In the next series of “stuff I have to build so I can build a laser” is a meter for measuring the output power of lasers. I already have one of these I built a while ago, but it can’t read the power levels of the laser I want to build.
After a lot of soldering, 3D printing, calibrating and debugging, here’s the result:
Finished power meter using a used Ophir laser sensor I bought off eBay.
It’s rechargeable through a USB-C connector, tracks maximum and average values, can log data for up to five days, and even show the logged data on a graph. It will measure up to 120 watts of laser light (briefly; it will overheat very quickly at that power level).
Here are a few action shots:
This is built on an AtMega328 processor running at 20Mhz and a 24 bit precision analog to digital converter that’s accurate down to something stupid like 10 nano-volts. But this made it easy for me because I didn’t have to implement different ranges. If you plug the device into a PC it shows up as a serial port and you can download a saved log.
The guts. OK, there are a couple of hacks I had to do to make this work (resistor on the left and the blue jumper wire), but this was the first board revision so great that it works at all. Note the really cool programming connector — I searched for a while to find something I could just clip to a board and not have a physical connector. That allows the board to be a lot flatter and this is about 1/3 the size of the normal pin header. It also provides serial debugging capability to the microcontroller.
Logs and configuration data are saved in a 64KB flash chip. The AtMega328 does have both flash and A/D, but too small and not enough resolution for this.
I put all the details up on GitHub for anyone who wants to build their own. Because yeah, a lot of people are going to be clamoring for this.