Intro: Reuse That Old Thrift Store TV
I have a great love for CRT televisions. Especially small ones form the 80s and 90s. A few months ago I found one at the junk shop. Color, still working, $10. How could I say no.
The plan is to build a tabletop retro gaming console. The CRT will display video from a Raspberry Pi and an external amplifier will pump out the music.
The great thing about CRTs is that you can quite easily modify them to display music as wave forms. A sort of simple oscilloscope.
This adds the unique ability to either play a game and listen to the music or listen to the music and watch the waveforms on the display.
To complete a project like this you will need to have basic soldering skills, beginner level programming knowledge and access to a laser cutter or wood shop to build the case.
Remember working with electronics can be dangerous so be careful.
1x 5" portable CRT television
4x 1/4" machine bolts with nuts (for mounting the TV)
1x 12v 10-20 watt amplifier (sells on Adafruit for $20)
1-2 small full range speakers
1x 12v power supply
1x 12v to 5.2 v converter (or an old car cellphone charger)
1x Raspberry Pi Computer (any model)
1x DPDT switch (style is up to you)
1x SPST switch (for power)
1x 10 Ohm panel mount Potentiometer
1x Knob for Potentiometer
For the case
1x Sheet of 1/4" plywood (about 24" x 24")
Wood stain (dark)
Shellac Paint brush or rags
Step 1: Beginning: Modify the TV
There are basically three major parts to this build
1) Modify a small TV into a music visualizer and find a way to feed it composite video
2) Build the wooden case
3) Wire the Pi, the amp, speaker and the TV together
Modify The CRT
There are plenty of tutorials that will show you how to turn a CRT television into a music visualizer. I'm not going to explain all that but here are a few links that will. Remember CRT use very high voltages, larger models can be quite harmful if you are not careful. Do some research about safety procedures before you crack one open.
Adding Composite Video input to the TV
These old TVs were designed to pick up analog video signals that were broadcast over radio waves.
They do not always have video input but some do and that is by far the best model for a project like this.
You can also use a device call a RF modulator. They are designed to turn a regular video signal into a signal that the radio receiver will recognize. These are easy to set up but they have less than great video quality and it means you have one more device to power. Still that would be the easiest way to add composition video to these old TVs.
The most difficult but best way to add video input to an old TV is to find the video amplifier on the circuit board and tap into it. This can be a frustrating trial and error process but sometimes you can google the make and model of the TV and find the schematic which helps a lot.
I lucked out and found the schematic and was also able to look up the specks on the integrated circuits used on the TV. On this TV there was a pin on one of the irrigated circuits that was labeled VIDEO IN, turns out that was all I needed to find. Each model TV is different and its not always this easy.
Once you find the pin for video you can solder a wire directly to it and solder another wire to a ground point on the TVs circuit board to create a video input for your TV. I wired this directly to the video out and video ground on my pi board but you could wire this to an RCA plug if you want to be able to easily disconnect it or plug different sources in.
Keep in mind most of the old portable TVs in the world are black and white. Don't be discouraged if you have a black and white one. They usually have better resolution and you hardly miss the color with games that never had it, like all the original Game Boy games.
Step 2: Build the Case
You can build yours in any style you like. I drew inspiration from vintage ratios and very early tube TVs.
I used a laser cutter to create the case out of standard 1/4" plywood. If you have access to a laser cutter this is a very affordable route to take but you could also build something nice with hand tools. At the end of the day it's a box so don't over think it too much.
Before you start designing the case take out all your materials and lay them out on a table. You need make sure the case will be big enough to fit the TV with its circuit board as well as the speaker box, the amp and the Raspberry Pi. This is a bit of a puzzle so take your time make sketches whatever. You can even build a cardboard prototype just to make sure everything will comfortably fit.
I used a free box generating program to create a PDF of a box that is the size I need. Then I imported the PDF into INKscape to make some edits. (like adding the speaker gill, the cutout for the screen and holes etc.) If your PDF has any words on it ( the free generators will often put there name on it) you will want to remove them. Your PDF should have 6 panels top, bottom, left, right, front, and back. You will want to find the font and back panels and add some holes for the tv screen, and speaker as well as all the switches and ports.
Be sure to think about where all your switches will go and make sure you don't forget anything! In my case I wanted to keep the front panel simple with the TV screen, speaker, a knob for volume and a switch to change between video and music visualizer. On the back I have the jack for power, the aux audio jack and two power switches (one for main power and one to keep the raspberry Pi on or off).
Once you have a design that you are happy with load it up in the laser and fire away! It may be a good idea to cut one out of cardboard first that way you can make sure everything is how you want it before cutting your material.
It is a process but well worth the time.
Always sand in the direction of the wood grain. You can use an orbital sander to save time but you may see tiny circular scratches in your final finish. The wood conditioner is an important step. It causes the wood to swell a bit and some if the grade will pop up, that is why we sand after to bring it down again. The conditioner also preps the wood for the stain so it takes the color evenly without blotchiness. More than one coat of stain will give you a darker finish but I found this was not needed.
1. Sand with 220 grit sandpaper, sand off any charring on the edges
2. Apply wood conditioner, wait to dry, 10-20 mins
3. Sand again with 220 grit, use a block of wood apply even pressure
4. One coat of dark stain, let dry
5. Apply 1 coat of shellac, let dry 1 hour
6. Sand lightly with 300 grit
7. Apply 2nd coat of shellac, let dry 1 hour
8. Use some wood glue to glue the bottom and side pieces together. I did not glue the top panel because you need to be able to remove it to access the inside
You may also want to build a box to hold your speaker. You do not need to but having the speaker in a MDF enclosure will give you much better sound. It's work the extra step. I used a 4" speaker from Adafruit and built the speaker box using a table saw. It's about 5" X 5" when all is said and done.
Now its time to wire it all up!!
Step 3: Wire It All Up!
OK the Final Moment! You have your box and all the electrical components. The last thing to do is fit everything inside in a orderly way. You will need a spot for the power, the amplifier board, the speaker, and the TV with its circuit board.
Notes on Wiring
I used a 20 watt amplifier board which sells on Adafruit for about $20. I am also using a USB dongle Digital Analog Converter (DAC) on the pi to get a better sound out of it. The dongle is sending music to the amp and the the amp is sending its right channel to the speaker and its left channel to the TV. I wired a switch on the front of the box so you can switch between viewing the video or seeing the sound. This is important because you can only do one at a time if the amp is connected to the deflection coil of the TV you won't see the video, and vise versa.
If you are confused by how this works check out the websites I cited on the first page. There is plenty of info there to explain how the music visualizer works and how to wire it up.
Notes on Power
Most portable televisions run off 12v DC at about 1 amp or less, this was so they could be powered on the go from a car or boat battery. That is great because the 20w amplifier I have also runs off 12v and even has a pin out specifically for powering another device with 12v. I have power supply hidden behind the speaker that is converting the 120 AC volts from the wall to 12v and this is wired to the amp of the TV and the Raspberry Pi power supply in parallel.
The Raspberry Pi needs only 5v and tends to self destruct if it gets any more than that. This means we will need to use convert the 12v to 5v for just the pi and then everything can have one main 12v power supply. You can buy a boost converter, or use a 5v regulator, but I have found that old car cell phone chargers can work very well and can usually be found for free or very cheap. That is what I am using to power my Pi and I covered it all with electrical tape to prevent any shorts.
Note on the Raspberry Pi
I am using a Raspberry Pi 2 running Retro Pi. I have the Pi outputting composite video instead of video from the HDMI port. I am using a DAC to get better sound out of the Pi. I also mounted the pi in a very accessible place that way I can change the SD card or plug things into the USB ports, like a wireless gamepad or bluetooth dongle etc. If you use the new Raspberry Pi 3 or the Pi Zero W you they have bluetooth built in but I still recommend using the a DAC because it will sound much better.
That's it! When everything is in place you can power it up and have a go! One thing I would do differently is I wish I had added more ventilation to the box. There are a lot of components in here and they get hot! I always turn it off completely when I'm not using it because letting heat build up inside could damage circuits or worse catch on fire!
I hope you enjoyed my post and are inspired to give your old TV a makeover!