Hot tub cinema

My spouse got the idea that the dull gray inside of the hot tub cover might work well as a video projector screen. I remembered that my friend had an extra projector that I could have for a song, so why not try this out?

The projector

The projector I got was a really flimsy Vivitek Qumi led-projector with meager 720p resolution, but on the upside it’s small and looks like that it might endure the extreme temperature changes here in Finland. The projector came with no mounting plate so the first thing was to design and print one. This was quite easy considering that the projector is really light and has a standard camera thread on the bottom. I came up with this design: https://www.thingiverse.com/thing:4796449

The computer

I needed some hassle free way of playing videos. The simplest approach would be to use the projectors in-build USB-player but it would probably only play a really small subset of videos and adding those would be cumbersome. With good experiences on prior project, I chose Raspberry Pi 4 as a computer and installed LibreELEC distribution to the smallest SD-card I could find from the parts bin. LibreELEC is a tiny Linux distribution containing only what’s needed to run Kodi, a popular easy to use home theater software. It boots fast and runs from a small SD-card. To mount the Raspberry, I printed my favorite enclosure from Thingiverse: https://www.thingiverse.com/thing:3714695.

The entertainment

From the moment my spouse presented the idea, I had a clear vision what needs to be organized: A demo watch party for friends, so I collected computer demos from my favorite groups: ASD, Farbrausch, Fairlight and others. My spouse collected nature videos with relaxing music etc. We stored all the videos to our home server and instructed Kodi to automatically play a selection from the network share at startup.

Putting it all together

I fixed the projector under the eaves of our house where it would be safe from rain and only less than three meters away from the hot tub cover. The Raspberry case has VESA mounting points which were used to screw the case under the eaves. Our terrace has only one somewhat broken electricity outlet so that forced me to run an extension cord along the wall. The future improvement will be to run the cable inside the boarding. I put a remote controlled outlet between the extension cord and the outlet doubler to serve as an on/off switch for the whole system. The projector has its own power supply and I found an extra mobile phone charger to power the Raspberry (I used 4A supply and would not recommend using any less. Decoding videos takes a lot of juice). The picture showed up nice and bright enough in the early spring nights. Using the projectors zoom and trapezoid correction I got the picture to fill about all the space available in the cover. Even after adjusting, the picture is not perfectly sharp but for mostly playing abstract videos for ambience it’s fine to me. A water-proof Bluetooth speaker was used for the audio and controlling the Kodi when needed can be done using a Kore application on the Android phones.

Not only dance and joy

I was happily surprised how easily the project came together. That being said I did end up climbing up and down to the projector and adjusting the picture numerous times. The reasons were bad wifi speed and projector going to error mode.

Wifi speed

My mistake was to tidy the wires by fixing the projector PSU on top of the Raspberry with a zip-tie. The RF-emissions caused the wifi speed to be anything between 0.1 Mbps to 20 Mbps and making streaming videos from the home network painful. This was easily fixed by moving the PSU farther away from the Raspberry

Projector shutting down

I was a bit skeptic how the projector would handle the freezing cold weather. To my surprise it seemed to work in the minus five degrees weather. For a fifteen minutes. After that the projector started to blink the panel lights and according to manual indicating “CPU Fan fault”. Turning the projector off and on again resulted again 15min of use time before the same repeated.

I took the projector apart and tried to clean it up. I could not see any obvious problems. After putting it together this problem happened only once. I’m not sure if this is really about the fan or just the cold weather. It’s now a bit warmer so that might have fixed it. If the problem reappears the next winter, I’ll probably just add a second remote controlled outlet to flip just the projector off and on again.

After these issues were solved the installation has been working fine and endured outside already a month of quite terrible spring weather!