As of last year I had worked all the major bugs out of my motion-tracking eyeball, but I still couldn't consider it finished. I wasn't ready to hang it on the wall and let it operate yet, due to one last issue: thermal concerns.
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| It's installed on the wall! It's operating continuously! It's done! The Lab Assistant gets to take a nap! |
The eyeball's motion is driven by two unipolar stepper motors, each of which is powered from one of my dirt-simple stepper motor controllers. These are custom PCBs that I got manufactured many years ago. They were very inexpensive, and they only have two control wires (a nice thing for connecting motors to embedded processors with a limited number of general purpose IO). But that also means they don't have a power enable. Even if the control inputs are static and the motors aren't moving, some of their coils remain energized. That means they can exert their holding torque, which keeps the drive shaft in place and resists any external forces that try to turn it. But that wasn't something the eyeball needed (it naturally stays in position when unpowered). And during tests, I noticed that the motors got quite hot: enough to be uncomfortable to touch and make the plastic case smell.
I didn't like the thought of leaving the eye turned on with the motors baking themselves and everything else in the case in their own heat day in and day out. I doubt it would qualify as a fire hazard or anything serious like that, but in addition to wasting a small amount of electricity, it could reduce the lifetime of the parts. So I wanted to be able to cut all power to the motors when the eye wasn't active.
My solution was a standard relay. I bought some of these nice little breakout boards from DIYables that have the relay already mounted with connectors and a couple of indicator LEDs, and spliced one into the motor power input path of both motor controllers.
Then I added code to the eyeball software to turn the relay on and off. I wanted to strike a balance between letting the motors heat too long, and clicking the relay on and off constantly. So the software turns the motors off if no moving object to track has been seen in view for a certain amount of time. I also threw in darkness detection; the eye will stop trying to track motion if the average brightness of the scene is too low to see properly. (So it won't move around and make little noises in the middle of the night because the camera picked up some low-light noise.) Both features worked very well. The eye reliably deactivates when I leave the room (so long as there isn't something else moving around, like the flames in the fireplace) and when the lights are out or too dim.
In the dark, the indicator LEDs on the Raspberry Pi and the relay board diffuse through the white parts of the case and turn the eye into a low-key nightlight. I wasn't really expecting this, but hey: it still has a function when it's not looking at stuff.
In the end, I got to do what I always wanted: hang the eye on the wall and let it be an always-on fixture in the house. Further tweaks and upgrades to the software are possible, but I'm calling it finished because it's finally operating. It has been on the wall trying to look at me, the Lab Assistant, and other motion sources for at least a couple weeks of total up-time. Hearing it "wake up" as I pull open the curtains has become part of the morning routine.
There will almost certainly be another version, because there are plenty of things I could improve. I already applied a bunch of little enhancements to the 3D models of the case parts late last year. But this is the first Atronach's Eye iteration that could be said to realize my original vision (cough) for the project, if imperfectly. I'm also thinking about what else I can do with it. Atronach could theoretically tell Acuitas whether there's somebody in the room, for instance. Mmmm.
Until the next cycle,
Jenny
