Hand tools and fabrication machines
A few months ago I wrote a post for the Hackster blog about Bitluni's CRT Boy project. I thought the idea of using a tiny CRT for a build was really cool, and on Twitter Emily Velasco (@MLE_Online) pointed out that you can find a used Sony Watchman online for less than $20. So, I ordered one and decided to turn it into a badge!
You can pick up a Sony Watchman for so cheap because they're useless for their original purpose. With the switch to digital TV broadcasting, there aren't any analog signals for the Watchman to pick up. And, obviously, everyone just watches videos on their phone anyway.
I figured it'd be fairly easy to find a way to inject a video signal, but it turns out it's not easy to identify where to inject it. So, my first version of this actually transmitted a VHF signal using an RF modulator. That worked, but the picture was poor and the setup was quite bulky—hardly ideal for a badge.
Eventually, after quite a lot of research and trial and error, I was able to identify the pins I could use to send a composite video signal directly to the CRT. Since the Raspberry Pi Zero W has a built-in composite video output, this new setup is nice and compact. Below, I'll describe the steps you can follow to do the same.1. Identify the Composite Video Pins
Be careful working with this! CRT use high voltages that are dangerous. If yours is like mine, however, the batteries will be disconnected when you take the back off—just make sure the CRT capacitors are discharged.
Some Sony Watchman models already have a composite video input, in which case you can just connect to that. But, most don't. Instead, the tuner module connects to a VIF chip that converts the RF signal into a composite video signal that's sent to the rest of the CRT circuit. So, you need to tap into that.
The problem is that there were alot of Sony Watchman models, each with many revisions. The PCB inside one could look completely different from the PCB inside another one, and different kinds of VIF chips were used. It took a long time to figure out, but in the case of my Sony Watchman FD-2A the VIF chip is labeled as "Sony 5350 CX20183".
Unfortunately, I wasn't able to find a datasheet for that chip—or even a schematic for the Watchman in general. As far as I could tell from other people's hacks, most of the Watchman models have a Mitsubishi VIF chip labeled as "M51364P". It's different chip, and doesn't even have the same number of pins. If you have that chip, search Google and you can find guides on how to find the video pins. If you have the same Sony chip as I do, here's where you can tap into the video pin:
First, find the Sony 5350 CX20183 chip, which will be on the underside of the large PCB. Use some snips to cut all the leads, and remove the chip. Then, flip the PCB back over and find the pads where it was soldered. You'll need to connect two wires: yellow for the video signal, black for ground. Video goes to the 6th pin down on the right side, and ground goes to the 10th pin down on the left side.
Use a little hot glue for strain relief and to make sure you're not making contact with any other pins. Then, drill a small hole in the back of the Watchman enclosure, feed the wires through that, and close the case back up.2. Print the Raspberry Pi Enclosure
Use the attached STL files and print the enclosure for the Raspberry Pi Zero W. I designed this one in Autodesk Fusion 360, which is free for hobbyists so you can also design your own enclosure if you'd prefer. This can be printed without supports, and should work with pretty much any settings (infill between 20-50%). I used PLA, but any material should be fine.
While that's printing, you can proceed the next step.3. Setup Your Raspberry Pi to Loop the Video
First, find or make whatever video you want to play on a loop. I just have a simple video that says "Hi there! I'm Cameron!" that I made in some free video editing software.
Then, setup Raspbian on your Raspberry Pi. Make sure you're using the version with the desktop. Then, copy your video into your home folder. I'd also recommend setting up SSH and connecting it to your WiFi, so you can make changes with needing physical access to the Pi (since it'll be permanently mounted in the enclosure).
Follow the instructions in this link to setup OMXPlayer so that it automatically loops the video on boot: https://www.raspberrypi.org/forums/viewtopic.php?t=1919424. Solder Raspberry Pi Connections
You'll need to connect the two wires from your LiPo battery connector to the 5V and ground pins on your Raspberry Pi. Here's the pinout:
The 3V3 pin is the one that's closest to the micro SD card slot. But, you're going to use the 5V pin not 3.3V pin. That's because the LiPo battery has a voltage of 3.7V and could damage the Pi if you don't go through the regulator connected to the 5V pin. The negative wire can just go to a ground pin (6 or 9).
Then, feed the video wires through the small round hole in the 3D-printed enclosure and solder them to the "TV Out" pins on the Raspberry Pi.
In this photo, the square pad on the left is where you solder video signal wire (yellow). The round pad on the right is where you solder the ground wire (black).
Then, use some hot glue to secure the enclosure to the side of the Watchman. Once it's in place, use a little bit of hot glue to keep the excess wire in place.
There is no power switch, so the Raspberry Pi will be on whenever the battery is plugged in. There also isn't any LiPo charging/protection circuit. That means the battery will just keep draining until it's completely empty—which actually damages it.
I didn't use a LiPo protection circuit because I wanted to keep this as compact as possible. Basically, that just means you need to be careful about how long you let it drain before you take it back out to charge. The Raspberry Pi uses a max of about 230mA, which means these 720mAh batteries should be good for about 3 hours. To be safe, I'd recommend recharging your battery after 2 hours of use.5. Wear It to Your Next Con!
That's all you need to do! Find a lanyard that fits through the hole, plug in the battery, snap the cover on, switch the Watchman on, and you've got a sweet CRT conference badge!