Laser firing from button, but not from PC?

[j_siegel]

Hi all,

I posted about this problem a bit back in my build log (http://www.buildlog.net/forum/viewtopic ... 6&start=30), but seeing as I'm still having trouble, I thought this might be a more appropriate place to post.

The summary of the problem is that I can get my laser to fire from the red button, but not from the PC. I used to be able to get it to fire from the PC, but then after moving I lost that capability. I beeped everything out according to the schematic and it was fine and continuous where it should be. I noticed that the voltage was not quite at 5V, so I ordered an output buffer board from CNC4PC (C26) to boost my signals to 5V. I also ordered another PCI parallel port (good to have on hand anyway), but have not yet installed it.

I'm at a loss as to what to try next. I don't know why it would fire from the front button but not the parallel input if my laser appears to be wired according to the schematic (of course, there are always things we miss). What should the next step be for troubleshooting? I will try replacing the PCI card tomorrow, but I feel like there's something I'm missing inside my electronics assembly.

Thanks in advance for all the suggestions!

-Josh

[mxk]

If you cannot find it in the hardware then you should look elsewhere. Did you by chance have separate running and saved configs before you moved? Maybe sending different commands or using different pin assignments?

[j_siegel]

I did upgrade from WinXP to Win7. I thought I moved the config file, but I did change from Digital Trigger (for the Engrave plugin) to Output #1 (for E1P1 control). Perhaps I messed something up in the config, but I am still getting a digital high signal on pin 17 all the way to the laser power supply. I will review my config further, as it does seem like it should be firing. Maybe it's in the power supply.

[bdring]

Is the water pin connected to ground? Try shorting it directly to ground. If you check with a meter do it using the Ohm meter and not the beeper. Sometimes the circuitry can fool the beeper into a little beep.

[j_siegel]

Water circuit works fine, it's direct to ground. The whole circuit has ~4 ohms of resistance, which should be fine. There is no potential between GND and WC.

Here's how things beep out:
TH: 5V (no signal) or 0V (active low checked).
TL: 5V (button open) or 0V (button pressed).
WP: 0V.
GND: 0V.
IN: 0-5V, pot dependent.
5V: 5V.

That seems exactly like how it should be. Unless I am mistaken, this points to a faulty PSU. I will contact lovehappyshopping and see what they say.

[BenJackson]

You seem to have TH wired backwards. The laser will fire if TL is pulled low OR if TH is pulled high. If you have it wired with TH high all the time, perhaps the laser PSU has a safety that prevents it from firing if the signal is high on power up. TH is definitely not "active low".

[j_siegel]

Hi Ben,

Thanks for the reply - but I think maybe I wasn't clear enough (alternatively, I might have misunderstood your reply - if so, please forgive me).

The logic on TH can go either way (0/1 or 1/0), depending on whether or not "active low" is checked. I also understand that it is supposed to be "active high," and it sits at 0V until it's ready to fire (when the trigger bumps it to 5V). I was simply noting that changing the setting in Mach 3 to active low did, in fact, flip the voltage - so it can't be the PCI card. It can bring that pin high or low, all the way from the PC to the PSU.

When I first boot the PC, pin 17 is sitting at 5 volts. Is it possible that there is some initialization routine, or power-on order, or something else, that the power supply wants to see before it can be triggered appropriately? Start the PC, open Mach 3, then turn it on? Some other black magic? I've tried just about everything. I'm fairly confident that the power supply is to blame here - but I have been wrong before.

[j_siegel]

It's been verified as a bad PSU. Applying 5V direct to TH, and I still get nothing!

I am waiting on the seller for a reply, but I imagine that being about 90 days out, I'm SOL. Perhaps an AND gate joining the push button and the trigger line (set to active low) would work, rather than having to replace the whole supply? I'm a bit wary of looking inside the HV unit to see what's busted.

[BenJackson]

If it's really that simple I'd ohm out the trace from the TH line to the control module. It may just be a cracked trace or bad solder joint (or even failure of the screw terminal plug to mate with the socket).

If you want to fix it externally I wouldn't modify the button. The laser fires for TL or TH, so you would just need an simple logic circuit to take one active high input (or since you control the PC, you could make it active low) and OR it with the active low input TL and produce active low output TL:

Code: Select all

    | TH  |
    | 0 1 |
----+------
T 0 | 0 0
L 1 | 1 0


One 74HC logic chip powered by the 5V from the PSU could handle it. You pick something like a 74HC02 quad NOR and use one of the NORs (with inputs tied together) as an inverter. If you need help I can draw the whole circuit.

[j_siegel]

It really was that simple! I opened up the case for the PSU and the wire had come disconnected on the PC board side of things. I reconnected it, and now, it fires just fine!

Ben - Thank you so much for your encouragement and help figuring this out!