CNC plotter 1800 x 80cm, first build, questions and queries.

This is my first forum post so first of all, hello everyone! I am at the stage of building the first cnc plotter, quite large and heavy as for the first machine (about 1.8m x 0.8m) and I would be very grateful if you could help me with electronics. Quite a long time ago I inherited second-hand electronics, theoretically complete set, after amateur coversion of a mini milling machine, although I have problems with it and I hope that this is my lack of knowledge. I would love to use as many components already bought as possible .. but to the point:

Breakout board - CNC4PC model C1

1. The motors do not spin despite the fact that Mach software shows movement using the arrows on the keyboard. The motor is locked, it cannot be turned. There are diodes on the breakout board, it seems to me dedicated to outputs, not activated, only the 'outputs status' diode is on, what should I check step by step to verify if the board is ok?

2. How to check if the drivers are ok? The voltage is fine, 42V on each of them. The voltage between A + and A- and B + and B- in the case of one motor connected is 1.7V, in the other 1.4V. Where there is no motor connected, 42V between A + and A-. Is this correct?

I would have more questions, but for now, the most important is to verify whether the board and drivers are in full working order and configured with Mach3. The attached photos show Mach3 settings, previously configured with current set up. Thanks in advance for your help, I will post a full 3D project and a schematic after completing the project here. I’ll post more details about my design soon.

Regards!

It's been a while since I used one of these but I seem to remember they needed a 5v supply for the charge pump or a jumper setting on the board to disable it. So check the board and there will be 3pins together if I remember correctly with 5V and EN and Gnd. Put a jumper across 5V & EN pins if there isn't one there already and it will disable the charge pump.
If the board doesn't see 5V across these pins it will disable the outputs which is probably why it's not moving.

Or you can just put 5v+ on the EN pin and it keeps the charge pump in place then if you lose 5v the outputs get shutdown. Your choice.

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Originally Posted by borntofight00

1. The motors do not spin despite the fact that Mach software shows movement using the arrows on the keyboard. The motor is locked, it cannot be turned. There are diodes on the breakout board, it seems to me dedicated to outputs, not activated, only the 'outputs status' diode is on, what should I check step by step to verify if the board is ok?

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Mach 3 doesn't get any feed back from the motors so it just assumes they are moving that's why the Dro's show movement. The BOB as probably disabled the outputs as per my other post.

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Originally Posted by borntofight00

2. How to check if the drivers are ok? The voltage is fine, 42V on each of them. The voltage between A + and A- and B + and B- in the case of one motor connected is 1.7V, in the other 1.4V. Where there is no motor connected, 42V between A + and A-. Is this correct?

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Be very carefull when you are sticking probes into this area you can very easily fry those drives and what ever you do, DO NOT disconnect the motor connections from the drives while powered up or you will 99% destroy them. It's perfectly fine to power the drives without the motors attached but never remove the motor wires while drives are powered up.

Simplest test first is as Jazz says - check the BOB EN pin and that your e-stop isn't activated. Been there... worn the tee-shirt.

To test the drivers, disconnect the PUL+ wire from the break-out board to each of the drivers one at a time, and with a bit of wire in the PUL+ input to the driver strike that against the +5V supply. Each connection (and each break/make as you make the connection) should turn the respective motor by one step (or microstep). You might get more joy just listening if the drivers are configured with a large number of micro steps. That will give you a basic level of confidence that the drivers and motors are okay. It's hard to predict the terminal voltage of the drivers - depending upon the motor position you're going to see an instantaneous (static) description somewhere along the waveform of a sine-wave across A-/+ and B-/+ each 90 degrees out of phase (so when A is +Big Volts, B would be tending to Little Volts.... but all depends on where the driver thinks it is along it's rotation.

You could also strike +5/0V across the EN+/EN- of each driver. That should free the motor on that axis. Not very useful, but again some confidence in the operation of the driver.

If you get that far then your issues lie either in the break-out board, or your Mach3 installation.

It worries me that you say that none of the LED outputs are illuminated - if you jog one axis in one direction, then the other, at least one of the LEDs for the DIR outputs to the drivers should be illuminated in one jog direction. Failure of this would be an indication that there's a problem or misconfiguration of the BoB. Or the EN input. Or the connection to the PC.

Thanks very much for the instructions, as you pointed, motor rotates at each 5V strike, in addition, 5V connected to EN + free the motor so that’s the good news I believe.

This is my first contact with stepper motors so please be patient  When striking 5V, sometimes the motor's rotation is ‘uneven’, i.e. it’s jumping one step but sometimes it feels like it’s jumping a few steps and sometimes one step in opposite direction. I guess, this is due to not precise pulsing by using simple push button? I’ve connected n/o push button between 5V source and PUL+ btw..

Also, with e-stop off:

I can measure 5V between 5V & GND and between EN & GND terminals. LED called 'output status' is illuminated.

With e-stop on however:

5V between 5V & EN and 5V & GND terminals. 'Output status' LED is not illuminated.

What do you guys think?

The semi-random effect is as I'd expect. Even using a N/O push button rather than just a bit of wire you're going to get something called "contact bounce" where pressing the button generates a whole bunch of On/Off transitions as the button contacts literally bounce against each other. This usually dissipates within a few milliseconds, but you can certainly get more than one "contact" per press and with a fast stepper setup (usually rated into the hundreds of kilohertz - sub 10 microsecond territory) you might expect a fairly random number of pulses / rotational steps. But, they should be in one direction only.

I'm going to largely ignore your voltage measurements - because I don't understand quite what you've written. I *think* you're saying with E-Stop off you confirm you have 5V (all measurements taken with the meter's black lead connected to 0v) supply to the BOB, and 5V on the EN enable pin, and the LED 'output status' is illuminated, and with the E-Stop on you confirm the EN enable pin falls to 0V and the 'output status' is not illuminated? That's what I'd expect to happen and is again a good thing. It indicates that you have power to the board and your e-stop circuit is operable.

My concern now lies with no sign of life from the LED indicators on the outputs from the BoB. With the-estop OFF : Using the cursor keys to pseudo-move the X-axis in one direction or another you will be changing the X-DIR signal between 0v and 5V (can't tell you which way around) - which should illuminate/extinguish the LED on output pin (3) on the BoB. I'd use that as your primary sign-of-life from now on.

So, your stepper drivers are showing signs of life, together with your motors, so I think it's time to concentrate on the board and the Mach 3 interface to this.

1) My first question is - has you witnessed the actual computer that you're using with Mach3 successfully drive this board?, I think from your description - no? The problem here is chasing a potential ghost - if the PC is not set-up correctly then you can probe the board all you like and there'll still be no life.

2) Are you using a full 25w wired parallel cable between the computer and the BoB?, have you tried a quick continuity check to make sure pin-1 goes to pin-1 etc through pin-25? (if you found a random 25w cable it *could* be a serial cable with only a small number of wires connected, and some of those possibly swapped). Check the basics.

3) Of interest - on the BoB - there's a 3-pin jumper header labelled "JP1" - there should be a shorting pin connecting two of the pins together - which two?

4) Would you be confident to ***CAREFULLY*** measure the voltage on pin-1 of the 25-W D-type that the computer plugs into, with the system powered. I'm talking about connecting the meter black lead to 0V and carefully probing the PCB where the pin-3 is, and measuring the voltage with the X-Axis moved in one direction, then again with the X-Axis moved in the opposite direction. In one direction you're expecting a voltage less than perhaps 0.8V and in the other direction greater than perhaps 2.5V.

5) Much easier - could you do this again on the PC. insert a couple of pins or bits of stripped solid strand wire (paperclip?) into pin 3 and pin 25 of the PC parallel port and measure for each direction of X-axis travel. If you can provide a photo of this for our amusement (and validation) - this is getting to the point where we should be able to understand the PC->BoB communication - I think the BoB's basically functional, so this is important to understand why the BoB is not seeing the commands from the PC.

So far so good!

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Originally Posted by Doddy

I'm going to largely ignore your voltage measurements - because I don't understand quite what you've written...

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Bad wording, sorry. Anyway, you are correct.

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Originally Posted by Doddy

1) My first question is - has you witnessed the actual computer that you're using with Mach3 successfully drive this board? ..

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No, unfortunately I wasn't able to see everything working. I was given two PC's during system collection with the information that one of them was used with this equipment and should still be ok.

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Originally Posted by Doddy

2) Are you using a full 25w wired parallel cable between the computer and the BoB?..

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I'm using brand new 25w parallel cable and I tested each pin for continuity, all fine.

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Originally Posted by Doddy

3) Of interest - on the BoB - there's a 3-pin jumper header labelled "JP1" - there should be a shorting pin connecting two of the pins together - which two?

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This shorting pin is connecting pins 2 & 3 (COM=GND)

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Originally Posted by Doddy

4) Would you be confident to ***CAREFULLY*** measure the voltage on pin-1 of the 25-W D-type that the computer plugs into, with the system powered. I'm talking about connecting the meter black lead to 0V and carefully probing the PCB where the pin-3 is, and measuring the voltage with the X-Axis moved in one direction, then again with the X-Axis moved in the opposite direction. In one direction you're expecting a voltage less than perhaps 0.8V and in the other direction greater than perhaps 2.5V.

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I managed to measure a voltage for X, Y and Z axis (just in case) and I was getting just a little bit above 2.5V and 0.07V (not too low?)

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Originally Posted by Doddy

5) Much easier - could you do this again on the PC. insert a couple of pins or bits of stripped solid strand wire (paperclip?) into pin 3 and pin 25 of the PC parallel port and measure for each direction of X-axis travel. If you can provide a photo of this for our amusement (and validation) - this is getting to the point where we should be able to understand the PC->BoB communication - I think the BoB's basically functional, so this is important to understand why the BoB is not seeing the commands from the PC.

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Take a look at the pictures attached, for your amusement :) I’m measuring 3.35V & 0.036V, almost identical on pins 3 to 9.

From what I understand, there is a communication between PC and BOB, but there is no signal to the outputs .. as you can see at the picture, BOB is a little bit messy so would it be a good idea to give it a good clean with isopropanol for example?

Another thing that I have spotted is LED next to PC power terminals which was illuminating for some time while PC was running but the rest of the system wasn’t powered. At some point, it disappeared .. is it normal?

I really appreciate the time you spend pointing me in the right direction.

Attachment 27904Attachment 27905Attachment 27906

Any chance to help me take few more steps forward guys?

Sorry, I lost track of this message reply, and back at work today so slow to respond.

This board confuses me a little - there are two 5V supplies indicated to this, yet no specific mention in the manual about how to wire these. More interesting is figure 1 in the pdf (https://www.cnc4pc.com/pub/media/pro...SER_MANUAL.pdf) which shows that the PC parallel interface is isolated from the output drive system. This implies pretty strongly two PSUs.

I asked about measuring the parallel port for two reasons - that Mach3 is driving it properly (generally is, at least the DIR signals) and that it is set to TTL levels - it isn't - it's driving 3.3V which is not ideal, but the image for the chips on the board - ACTs should tolerate this at a logic level. You cannot scavenge 5V directly from this parallel port so with reference to figure 1 I'm wondering how the PC-side interface on the board is powered, versus the "output" side of the board. There is information within figure 1 to suggest "PC +5V" and "PC 0V" which are the two terminals at the top of the board, which in your photo are unconnected.

So, if you will endure me, I'd ask if you can measure the voltage at the PC +5V to PC 0V at the top of the board as shown in the photo. If there is NO measured voltage then I'd ask you to wire the +5V to the main +5V supply, and the 0V to the main 0V. This destroys the galvanic isolation between PC interface and output drivers, but it's a quick and easy test.

Thanks Doddy!

Following your instructions, here's what I found: with the PC turned off, the moment I turned on the system, the LED next to the 'PC Power' terminals came on and the voltage between them was 1.8V. When I turned on the computer, the LED went out and the voltage also disappeared. I remember that a similar situation has happened more than once before and I could not figure out at what point LED was disappearing, now I know. I turned off the computer, turned off the system, waited a few minutes, turned on the system again - PC LED was no longer on, no voltage as well. I repeated the process again, this time I waited longer, the result was same, no voltage, no LED.
Then I wired +5V & 0V. At the time of connecting the LED output diodes ‘blinked’ sending a few short pulses (without the use of software) to the motor but the 'outputs status' LED disappeared, which is not desirable I’m guessing? So now, with 5V wired to PC Power terminals ‘output status’ LED is permanently off.

With such behaviour, do you think that it might be a time to think about the new BOB or perhaps something more to check?

Just re-reading the pdf, "That is the reason why this card has two power connections. One power connection is power powering the circuit that interacts with the PC, the other connection is for powering the circuit that interacts with your CNC system." - that confirms my assumption that the two power-supplies need to be provided (and I'll say without reservation that they can share the same PSU source - the only reference to the PC are the ground pins on the parallel interface which will be commoned with the 0V on the PC supply on the board). So I'm happy with the PSU wiring I proposed.

It's interesting that without that wiring the board scavenges the low-level supply voltage (1.8V as you measure) - it's unclear to me exactly where that's sourced from - wouldn't have thought from a powered-off PC, but it's if the two halves of the board ("PC" and "Output") are galvanically isolated as the pdf suggests then there's little other option. It is in part explained with the turning-the-pc-on-extinguishes, as the PC boots if it is resetting the parallel port signalling - clearly something on powering the PC changes something that drives the LED on the board, and similarly leaving the PC powered off extinguishes the LED eventually - so perhaps there is some residual supply on the parallel port when "off". An interesting observation, nothing more.

So, you wired the supply and the outputs pulsed and the output LEDs blinked?, so you've probably now bridged the PC-side signalling to the output-side drive, that's triggered the outputs, but the output status is now inhibited. Okay, that supports the PC supply theory, now the question is what has the board done to determine to inhibit the output

If you have +5V on the PC +5V and the main board +5V and also on the EN input - then the board should, from what I've read, operate. Dean (JazzCNC) refers to a charge-pump - from what I understand the charge-pump is implemented separately off board and signalled through the EN input (which corroborates the advice to pull this high) - so I don't see any other required signalling to operate the board (the linked PDFs in the manual (http://cnc4pc.com/Tech_Docs/E_STOP_N_SCHP.pdf) suggest throwing a charge-pump output from the PC onto output pin 17 - but without an external charge-pump circuit this should not be necessary.

At this stage, given the above measured voltages (PC+5V, +5V, EN) I expect the board to function. You ask whether it's time to think of a new BOB?, your call - you can pick them up for very little cost, or pay rather more for something as robust as this C1 board and test by substitution. Clearly from my perspective the board function as described is at odds with what I expect, but I might be missing a trick here (to be honest, there's not a lot to get wrong with a BoB, so I'd be surprised). My instinct is that the board is at some level functional - I'll offer to test the board for you to a level that I can diagnose the behaviour of each major functional block - but I don't know how that sits with your time-frame - it might be quicker just to get a BoB ordered in the post).

The only other minor concern I have is the 3V3 operation of the parallel port. The "old" 5V interface is normally enabled by configuring the parallel port to EPP mode in the computer's BIOS, but in the absence of any charge-pump circuit this doesn't explain the inhibiting of the outputs, and as stated earlier the 74ACT's should operate sufficiently well with 3.3V logic. So I'm not going to dwell too much on that.

on the photo of the breakout board. If you look at the 8 pin chip to the right of the 25 pin connector in the bottom left corner. It doesn't look to be seated in its socket correctly. Should just push in to seat fully. Quite common for chips to work out of sockets over a period of time.

Hi and big apologies for not coming back earlier, however I had to do urgent house maintenance job which took me the last few days!

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Originally Posted by mnewsholme

on the photo of the breakout board. If you look at the 8 pin chip to the right of the 25 pin connector in the bottom left corner. It doesn't look to be seated in its socket correctly. Should just push in to seat fully. Quite common for chips to work out of sockets over a period of time.

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I’ve spotted this straight after my first post and pushed in back into its place, thanks!

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Originally Posted by Doddy

So, you wired the supply and the outputs pulsed and the output LEDs blinked?

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Well, I should explain a little bit better .. they are blinking when touching +5V terminal as same as previously supplying 5V to stepper motors. Once hardwired, all output LEDs are off.

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Originally Posted by Doddy

My instinct is that the board is at some level functional - I'll offer to test the board for you to a level that I can diagnose the behaviour of each major functional block - but I don't know how that sits with your time-frame - it might be quicker just to get a BoB ordered in the post).

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Doddy, if you have some spare time and willingness to help, I would appreciate! I don’t really have any deadlines, just trying to make some regular progress but please if at any point you will think that something is not right with Bob, let me know and I’ll get a new one as instead of wasting your time on this, I could ask some other questions. Is it worth investing in this type BoB or are there better options in let’s say £100 budget?

In a meantime I’ve sent an email to CNC4PC asking them for some more information about wiring and below is what I received:

‘this is an isolated board, so it has two power terminals. Make sure you are using both. The side that interacts with the PC can be powered with a USB cable. Make sure you put a jumper across the EN and the +5vdc next to it.’

Still don’t explain why all the outputs are inhibited when 5V is wired to PC power terminals. What do you think??

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Originally Posted by borntofight00

Hi and big apologies for not coming back earlier, however I had to do urgent house maintenance job which took me the last few days!

I’ve spotted this straight after my first post and pushed in back into its place, thanks!

Well, I should explain a little bit better .. they are blinking when touching +5V terminal as same as previously supplying 5V to stepper motors. Once hardwired, all output LEDs are off.

Doddy, if you have some spare time and willingness to help, I would appreciate! I don’t really have any deadlines, just trying to make some regular progress but please if at any point you will think that something is not right with Bob, let me know and I’ll get a new one as instead of wasting your time on this, I could ask some other questions. Is it worth investing in this type BoB or are there better options in let’s say £100 budget?

In a meantime I’ve sent an email to CNC4PC asking them for some more information about wiring and below is what I received:

‘this is an isolated board, so it has two power terminals. Make sure you are using both. The side that interacts with the PC can be powered with a USB cable. Make sure you put a jumper across the EN and the +5vdc next to it.’

Still don’t explain why all the outputs are inhibited when 5V is wired to PC power terminals. What do you think??

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Happily take a look for you - will PM address - if you find a solution in the meantime that's good.

The response from CNC4PC corroborates the info offered earlier - that all makes sense. Their suggestion of using the PC USB is notionally to maintain the isolation on the BoB - that requires that the PC supply is isolated from the CNC Supply - by no means guaranteed. But doesn't affect the price of fish for this exercise.

The inhibited outputs when wired to the PC power terminals - that's the bit I don't understand and prime for investigation - at this point you've done all according to the book.

Question of BoBs - I like the look of this one - it's a well thought out design, however, I tend to go cheap (£5 BoBs) - if I can understand the interfacing to it (e.g. hooking onto an UC300ETH then I have NO qualms of a £5 BoB.).. whereas parallel connection to a PC I can appreciate the rugged nature of this BoB. Everyone else here will have their own opinion.

Okay, some weirdness now understood with this BoB.

The parallel port, pins 18 through 25 are supposed to all be grounded, at the PC side. A 25-way parallel cable should be expected to be fully wired, pin-1 to pin-1 through pin-25 to pin-25.

The "CNC4PC model C1" pulls the pin 18 high, and monitors this to be dragged low by the insertion of the parallel port cable to the PC. Without this, although the PC and the board supply voltage may be present, the outputs (at least) are inhibited.

Solution - a fully wired 25W parallel cable (and similarly wired parallel port), or short pin 18 to PC ground (pins 19-25).

Pic 1 - board with separate 5V supplies (PC and Main) - and EN set high. Power LEDs for the two supplies on, but the output-enable LED (on, if the main PSU is on, but extinguished with the PC power supply added). Shorting link from a ground to pin-1 to extinguish Output 1 LED (note: they are all off because pin 18 is floating).

Attachment 28134

Pic 2 - Added a ground to pin 18. Output-Enable LED is illuminated as are all other outputs, except for pin-1 because of the aforementioned shorting link.

Attachment 28135

All other outputs and inputs tested okay.

Hi all,

Huge thanks to 'Doddy' for fixing this issue, it is working now! It's time to make some progress, I'll update this thread within the next couple of weeks :)

Good to hear you're getting on.

In fairness, I've probably failed you - the postage and time taken - it'd have been quicker and cheaper to replace with a £5 BoB. But, I've learnt from this experience so for that I thank you.

Now go build your machine.