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

[borntofight00]

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

[Doddy]

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.

[borntofight00]

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?

[Doddy]

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.

[Doddy]

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).



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.



All other outputs and inputs tested okay.

[borntofight00]

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 :)

[Doddy]

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.