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

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.