Serving The Feline Masters: A Chair To Follow The Sunny Spot

Terry Pratchett once wrote, “In ancient times cats were worshipped as gods; they have not forgotten this”. [Jonathan]’s cat has clearly not forgotten, and makes it loudly known whenever her favorite chair needs to be moved to stay in the spot of sunlight. He was looking for a fun hack anyway, so he decided to give in to her majesty’s demands, and automated the task.

[Jonathan] first considered adding motorizing the chair itself, but decided to keep it simple and just drag the chair across the room with a spool attached to a motor. The rope spool was attached to a small geared DC motor, mounted on a salad bowl base, and connected to an ESP8266 via a motor driver. The ‘8266 is running  NodeMCU with a web server that accepts simple motor commands through a RESTful API. This setup can’t reset the chair to it’s starting position at the end of the day, but this is a small price to pay for simplicity. The motor was a bit underpowered, but it only needed to move the chair in small distances at a time, so [Jonathan] removed the chair’s back to reduce the weight, and upped the motor voltage.

Determining when and how far to move the chair is the second part of the challenge. [Jonathan] considered a simple lookup table for the time of day, but the motor’s movement wasn’t consistent enough. The final solution was a set of three BH1750 digital ambient light sensors to give feedback. A pair of sensors on the chair determines its position relative to the sunny spot, by comparing light levels to a reference sensor mounted in the window. These light sensors are also attached to NodeMCUs, and send movement commands to the winding unit as necessary.

Unfortunately, it appears the hack was in vain, due to the end-user being frightened off by the motor noise. However, it still helped [Jonathan] to scratch his hacking itch, and fortunately for us, he documented the adventure and shared all the code.

This is the first cat chair we covered, but we have seen a few hacks to feed them or keep them away.

21 thoughts on “Serving The Feline Masters: A Chair To Follow The Sunny Spot

  1. Hmmm. Motorized chair without a cat. Useful. I would have made a heliostat. Plastic mirror, couple servos. Maybe a Fresnel lens. Probably wouldn’t need a processor. Just a couple 555 timers. No cat-frightening involved.

    1. I think if you had Fresnel lens segments like vertical blinds, and controlled, you could keep the sun spot confined in the E-W dimension… then maybe another horizontal set for the N-S dimension… Unless you wanted to put one set on a frame that rotates.

      1. A fresnel lens and mirrors (heliostat) to keep the sun focused on the chair might end up with a hot kitty…and could end in Cat-tastrophe. He could be charged with running a “Hot Cathouse”

  2. If the motor worked slowly all the time, it wouldn’t make noise frightening the cat. It can calculate the current position in any time from LUT values. It would be more accurate than large steps even without regression – it can just assume that position between LUT points changes linearly.

  3. The chair seems to be mostly unpolluted by cat. The motor noise would seem to be an issue so I would suggest keeping the sun stationary by halting the earth’s rotation, thereby giving the cat a restful sleep. Alternatively, rotating the building to keep the beam angle constant. It’s the least you can do.

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