Laser Power Meter

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parkview
Master Maker
Posts: 448
Joined: Tue Jun 24, 2014 8:25 pm
Location: Busselton
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Laser Power Meter

Post by parkview » Sun May 10, 2020 3:45 pm

It's a joy to have and use a CO2 laser cutter. Over time, I have wondered if the tube's power might decline. If so, by how much? Also, the machine came with a set of three 20mm mirrors. The back's of the mirrors heat up quite a bit, so therefore they are not close to 100% efficient reflectivity. All of this has been had to quantify. While I have added on a tube current meter: http://forum.swmakers.org/viewtopic.php?f=9&t=189 I thought it would be handy to be able measure the laser beam power it's self. To this end, I purchased a way over priced (for what it is) Mahoney laser power meter, but it didn't really live up to it's hype and it could never be properly zeroed. Here it is in a bench vise:
laser_meter_sml.jpg
laser_meter_sml.jpg (62.85 KiB) Viewed 456 times

Back in late 2016, I started experimenting with using a MAX31855 thermocouple connected to a thermal mass being read by a Arduino Nano, with the results being displayed onto an OLED. I experimented with a few different aluminium 6161 masses to see what might work best on my laser. It seemed to indicate that there was quite a lot of power loss after each mirror. Below, I am testing the third and final mirror, with the mass held in place on a purpose designed 3D printed suspension:
third-mirror-testing_sml.jpg
third-mirror-testing_sml.jpg (69.66 KiB) Viewed 456 times

It's time to have a go at putting all the electronics onto a small dedicated PCB.

parkview
Master Maker
Posts: 448
Joined: Tue Jun 24, 2014 8:25 pm
Location: Busselton
Contact:

Re: Laser Power Meter

Post by parkview » Sun May 10, 2020 4:01 pm

It didn't take long to quickly whip up a circuit diagram that's powered by a STM32F042:
Laswer Power Meter - Schematic V1.0_sml.jpg
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The results are displayed on a small 128x64 SD1306 OLED screen. There is a buzzer mounted under the PCB to save space and allow the OLED screen to be mounted closer to the yet to be 3D printed housing:
Laser Power Meter PCB_sml.jpg
Laser Power Meter PCB_sml.jpg (37.17 KiB) Viewed 455 times

The small 63mm x 18mm PCB to hold all the circuitry except for a button or two, which will be cabled and soldered into place. I suppose if I had designed up a housing first, it might have helped me to decide on which type of switch and it's corresponding footprint. Now I have the luxury of time to complete the housing while I wait for the compact PCB to arrive:
Laser Power meter_Board_sml.jpg
Laser Power meter_Board_sml.jpg (31.4 KiB) Viewed 455 times

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