# Laser - PWM voltage 3.3V

I have this Laser lying around from AliExpress, after I did send back another one from Amazon which were way beyond expectations. (7000mW)
So this one is the 6000 mW variant, and I’m still waiting for some fans. I want to use them for both air assist and additional cooling.
In the AliExpress description it’s stated the PWM frequency is 3.3V. The other one was PWM 5V, and I managed to run that well on remapped Pin44.
Now I’m a bit confused about the 3.3V. Does the Ramps board even have pins that supply 3.3V and I need to do a remapping similar as I did with Pin 44 on the other Laser. Or might I just hoping that this one doesn’t mind the 5V, only thing bis the 100% are reached at 3.3V what should be around 70% on the normal Pin 44, or do I put something in front of the PWM signal. a resistor would be the simplest thing I guess.
I know there are some Laser- enthusiastics among you who faced the same question already long time ago.

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The microcontrollers output is 5V, so that’s generally as low as it would go. The output from something like pin44 is either 5V or off. When you drive it at 70%, it is just 5V for 70% of the time.

It’s very possible that it is 5V tolerant. But if it says 3.3V, then you’re taking your luck in your own hands. Putting a 1k-10k resistor between them adds a little safety, because if the extra voltage is going to break it, it will at least be current limited by the resistor, and when current goes through the resistor, the voltage will drop, potentially saving the input.

There are some ways to get 3.3V though.

1. Use a resistor divider. Since the input to the laser isn’t drawing any current, you can use some resistors to drop the voltage.

Rambo – R1 – Output – R2 – Ground

If you wired it like this, then R1/R2 should be about 0.5. So a 10k and 20k resistor would do it. It doesn’t have to be exact, a 22k for R2 is fine. Even if you just use two of the same resistor, the output would be 2.5V, which is enough to trigger a 3.3V signal. The total R1+R2 should be more than about 5kOhm, so you don’t stress the arduino pin.

If this input takes any current though, these calculations will be off. So it’s not good for loads. Just logical inputs.

1. A 3.3V power supply and a logic level converter. There are boards that do logic level converting, both ways, which are made for this kind of thing.

You need to wire HV to 5V and LV to 3.3V.

1. A transistor and a 3.3V power supply. It’s basically what the logic level converter is doing. You would need a pnp and connect a resistor to ground on the output to draw enough current to get it into saturation.Thia really only makes sense if 1 doesn’t work and you already have the parts.

Personally, I would probably just hit it with 5V…

Thanks mate, I’ve got plenty of resistors here anyways. Easy thing. When I remember the other Laser I had. I put the full 12V of D9 on the 5V PWM, and it survived it. Luckily enough I changed the PSU b4 as I was running it on 19V b4.
I would feel confident to hit it with the 5V too, but then again, you have to keep that always in mind with all the jobs you do with the Laser.

I really like using these guys for shifting logic levels:

https://www.amazon.com/gp/product/B06XWVZHZJ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

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Tinkered a bit with it today. Found a couple of resistors what brought me pretty close to the 3.3V. (a6K7 & 12K if my mind serves me well).
Well not much happened, the Laser fired somehow randomly, but not when M106 SXXX was send. Same when I connected the PWM signal directly to Pin 44. At that point I did stop, as I had the laser only on a 2A PS. I ordered a 12A when this one and my other gimmicks arrive, amongst one of this cool 20\$ scopes another user uses here, I’ll give it another go, straight from the board just to be sure.

Does it turn off when it’s supposed to be off?

No, it looks a bit like it has it’s own life.
At present, I blame the weak power supply for it’s behaviour, so I’m waiting for another to arrive.
Maybe using simple RGB-Led cable was a bit optimistic too.
As said, I’m waiting until the PS arrives, then I will test it straight from the board, and move from there.