output discrete current

[paul_z]

What is the current limit that the output discrete can source? I might want to run a low power laser from one of the discretes. I'd rather not use/build a solid state relay if I can avoid it.

I have a PRT Alpha with the original controller.

Paul Z

[Brady Watson]

Real low...Somewhere between like 20-50mA. I would use a relay board anyway just to to get some isolation. Winford Engineering makes one that is cheap & works well.

-B

[paul_z]

I'll only need about 12ma so it should be fine.

I'd worry about isolation except the laser diode functions as a damping diode. Can't be any worse than the ZZero input going directly to the control board.

I'm mounting a crosshair laser near the spindle/router. It is adjustable + and - 5 degrees. Once adjusted to vertical in both planes, it should not need any further adjustments unless it is remounted or the router/spindle is adjusted. I’ll measure the offset between it and the center of cut and use that info to do an auto-offset by creating a “C” command. Not having to rechuck my current laser should save a lot of time.

Thanks Brady

Paul Z

[Brady Watson]

No problem, Paul. Post up when you get it set up.

-B

[jerry_stanek]

I'll only need about 12ma so it should be fine.

I'd worry about isolation except the laser diode functions as a damping diode. Can't be any worse than the ZZero input going directly to the control board.

I'm mounting a crosshair laser near the spindle/router. It is adjustable + and - 5 degrees. Once adjusted to vertical in both planes, it should not need any further adjustments unless it is remounted or the router/spindle is adjusted. I’ll measure the offset between it and the center of cut and use that info to do an auto-offset by creating a “C” command. Not having to rechuck my current laser should save a lot of time.

Thanks Brady

Paul Z


That is exactly what I did mounted my laser on my spindle and run a c offset command.

[paul_z]

The pics show the laser and it's mounting on my PRT Alpha.

I used a 6V battery pack with switch from Radio Shack and 4 rechargeable AA batteries. A 120 Ohm resistor in series with the laser drops the voltage to a safe level for the laser. If the laser were left on with freshly charged batteries, it should run for more than 6 days.

I paid less than $5 each for the lasers (several years ago). Unfortunately, the lens on the laser is where the crosshair pattern is generated. That means the crosshair rotates while focusing.

The lower screws on the holder keep the crosshair from rotating while adjusting the focus by rotating the laser body. The upper screws adjust the crosshair to be dead vertical as well as locking the focus.

I derived the x and y offset values by just touching the spoilboard with a v bit and then zeroing the x and y axis. Then I moved untill the crosshair was dead on the V peck on the spoil board. The offset is the negative of the current x,y position.

Next I wrote a 4 line "C" command.
Zero X and Y (Z2)
Move the offset (M2)
Zero X and Y (Z2)
End

To use the device, you turn on the laser, move the crosshair to your desired zero point, run the C(whatever you named it) command. The bot moves directly over the point the point that the crosshairs were on and zeros the x and y axis. Turn off the laser.

Random observations
1. The laser is far too bright. I think I'll add a 2K log variable resistor to dim it more. However, it has impressed everyone who has seen it so far. Maybe that is its true value???
2. It was easier to adjust than I thought it was going to be.
3. It does save time!
4. The laser mount and PRT Alpha adapter were made from baltic birch ply and cut on the bot (of course).
5. I'm guessing that the x,y zeroing is good to somewhere around 0.025". That's overkill for most of the work that I do.
6. The laser was positioned to be less in the x and y axis than the bit. This means that it can be used anywhere on the bed except for the extreme max x and max y. I don't care about that limitation because I can't see that far!

[Brady Watson]

Kewl! I'm diggin' the elegant mount. It works & it was cheap!

-B

[tomwillis]

Paul - looks great!
I'm not sure I understand why the need for the laser in the first place? Is it a question of repeatability?
Tom

[jerry_stanek]

I use mine for pre printed sintra they theow some register marks on it and I use the laser to hit the marks and register the material to my table. When they print they have a different zero corner so I have to hit 3 register marks to make sure it will cut out right.