks for the replies

    Tribbles
    Im not using the optos as i plan to make modular set up with a master board for the optos. Thank for spotting the mistakes, thought it was a funny looking diode :whistling:

    The +5 is supplied from the input connector, Bottom left.

    Irving

    So is the Pic just earthing the 5v supply to the VREF making it 0v which means there is no holding current? I presume it would then revert back when a pulse is detected on the clock line?

  5. Quote Originally Posted by Ross77 View Post
    Thanks for the replies...
    Irving

    So is the Pic just earthing the 5v supply to the VREF making it 0v which means there is no holding current? I presume it would then revert back when a pulse is detected on the clock line?
    Well if that was the case it would be pointless IMHO. I had a quick scan round and can't find the original design writeup for this circuit. I am wondering if the PIC modulates the VREF rather than just shutting it off...

  6. #6
    I'd missed that connector for some odd reason

    I suspect that VREF does indeed go to 0V.

    Q2 on the original can pull it low based on IC5A, and the PIC can pull down pin 3 of R23 (original).

    I suspect that you may be able to get away without the PIC at all - it would mean that it would be powered up continually though (so you may need to get some meatier heatsinks).

  7. #7
    Quote Originally Posted by irving2008 View Post
    Well if that was the case it would be pointless IMHO. I had a quick scan round and can't find the original design writeup for this circuit. I am wondering if the PIC modulates the VREF rather than just shutting it off...
    It could do that - it would reduce the holding torque for the motors as a result. It would then provide the "full" VREF when it's being clocked. It might be a very short pulse...

  8. #8
    Modulating the vref would make sense as no holding current isnt much use. Is that why a Pic is used rather than a 555?

    I did find another cuircuit that uses logic gates to trigger 2 separates trim pots but the control signal came from an external source or the software. would it be possible to use a 555 chip to trigger this circuit?


    This would make more sense and be easier to setup
    Attached Thumbnails Attached Thumbnails 4AStepperMotorCard_V1_2.pdf  

  9. #9
    Simply dropping VREF to 0 would probably drop the output current to 0, which is probably what Q2 is being used for (I'm not familiar with the L297 itself).

    If INH1, INH2 and JP1 (pin2) are high, then VREF would be 0.

    If the PIC's modulating VREF, then it would allow the holding current to be varied - it was probably felt by the designer to be more configurable than other circuitry (and I would be inclined to agree - you could do some cleverness like make the holding voltage [current] drop off over time the longer you don't use it, and then stabilise at a set value for the minimum hold you need). C23 would smooth the signal.

    In your latest circuit, the whole left hand side appears to be doing the work of the PIC - and that's a fairly large circuit. Are you sure you don't want to use a PIC (why not?)

  10. Quote Originally Posted by tribbles View Post
    Simply dropping VREF to 0 would probably drop the output current to 0, which is probably what Q2 is being used for (I'm not familiar with the L297 itself).

    If INH1, INH2 and JP1 (pin2) are high, then VREF would be 0.

    If the PIC's modulating VREF, then it would allow the holding current to be varied - it was probably felt by the designer to be more configurable than other circuitry (and I would be inclined to agree - you could do some cleverness like make the holding voltage [current] drop off over time the longer you don't use it, and then stabilise at a set value for the minimum hold you need). C23 would smooth the signal.

    In your latest circuit, the whole left hand side appears to be doing the work of the PIC - and that's a fairly large circuit. Are you sure you don't want to use a PIC (why not?)
    The purpose of IC5,Q2 (IC4A, T1 in circuit 2) is to reduce Vref by 1/3 approx on 1/2 steps to even out torque and get a better 1/2 stepping. This is because, without those additions, the current on half steps (both coils on) is 1.4x current on a full step (one coil on) (sum of the vectors). In circuit 3 the left hand side is a charge pump that detects when the clock pulse train vanishes and switches Vref from Imax to Ihold after a short delay, however its complicated by additional circuitry to force Ihold when the driver powers up.

    Whats lacking is the actual code for the PIC, only then can we determine what its doing... should be on the net somewhere...

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