Laser setup troubleshooting LD voltages

LowRider CNC Troubleshooting
1

I’ll apologize at the start for being a bit long-winded. I tend to overcomplicate and overexplain things. :sweat_smile:

I have no real background in woodworking, electronics, or almost anything else related except for a touch of programming experience and flashing custom ROMs on phones, so building a Lowrider v2 has been an adventure and a steep climb!

I have my LR2 up and running and can successfully draw a picture with a pen strapped to the tool mount. With that out of the way, I moved on to setting up the laser as my fiance wants me to wait on routing.

I am using a RAMBO 1.4a board with a laser driver from techhood on eBay (but it looks different from the picture) and am following the instructions from “The 2.8 watt, $100 Laser Upgrade”.

When I test via pin 45 on the RAMBO with the laser set at 255 and 127 power, I get results of 5V & 2.5V respectively. When I connect the driver, however, I’m getting stuck.

The instructions reference two adjustments to be made, one for current and one for voltage. I am only seeing the one for current (but no amount of turning makes the only LED turn off) and the only screw is not actually on the board but underneath it and doesn’t appear to have any effect.

If I adjust the one that the instructions reference for current until I get the voltage at 5.5V, I can then use the RAMBO to adjust things but the voltage doesn’t change as I would expect it to. As I drop the laser power from 255 towards 0, the voltage drops slightly from 5.5V, rises to 6.2V, then drops slowly again as it curves back towards 0V.

I have included some pictures of my temporary set up so that you can get a better idea of what’s going on.

My Rambo board with TTL wires:

PXL_20201222_224233357
PXL_20201222_2242333573024×4032 3.13 MB

The driver:

PXL_20201222_224309836_2
PXL_20201222_224309836_24032×3024 3.14 MB

The voltage outputs I’m getting from the LD pins on the driver for the corresponding laser values:

desmos-graph
desmos-graph800×800 39.2 KB

2

You are not looking at the correct thing with your multimeter. The output from your RAMBO board is PWM. This means that the +5v signal is being chopped up at (usually) 20kHz to represent the required output. with a signal setting of 127 the duty cycle of the signal will be 50/50 and with a signal level of 255 it will be 100% on. Your multimeter is just averaging out the pulses to show you 2.5V and 5V respectively. The VOLTAGE does not control your power supply, the duty cycle does.

The instructions for the laser driver power supply will require you to set the Maximum drive current to the LD…nothing more, so set the Rambo to 100% power and tune the power supply for the maximum stated current your LD can manage (less a small margin if you wish) and you are done.
The relationship between the voltage and the current settings in your power supply output is constrained by Ohm’s law…you cannot alter one without affecting the other.

you would also appear to be trying to measure the power supply output without a load. This is asking for trouble. Remove your multimeter wires from the power supply and fit the laser diode, lookup the correct maximum current rating for the laser diode, it should specify a max current at a voltage, turn the adjustment pot to MINIMUM, if you are not sure which way minimum is set your RAMBO to 10% (power level 3) and twiddle the pot for minimum laser output, then switch off and reset RAMBO to 100%) switch on (after taking all required precautions) and measure the voltage across the laser diode…set it to the maximum you are happy with.

3

I figured I was missing or misunderstanding something. Thank you! I’ll give this all a go in a bit and let you know how it goes.

4

My brain is not letting me grasp what is going on right now. I think I’ll have to put this on hold until after the holidays. Between not having done much stuff along this line, having medication that affects my concentration and memory, and going through and putting my business on hold for a month of lockdown starting Dec 26, I don’t think I have mental capacity left, lmao.

5

Good idea if you are not comfortable with it you don’t want to be messing with lasers.