Functional Eclipse Computer

I have progressed on the eclipse computer project past a prototype to something that mostly works. There a few minor bugs in the code, but it is usable as-is. I’ve got fixes for them, but need to test before committing. The system still doesn’t use its buzzer for an audible prompt, and I haven’t written anything yet to help take a sequence of pictures showing the progression of the eclipse. I may not get to that for a day or two to deal with travel related issues. I plan on taking it, and a bunch of camera gear, to the Nashville area to view the eclipse.Eclipse ComputerThe picture shows what is nearly the final hardware, but older software. This video shows the current software. The hardware changes between the two are all to help keep everything from moving around in the case, and to keep the barrel connector that supplies power to the upper breadboard close to the board. The connector was moving away from the board too easily and causing a reduction in the supplied voltage.

All of these problems were solved by applying solid copper wires in the right spots. I use solid copper with breadboards a lot because I can cut the wires to the length I need and the conductor is stiff enough to be inserted into the breadboard without tinning or the addition of some connector. I used a few more of these wires to hold down the barrel connector and to apply some pressure against the top of the case. It worked out quite well.

I changed the display from a 16×2 LCD to a 20×4 one just for the additional text. The video shows how I’ve made use of the space. The 20×4 display is a bit dark and needs a backlight to be readable unless it is in bright direct sunlight. The 16×2 display didn’t have this problem; it is more like a common digital watch display in how it handles light. I made and adjusted an automatic backlight control program that gets brightness measurements from a TSL2591 at its minimum gain setting and uses one of the Raspberry Pi’s PWM outputs. It seems to make the display readable enough in bright light and keeps it from being brighter than it needs to be most of the time. I’d rather have a 20×4 that is more like the 16×2, but I haven’t got the time.

I tested the computer running on 8 Eneloop NiMH 2000mAH batteries. For most of the test, the computer was indoors and used the minimum backlight setting. It recorded around 600mW power consumption under these conditions. In brighter light, power consumption got as high as 850mW. Working out a new times of totality can add about 400mW, but I wrote the code to limit how often that occurs.

The batteries kept the computer running so long that I couldn’t finish a battery life test in one day. The combined runtime before exhausting the battery charge was around 25 hours. That was much longer than I anticipated when I decided on 8 AAs. I’m still going to use 8 because I can, and the backlight will make the runtime a bit shorter, maybe 16 or 17 hours, about twice what I need. Also, a smaller battery pack would have more room to move about, and I already wrote low battery detection code based on 8 batteries in series.

I’ve got the Raspberry Pi Zero running Gentoo Linux. I made modifications to the configuration used by OpenRC to boot up the system so that it starts the program that provides information on the LCD and the separate backlight control program. A simple Bash script keeps re-running the software until it terminates without error, or the script is killed. No GUI is installed. I’m going to see if I can get it to set the clocks on my cameras, and bring up a network connection, when the corresponding device is plugged into USB. Nothing critical, but it would be nice. Hopefully plugging in a camera won’t cause it to reboot.

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