Laser issues - follow up and more info

Mostly Printed CNC - MPCNC Troubleshooting
1

Here is a video I took of the output signals from my RAMBo, hopefully helping with troubleshooting.

I still can’t seem to get the laser to turn off EXCEPT when I reversed the polarity of the TTL connection. However, doing that I can’t get the laser to turn on.

I seem to get the best signal using M42 P45 Sxxx

Using M3 Sxxx or M106 gives me a really dirty signal on the oscillascope for some reason.

Important details:
-12v laser with 5v TTL control (from China)
-Latest Marlin firmware from V1 (dual endstop)
-Channel 2 in the video is measuring between (-) on the MX2 rail and (-) on the power supply (ground)

2

That signal looks good. Do you get the same thing when comparing the ttl to the negative ttl?

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3

So the yellow signal in the video is measured between TTL (+) and TTL (-)

Should I be putting the ground on the scope to something different while measuring?

4

You said in the video and in your notes that it was measuring to the power supply ground. I am worried we are miscommunicating.

I am curious to see if any of the other voltages are goofy compared to this, because this looks fine.

5

Sorry, yep. I’m measuring 2 signals in the video.
-The yellow signal is measuring TTL (+) to TTL (-)
-The green signal is measuring TTL (-) to power supply (-)

I just wanted to make sure on the green signal that TTL (-) was actually connected to the power supply (+) which it appears to be.

Any clues as to why the laser wouldn’t turn off completely at S0? It’s definitely a lower power level but it still burns through cardboard.

6

It gets brighter at 5V, dimmer at 0V, but not off at 0V?

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7

Yes, exactly.

8

Ok. Looking at that video again. It looks like the ch1 isn’t really at 0V. Am I reading that right? Maybe a pull down resistor would help?

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9

Yes, it looks like it’s closer to 1v when S is set to 0 hey?

I’ll have to research how to add a pull down resistor. I’m an electrician, but this electronics stuff makes me scratch my head haha.

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10

If you have a resistor in the 1kOhm-10kOhm, you can connect it between the ttl(+) and gnd. It may be enough to “pull down” the voltage to ground when it is supposed to be off.

I am not sure why that is around 1V. If you disconnect the laser, and use your silly scope, does pin 45 stay around 1V still?

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11

I had the issue with laser on till arduino finished booting up the resistor did the trick

12

No luck with a 10K resistor, but the 1K did the trick. Thanks for all your help Jeff!

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