Help! DIY 4 amp L297/6203 driver

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 :smile:) 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

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.

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Originally Posted by Ross77

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 :smile:) 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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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]

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?

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Originally Posted by Ross77

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?

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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...

I'd missed that connector for some odd reason :smile:

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).

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Originally Posted by irving2008

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...

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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...

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

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?)

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Originally Posted by tribbles

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?)

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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...

I'd forgotten that 410R resistor off of Q2. That makes sense.

I didnt want to use a PIC at this stage because I havent used them before and didnt want to have to learn how now. Looks like I'm going to have too tho as I'm struggling to fit it on the 3" x 4" demo board in eagle

So is the Burger cuircuit no good then, Sorry for being thick :smile:

The orignal thead was [ame="http://www.cnczone.com/forums/showthread.php?t=44802"]Problems with stepper driver (L297 and L6203) - CNCzone.com-The Largest Machinist Community on the net![/ame] but as its 3-4 years old I didnt see much point in posting

And the link is to a polish site, which obviously I havent got a clue what it says http://forum-cnc.pl/index.php?topic=55.0

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Originally Posted by Ross77

I didnt want to use a PIC at this stage because I havent used them before and didnt want to have to learn how now. Looks like I'm going to have too tho as I'm struggling to fit it on the 3" x 4" demo board in eagle

So is the Burger cuircuit no good then, Sorry for being thick :smile:

The orignal thead was Problems with stepper driver (L297 and L6203) - CNCzone.com-The Largest Machinist Community on the net! but as its 3-4 years old I didnt see much point in posting

And the link is to a polish site, which obviously I havent got a clue what it says http://forum-cnc.pl/index.php?topic=55.0

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Yes I found that too... I couldn't find anything in English relating to the original design

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Originally Posted by irving2008

Yes I found that too... I couldn't find anything in English relating to the original design

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However a google translate on post #3 'version 2006.04.26' throws up:

"

• -circuit protection -> T1
  -reduction system DC ... after inactivity -> PIC
  Power-split

"
So that confirms what the PIC does... but no info on the code... I wonder if this was ever built?

Dam I tried google translate and it came up with a load of rubbish.

Do you think it might not be worth pursuing? I saw the first few designs that didnt have the pic so I presumed it would work without it but the idea of reducing the hold current sounds like a good idea given the buzzing and noise that I got last time.

Unfortunately, without the code for the PIC, it'll be effectively useless - it would be possible to write something, but it would probably need a bit of tweaking to get it right.

I'd be tempted not to use it at all and see how you get on. The motors would get hotter because the power will be on all the time.

I like Eagle, but I got fed up of the small board size (which is their aim, I suppose), so I bought the professional edition in the end - which also gives multi-sheet schematic entry as well. I did manage to make a board wider than the maximum size, but I had to use vias for PTH pads, and be really careful about the positioning of the other components.

I'm just having a discussion with Farnell (who bought CadSoft) about getting the autorouting package for it as well (I only got Layout and Schematic, but now I want to get the complete package).

Shouldn't be too hard to create the same effect without the PIC. I see a monostable to define the timeout, and an astable with variable on/off ratio to provide a modulating switch. Could be done with the two halves of a 556 I reckon...

Then again, why not just pull Vref down rather than modulate it?

I will think on it...

I think you'd want to modulate it in order to adjust the holding torque.

But you're right - a 556 would provide the timeout and the reduction in torque. Although a 555 and a suitable transistor/resistor should pull VREF down to a suitable amount (much in the same way that Q2 does it).

Hell, you may even get away with a simple RC timer - assuming the clock's quiescent voltage is 0. That I'd need to think about (analogue electronics isn't my forté).

Thanks for the input, most appreciated.

The mono stable and astable idea sounds good but beyond my capabilites so I will have to wait for your input :beer:
I found a circuit that uses a 555 to pull vref down after 10s, its from a unipolar design that uses an L297 so i presumed it would be ok.

I'm not sure if I fully understand the timing delay, I presumed that the control circuit would activate the lower vref so soon as the clock stopped? but looking at this I think it only works after 10s of inactivity. so in most cases the current will be full power?

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Originally Posted by Ross77

Thanks for the input, most appreciated.

The mono stable and astable idea sounds good but beyond my capabilites so I will have to wait for your input :beer:
I found a circuit that uses a 555 to pull vref down after 10s, its from a unipolar design that uses an L297 so i presumed it would be ok.

I'm not sure if I fully understand the timing delay, I presumed that the control circuit would activate the lower vref so soon as the clock stopped? but looking at this I think it only works after 10s of inactivity. so in most cases the current will be full power?

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The delay could be made adjustable, but that circuit would do the trick. It needs a lot more parts than the PIC, that is the attraction of using the PIC...

I dont think a PIC program would be hard to create, using a 16F84 or equivalent...they are only a few pence now and programming them isn't hard (I can do it, so can at least 2 or 3 others)

Thanks Irving, Is that an offer to create the code? :clap:

I have a programmer that I bought many years ago, but never built, that supports that chip. So the final decision is wether to include the short cuircuit protection as it dose complicate the board a tad. Is it really worth the hassel? I first thought it was also an internal overload but after finding the application sheet it is only for output short circuit, maybe I'll just have to be carefull with the motor wiring :whistling:

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Originally Posted by Ross77

Thanks Irving, Is that an offer to create the code? :clap:

I have a programmer that I bought many years ago, but never built, that supports that chip. So the final decision is wether to include the short cuircuit protection as it dose complicate the board a tad. Is it really worth the hassel? I first thought it was also an internal overload but after finding the application sheet it is only for output short circuit, maybe I'll just have to be carefull with the motor wiring :whistling:

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I'll have a think on it...

Which bit of short circuit prtection?

I'd use the 12F675 (or possibly 12F629, which is the same as the 12F675, except doesn't have the A2D converters) - the 16F84 is significantly larger than needed (only 2 of the IO pins are required), and also needs an external oscillator.

10F20x doesn't have an INT input, so I'd discount them (although there's nothing stopping you from polling an IO pin instead of waiting for the interrupt signal).

I've got some spare 12F683s from a project I didn't need them for - they're similar to the '675, except have a PWM output capability (I was going to use them for a fan speed controller).

I'd be willing to program one up and send it on - but I'd feel a little uncomfortable doing the code without knowing exactly how it's meant to work (willing to discuss it though).

Wow thanks guys, thats a great help, now if i could just get someone to convert the schematic to a pcb and mill it for me.....:lmao:

Irving
The short circuit protection is for the the output chips, (see below)

Tribbles
Thanks for the very kind offer, Unfortunatly I have no idea where to start with the code. I can only guess that an output needs to modulate (or switch low) the vref line to set the hold current (possibly adjustable from a trim pot) and then an input needs to look for the clock pulse to reset full current when a signal is seen?

I would imagine that the timing's are going to be the hardest bit as it might loss the first step whilst switching back to full current?

Is there any reason why this couldnt be put on a separate board and just send the Vref lineto the driver board with the other signals?

Thanks again

Well lets think this through...

Whats the slowest meaningful step rate, 1 step/second? how long after the last step do we want to wait, 10 seconds?

So every time there is a clock pulse, reload an 'n' second counter. when the counter reaches 0 start a PWM output with a frequency of 100Hz say, and a mark/space ratio controlled from 2 dip switches giving 100 (off), 75, 50 and 25 settings

Use a couple more DIP switches to set the initial delay 'n', say 20, 10, 5, 2 seconds.

Pseudocode:

Interrupt routines:
If INT0 (external)

read delay value
reset main counter to delay value
set PWM output high (open collector)
reset INT0
return

If INT1 (main counter reached 0)

read PWM value
initialise PWN registers
start PWM running
reset INT1
return

Main program:

set PWM frequency
set PWM output high
configure counter clock divider
configure INT0 on external trailing edge
configure INT1 on counter timeout
read delay value
reset main counter to delay value
enable INT0
enable INT1
halt

obviously, depending on the chip used you may have to synthesise the PWM function with counters and a lookup table to determine the correct counts for each DIP setting.

I wont pretend to understand that, but it looks impressive, cheers

Any tips for laying out pcbs in Eagle or is it practice makes perfect? this could take a while.....:rolleyes:

er the ones that always hits me, repeatedly, I am not learning. Everything looks much smaller when it's actually on a pcb, smaller than the screen that is. So those neat narrow little traces and tiny pads are even smaller than you thought. oh and make the holes in the pads very small as large ones make soldering not as neat and the drill won't center aswell. Well those are things I need to remember, but don't till I am looking at the laser print.

I seem to remember Mariss from Gecko offering to sell cplds programmed pretty much as in the geckodrives, for something like $5 a time?
It was mentioned in the looooong thread about the Alegro A3986 chip that everyone decided didn't work properly, this is on CNC zone. That must be worth a look.

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Originally Posted by Ross77

Wow thanks guys, thats a great help, now if i could just get someone to convert the schematic to a pcb and mill it for me.....

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I can do the conversion of the schematic - I've done a fair number of PCBs myself (using Eagle PCB). Just send me the schematic, an idea as to what size you want (and also any heatsinks - most of the stuff I do is low-current digital, although the fan control was high current).

However, milling it... I photo-etch them myself, since I have the capability.

http://www.tribbeck.com/electronics/pcbs/

If you're interested :smile:

If you want to do it yourself, then there are a few rules to follow - graffian's advice is sound, but Eagle does have a "DRC" (Design Rule Check) which makes sure you don't break common ones (such as tracks too small, crossing over, pads too small, objects too close together). If you run this every so often as you're designing it, then it'll help you get along.

The photo-etching I do performs better than Eagle's built-in rules, so I've modified my rules to allow me to etch to within very tight tolerances.

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Originally Posted by Ross77

Tribbles
Thanks for the very kind offer, Unfortunatly I have no idea where to start with the code. I can only guess that an output needs to modulate (or switch low) the vref line to set the hold current (possibly adjustable from a trim pot) and then an input needs to look for the clock pulse to reset full current when a signal is seen?

I would imagine that the timing's are going to be the hardest bit as it might loss the first step whilst switching back to full current?

Is there any reason why this couldnt be put on a separate board and just send the Vref lineto the driver board with the other signals?

Thanks again

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I actually meant discuss with Irving :smile:

Looking at his (later) reply with the rough idea of the code, that looks sane to me, and roughly how I'd go about it.

INT0 would be the interrupt from the INT pin; INT1 would be the Timer0/1 interrupt.

DIP switches for the timeout's a neat idea - especially if it'll be used by someone who doesn't have reprogramming capability.

I have a slight concerna about using the PWM - if the PWM controls the direction control (i.e. oscillates between output 0 and open-collector), then that would be fine. However, from memory, it'll only oscillate between 0 and 1, then you'd need to be careful of the PWM pulse width - you could end up going too high with the VREF signal. Still doable though.

There's nothing stopping you from putting it on a separate board.

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Originally Posted by tribbles

....
I have a slight concerna about using the PWM - if the PWM controls the direction control (i.e. oscillates between output 0 and open-collector), then that would be fine. However, from memory, it'll only oscillate between 0 and 1, then you'd need to be careful of the PWM pulse width - you could end up going too high with the VREF signal. Still doable though.

There's nothing stopping you from putting it on a separate board.

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Depends on the chip and whether an O/C output is available. If not, a single NPN small signal transistor and base resistor on the output would suffice.

Having said that, if you are using a transistor, why not put a trimmer on the output side and not use PWM at all... would simplify the code and you could adjust the holding current to your hearts content.

Thanks graffian, I think I was about to make that mistake. I'll have to look for that thread, will it still apply to the L297?

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I can do the conversion of the schematic

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I will definatly take you up on that offer, If you make the board bigger than 4"x3" will i be able to veiw and output it myself? Good info on the PCB fabrication but think it will be too costly for a one off, as i plan to mill future pcbs.

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I actually meant discuss with Irving :smile:

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You've got me sussed, I'll go and sit in the corner then.:heehee:

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a single NPN small signal transistor and base resistor on the output would suffice.

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Wouldnt this then be the same as using a 555?

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Originally Posted by Ross77

Thanks graffian, I think I was about to make that mistake. I'll have to look for that thread, will it still apply to the L297?

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From what I remember, Mariss had just noticed the A3986 thread and it started with a comment he could programme a CPLD, pretty much as the gecko stepper drives minus mid band resonance, to do what the A3986 was meant to do. Then another post suggested he would be able to sell them for $5! I imagine you would drive bridge drivers[ir2184?] from the cpld?

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Originally Posted by Ross77

I will definatly take you up on that offer, If you make the board bigger than 4"x3" will i be able to veiw and output it myself? Good info on the PCB fabrication but think it will be too costly for a one off, as i plan to mill future pcbs.

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I'll try to fit into 100x80mm (this is the maximum size for the free version). However, I think you would be able to load the larger size in, but you probably won't be able to move the components that are outside the area around.

There are techniques to squeeze it into a smaller space, but I'll avoid them (basically, moving to surface mount components) unless you've got a particular desire to solder really small components :wink:

Send me a PM (let me know when you've done it - I think the last one didn't arrive), and I'll give you the details. I can have a rough idea as to whether it'll fit or not probably in an hour or so.

The point of the pic is an alternitive clock, the data sheet stats "that if more than L297 is connected then the clocks should be connected to syncronise the circuit", just to the right of the pic is a change over jumper one side grounds pin OSC on the L297 the other wires in the RC oscilliator components 22k and 3n3F. the pin of the pic which is wired to the (top) of v ref pot is a pullup and will have no effect in modulating Vref or anything else
Roger

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Originally Posted by cncezee

The point of the pic is an alternitive clock, the data sheet stats "that if more than L297 is connected then the clocks should be connected to syncronise the circuit", just to the right of the pic is a change over jumper one side grounds pin OSC on the L297 the other wires in the RC oscilliator components 22k and 3n3F. the pin of the pic which is wired to the (top) of v ref pot is a pullup and will have no effect in modulating Vref or anything else
Roger

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Roger,

Not sure if you are looking at the same diagram we are, but the PIC very definitely does connect to Vref - the 3.9k resistor and 1k pot are a potential divider to make the max value of Vref = 1v (blue wiring). The PIC clearly has the ability to ground the top of the pot which will drop Vref to about 20% approx (assuming the PIC output is 0.2v) of its set value.

The OSC circuit (red wiring) does indeed have a jumper on it, but thats to enable an external oscillator input for the reasons you suggest, and has no relationship to the PIC or Vref circuit.

Hi Roger, I think I know what you are refering to as I have seen cuircuits that use a Pic for the clock frequency, but this circuit definetly uses the Pic to change the Vref. :smile:

Ok so no luck finding the code for the pic, plently of references to its theoretical use but no specifics. There are plenty using the 555 timer circuits tho.

The closest I can find is the Rotary table drive that kwackers posted. apparently it was designed to drive an L297 setup and provide a holding current using PWM on the Vref pin. The only problem is I cant open the hex and wouldnt know what to look for any way. Maybe I will have to ask him direct for help :whistling:.

Ive also found conformation that this circuit was never built or tested so Im inclined to leave out the Short-circuit protection for the motor wires to keep it simple. may be I could look at it later and just use a known design to get the mill working?

Progress so far is three options.

1. Basic . as per data sheet but with half step boost and ne555 controling the idle current reduction
2.Ideal. as basic but with PIC controlling the idle current reduction and shunt reg to stop over voltage (not sure if I need to include the mosfet from the original as well?)
3. Complete. as above but with output short-circuit protection. (not sure about that now as it is quite different fron the data sheet! posted earlier)

Any thoughts, omissions or additions?

There is an error with the Vref circuitry with the 555... Vref should be connected to the slider of the pot...

Cheers thats the advantage of a fresh pair of eyes :smile: I thought I'd fixed most of the errors.

Any thoughts on using the short circuit protection and if i need the mosfet in the shunt regulator?

I've only had a quick look at this thread and the circuit, but imo the pic is simply controlling VRef. It's possible it is modulating it to provide variable VRef - but I think this unlikely since there's not a lot of point with the voltage divider if that's the case.

What I've done in the past to control a 297 is run the output of the PWM through a two stage RC filter to set the current, but doing this means there is no need for anything else around the VRef pin.

I think if I were working on that circuit I'd consider replacing the 297 with the PIC (albeit a slightly fatter pic). I'd use one of the comparators along with the PWM brought out as above (other side fed via the the current sensing resistor as per normal). Think I'd probably do most of the work in the interrupt probably using change on port ints to detect comparator and clock change. Should be possible to include microstepping etc - along with the current control stuff.

Failing that, why try and match exactly the circuit? Do as others above have suggested and simply use a 555 as a charge pump to keep the motor in high power mode.
All you really have is two supplies to your VRef pin - one permanently at 5v the other switching 0 to 5v. Run them both through a resistor (possibly the 555 output through a diode to make it easier to figure) and to the potential divider. If the resistor values are matched then roughly speaking when both are on the current will be double that when only one is on. Obviously you can chose resister values that give you the ratio's you're after.

Hope that makes sense.


[edit] I see above there's a circuit using the 555 ;-)

AAhhgg, more options. Thanks for your input tho. I like the idea of replacing the L297 with a pic as this is apparently the main cause of the buzzing. but way beyond my capabilities at the mo.

Ive been looking at the follow up thread to the A3986 debate (big can of worms) and it seems that PWM is better than the chopper control of the L297. However there was also a comment on a similar theme that suggested that the L6203 isnt the best choice for the h bridge either :rolleyes:

Looks like I'm going round in circles.

Steve
I believe the pic is lowering vref only when the step signal stops. In normal use the trim pot is setting the Vref.I agree that the 555 option is the easiest but the pic option uses less components so helping with a smaller board and slightly reduced costs.

Thanks again