5W Laser - Mini-Rambo - Assembly Pics

I’m not sure what you/they mean by TTL in this context. I thought that just meant 5V logic, and you’d still be using a PWM signal at 5V to determine the laser intensity. You would have the laser always powered, so you would get better control at low levels 5%.

So if the control board added a zener diode to dump voltage over 5V through a resistor, the 12V PWM would look just like a 5V PWM (which I think is the same as pin 44). To use the fan pin, you would also need a pull up resistor (because it really switches between open and ground).

Fan pin – Rup – 12V
|
| – 5V zener |< – ground.
TTL

The zener would dump any voltage over 5V to ground, which would have to come through Rup, which would limit it to something that would keep it all cool.

I wasn’t thinking this would be a separate board, I was thinking they should put the 2-3 more parts on the laser control board. I have no idea why that board has so much on it. There’s probably something I don’t understand about all this.

Yeah I have no idea why none of them have both voltages. You definitely understand this more than I do. I know at one point early on I tried a voltage divider and it did not work (I could have done it wrong).

I thought the drivers had some sort of power curve to them, to make the laser function smoother. Most let you set the output, some let you tune the startup/low point. Maybe that is all it is.

The D8,9,10 pins are either floating or ground, so you could do something like this:

12V – R1 – FAN/OUT – R2 – GND

I would try this with a scope first… I’m just spit balling here. I should probably test some of these crazy ideas myself.

When the FAN is floating, the output would be R2/(R1+R2)12V.
When fan is ground, it will be pulled down (so 0V), and the current it has to sink is 12V
12V/R1. So R1 of 7k and R2 of 5k would be about right (and only sinking 20mA when it’s on). A little bigger R1 would be on the safer side.

There’s probably something else that I’m oversimplifying. If you did something like this, it wouldn’t work:

FAN – R1 – OUT – R2 – GND

When fan was gnd, it would be zero, but when it was on, there’s nothing to pull it up.

Interesting, I definitely would have done it the second way…figures. It would be cool to try it.

 

I just started digging and the only available pwm pins are min endstops, Fine don’t need XY on the mini, Z maybe a probe. Or they can be flipped max to min then the…anyway rather not use these. The others are on p3 TX and RX, I’ll try these now.

Or, even easier:

5V – Rpullup – FAN/OUT.

10k pullup, pulls it to 5V when floating.

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That wouldn’t pop anything, 5v and 12v circuit mixing?

Well crap, the list was wrong schematic was right, the only PWM pins are endstop min. I think it would cause some waves if I flipped the min’s to max’s. So the best way to go about using the laser 5v ttl/pwm is the way described here and on the mini page, bummer. This is going to come back up with some PID users. That is going to take two free pins, I am going to have to flip X and Y…shoot, should I just do it, or make a whole new firmware? How many people actually use endstops on a mini?

Cap, there are some instructions here on using the min pins. I am not sure I am ready to flip endstop pins yet for everyone, that could cause some irritation.

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Ryan/Jeff - you guys never cease to impress me, good stuff. I don’t quite understand the lingo yet…but I’m working hard to get there. It’s like learning a second language!

I’ve been messing around with lightburn today and the gcode it generates. After tinkering with the settings a bit and talking with their customer service reps via email I was able to figure out how to drop the power below 20%, which allowed me to actually burn a grayscale image (I think!). Pic below of some of the test burns I did today. The difference between Red Oak, Pine, and 1/4 plywood were pretty distinct…Red Oak burned much better than the others for me.

[attachment file=“Test Burn.png”]

Thanks again for all the great advice.

That looks great. The difference between dithering and grayscale on the pinwheel is pretty obvious. Maybe try etching a rectangle at the lowest setting where you can still see something. That would give you a good starting place for the min. I don’t use a laser, so that’s just a guess. If I were you, I would definitely make a bunch of stuff before I changed anything. Might as well, in case you break it later :).

For anyone interested in the 5V fan pin discussion, I did some experimenting tonight too.

Turns out… I was WRONG. That won’t work. Because they wired in an LED to show when the fan is on. So if you put a resistor between FAN1(-) and 5V, you get this (when the fan is off):

12V – 1.8kOhm resistor – LED3 – FAN1(-) – 10kOhm – 5V

Schematic here (I love open source): https://reprap.org/mediawiki/images/4/41/MiniRambo1.3a-schematic-pg4.svg

So the pin ends up at 10V or so.

What I did instead is connect a smaller resistor between FAN1(-) and ground and tada (that’s 5V).

[attachment file=62262]

This looks like this:

12V – 1.8kOhm – LED3 – FAN1(-)/OUT – R2 – GND

The voltage at that pin is:

(12V - LED) * (R2/(1.8kOhm + R2))

With an R2 of 1.5kOhm, I get 4.7V. The LED voltage must be between 1.5-2V.

It has it’s problems though:

  • M106 S255 turns OUT to ground, M106 S0 turns OUT to 4.7V. That’s inverted for most people (and maybe most CAM).
  • The resistor value needs to be kinda close. Bigger resistors and you’ll get a higher max voltage. Lower values and you’ll get a lower max (and it might not trip). It’s a balance between that 1.8kOhm resistor. You could get 3.3V out of this too though.
  • It’s mini-rambo specific. There are different setups for different boards. If they replaced the 1.8kOhm with something else, you’d need to find a different resistor.
  • It has to be the (-) terminal. The (-) is farther from the USB plug.

It is a simple fix though.

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The things we do for fun… To skip all that is there some sort of logic translator, kind of like with the PID, read the 12v PWM output 5v? I suppose this might have some sort of lag though. Just looking for a more universal solution.

What about grabbing the signal right at the mosfet leg, isn’t that 5v and the mosfet directly changes it to 12v?

I wouldn’t hold out hope most people could solder that. The leg is bigger than most spots, but…

That will be fast, but 1) it’s still inverted and 2) you’ll still need a pullup resistor. Any resistor will do though, and you’ll get 5V pretty much exactly. You need to wire in 12V and 5V to it.

I can certainly imagine something that would connect just to the two sides of FAN1, Rambo GND and the TTL and GND of the laser and do this. If we wanted it that badly. It would be hard to compete with a resistor or a $4 board with more wires or just a firmware change.

The mosfet is actually the 8 pin SMD right “above” the fan pins. That would be a tricky solder.

Fellas, checking to see if there is anything I can do to help. While I don’t personally have the gear to test things on the laser driver board I know someone who does. If I know what type of info would be helpful and what instrument would be able to obtain that info it I can make it happen.

Thanks

Thanks for the offer. On my side I am going to put it to the side until I decide what to do about the firmware. I Think I am going to just make another branch (oye, so many) specifically for laser and PID with the pins flipped. Not sure what Heffe has up his sleeve though.

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Cap, thanks for the offer. We kind of took over your thread here (sorry). If you (or anyone reading) was interested in using the 5V TTL from the FAN pin, I could troubleshoot it with you, but I’m not chomping at the bit. I’ve scratched my itch, so to speak.

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Good deal, had to ask! I thought the discussion was great, look forward any future firmware updates that might be coming.

That being said the laser is doing pretty well as is. I’m dialing in the grayscale settings and am getting much better results. I’m getting PWM of sorts as I watched the fan speed on my LCD fluctuate gradually up and down during a grayscale burn.

I don’t plan on going grayscale much, I’m looking for lettering and logos, which this setup is perfect for. For anyone else looking for the same I wouldn’t hesitate to recommend this laser with the mini Rambo. It’s simple and it just works.

Last couple of gray wheel burns

[attachment file=62326]

Test on aluminum with flat black spray paint. The initial cut was pretty clean, the edges chipped a bit when I was rubbing off the soot.

[attachment file=62327]

Thanks again

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I am starting to get interested in these lasers after following this thread. My big concern with these is picking the right glasses to wear when watching these. What glasses do people use with these? This looked like the right type to wear, but this is something I do not want to skimp on cost if they are not the best. https://www.banggood.com/Red-Blue-violet-Laser-Safety-Glasses-Laser-Protective-Goggles-Eyewear-p-955972.html?rmmds=detail-top-buytogether-auto__1&cur_warehouse=CN I know this wattage is mostly for engraving, but are there materials this can burn through, like leather?

I got a free pair with the 2.5W laser I first bought from banggood, and honestly, it was uncomfortable looking at the spot where the laser was burning the work piece. I never felt like they did a good enough job of protecting my eyes, so I would just avoid looking directly at the spot as much as I could. I recently picked up a pair of these, and they are absolutely fantastic. Certainly a significant price jump from the ones you linked, but I personally feel much better protected using them. Just a data point for you.

As far as cutting with a laser, the 3.5W I got later from banggood will cut through 6mm plywood and acrylic after a few passes. Haven’t tried leather, but I would think that would work too.

Covering the widest spectrum possible is the best bet. Those laser very easily could be out of spec. Those glasses look amazing. I got mine from them but used a different pair, I would have gotten those if they had them at the time.

Thanks for the info. I will add that link in case I decide to add a laser to my MPCNC. I am sure it is well worth the extra money for a good pair of glasses.