T2 laser comes on when going to laser control. SOLVED!!

[a_kent]

When going from the main editing screen to the laser control screen, the laser comes on full for a couple of seconds.

This is startling and puts a mark on the board. I also am not in the habit of putting on the goggles until I hit 'go'!

I am running the A5 2500mw Banggood machine with the Mana SE board, with 1.1E firmware and T2 version 1.3W registered.
I have had it running only for a couple of days.

Is there a way to stop the laser from coming on like this?

Regards,
Kent

[nottingham82]

oh the dreaded ttl firing up.  So this is a known issue.  Carolynsdad found a way to cut the circuit.  He has a writeup on it and Zax is working on something.  It has to do with the nano firing up during the pc handshake. 

[Zax]

It happens when Grbl is starting up, or rather before it has started. It doesn't do it on my system so must be a design fault with their latest modules.

There's not really a firmware/software solution although I may be able to workaround it.

Just leave the controller off until you are in the laser screen.

[a_kent]

I would be very interested in seeing what Carolynsdad found out!

I'm also a retired EE, so I can do things.

I do have the GRBL source tree. I have not scrounged for schematics on this design, although I seem to remember that it's all public domain.

Thanks!
Kent

[Zax]

Are you in the USA, and is you're laser what came in the latest kit?

Feel free to PM or email me if you prefer.

[a_kent]

Yes and yes.

[ggallant571]

The design is not public. I reverse engineered the L7 & L8 controllers and posted the schematics on this site.

It is somewhat odd that not all systems behave this way. The the signal used for laser ON/OFF control is floating during reset but should not provide sufficient energy to turn the laser on. I suspect a pulldown resistor might might help. It is also possible that the boot firmware on some boards is driving the signal high.

IMO, the solution is to add hardware with an ENABLE signal (with pulldown) from a completely unused I/O pin.
 

[a_kent]

The design is not public. I reverse engineered the L7 & L8 controllers and posted the schematics on this site.

It is somewhat odd that not all systems behave this way. The the signal used for laser ON/OFF control is floating during reset but should not provide sufficient energy to turn the laser on. I suspect a pulldown resistor might might help. It is also possible that the boot firmware on some boards is driving the signal high.

IMO, the solution is to add hardware with an ENABLE signal (with pulldown) from a completely unused I/O pin.
 

Hi GG:
That is great that you were able to reverse engineer those things.

NO SIGNAL should ever ever be left floating!!! Rule in my camp. To many things can happen to that signal. All bad.

I have seen signals left floating where a new silicon revision caused a state change at any given point!

While I have no clue yet why this signal is doing what it is, I hope to find out.

I do know from past Atmel designs that you can program pull ups and pull downs in the firmware fuses. I think this is an Atmel processor used here, so yes, you can affect the hardware with the boot code and firmware, possibly.

Kent

[Zax]

The problem happens before Grbl is running, as it's booting up.

The pins haven't been assigned as inputs or outputs so are floating or in the wrong state, of course a good electrical design on the laser module side would still not allow a floating input to turn on the laser, even adding an enable pin wouldn't help if they don't design it correctly (it may also float high and trigger the laser).

I am going to send a_kent a Nano running Grbl 1.1e without the boot loader. It starts up almost instantly which I am hoping may help this situation. If you remember from Hippie's thread I wasn't able to replicate the pulse or see it with my o-scope but it's still worth testing.

[a_kent]

Well, it's fixed!
It really is the simple issue of a floating signal. I also consider this an engineering oversight.

If any of you have a Mana SE, you can easily see if you have this issue.
Put your glasses on first!!
Turn off the power to the board.
Unplug the USB cable from the Nano.
Then turn on the power to the board with the 12v supply plugged in.

On mine, the laser would go to full on and would stay there.

Mine would also turn on the laser when you first turn on your computer if you turn on the machine first. It would also turn on when you go into laser control mode from the T2 software.

To fix this, I installed a 1k ohm pull down onto the laser signal on the large board.
(Solder a 1k ohm resister between the 'S' signal and the center ground signal on the laser connector.)

Any resister value >1k is not enough.

On mine, this left the float at about 0.4 volts. When it is floating after power on, there is a very low level light from the laser, about like pressing the button on the laser module.

Also if anyone is using this board for driving a motor on the red connector, this same signal goes to the gate of a Mosfet that controls that motor. It will come on the same way the laser does without this pull down.

Best!
Kent

[a_kent]

And a HUGE thank you to Zax for the offer of sending a Nano board to me!!

[pascalp]

I've just solder a 1k ohm resistor. Seems to works, test in progress.
Thanks

[ggallant571]

@a-kent - I consider it more than an engineering oversight. The entire MOSFET drive circuit is deficient. Each MOSFET has has definitive current and voltage requirements to reliably turn fully ON/OFF in a specified time. The AVR328 I/O pin barely suffices. I have 2 cheap NANO clone boards that generate less than 4.2V for a logic high and they cannot fully turn the MOSFET ON. The result is excessive heat. Eventually (2 minutes) they get stuck in the ON state and melt the PCB trace.

I have posted before and some users say my analysis is wrong. I contacted the MOSFET manufacturer and they agree with me. My boards now contain dedicated MOSFET driver chips. They work reliably and run cool with 3.3V ARM processors.

Perhaps there are power MOSFETs that do work with 5V logic. IMO - This circuit is something that a legitimate engineering department would investigate and make rock solid before releasing onto the consumer market.

[jtice]

Any pics of where exactly you are soldering the resistor on?
Mine does as described, I have learned to just NOT have the work piece under the laser until AFTER I have started laser control.
But it would be nice to actually fix it.

[pascalp]

My modded Mana SE, limit switch on D9 and 1k Ohm resistor.