Tuesday, June 5, 2018

CRT and Magnets Exhibit

This Cathode Ray Tube + Magnets exhibit started off with a couple of CRT monitors that were gathering dust in storage. I was asked to consider putting them out in the main space of the makerspace. I decided I would only allow this if they did something. I set out to decide on what that something would be. It turned into a fun, easy, accessible to all ages exhibit that we now turn on for all the tours we lead through this makerspace. It is a great way to quickly and cheaply construct a meaningful interactive science exhibit to add to your collection.

Here's a document I put together to explain what's happening. I taped this to one of the TV antenna (the antenna is not used) so it stays front and center to the exhibit and people are encouraged to actually read it. Here's a lower quality image of the same document so you can see it embedded in the post.

Here's the bill of materials:

  • CRT television. You may have to turn to eBay or Craigslist. These may only get harder to acquire with time.
  • If the CRT has VHF/UHF inputs, you'll need a box like this one to convert the signal to composite video: https://www.amazon.com/dp/B0014KKV7W/
  • For the camera, the backup camera is cheap and outputs a composite video signal over RCA connectors. https://www.ebay.com/itm/CMOS-Car-Rear-View-Reverse-Backup-Camera-Parking-Night-Vision-Waterproof-7-LED/291918612347
  • If you'd like to place the camera elsewhere, you can get a cheap 2.4GHz transmitter like this one https://www.ebay.com/itm/2-4G-Wireless-Video-Transmitter-Receiver-Kit-for-Car-Rear-Backup-View-Camera/163041336550
  • A powerful neodymium magnet. You want something strong enough to have an effect and a good size to be easy to handle. Something like 0.5 inch diameter and 0.5 inch height seems like a good size to me, but I'd suggest just seeing what's available and trying it. You can always stack up multiple smaller magnets.
Assembly is just a question of plugging everything in to power and getting the signal in to the TV. Note that the backup camera requires a little work to plug in; it is designed to be hooked up to a 12V car battery connection point. You will need a 12VDC wall adapter if it does not come with one. You will need to make sure you have the red/positive connector and black/negative connector going to the right places. You will probably need to solder at least one connection, or use another strategy to connect the wires.

The magnet should be protected with something soft to avoid it hitting against metal and breaking or pinching fingers. I used two furniture feet and some masking tape. I also suggest putting it on a string so it doesn't wander off.

Cable management was the longest part of the project. I zip-tied all the extra length of cabling in back of the assembly. A single switch controls the extension cord to which the entire unit is plugged in. Note the CRTs make a high pitched noise that some people don't like to hear all day, so I don't leave it on all the time, since the main room of the makerspace is also a meeting and study space.

The cameras are taped to the top of the CRT and pointing at brightly colored pieces of paper. This is important because the magnet effect is not nearly as visible on black & white images.

An additional, optional modification I made to the back up cameras was the removal of the infrared lights that it contains in order to provide better visibility at night. The camera was very warm and when the IR lights activated, which sometimes happened if the exhibit experienced low light conditions, the image was washed out. I opened the unit and de-soldered the IR LEDs. My original plan involved putting gaffer's tape over the IR LEDs, but that seemed to make the camera heat up even more. There is a sensor inside the unit and in bright lighting the infrared LEDs are not activated, so this is not necessarily something that needs to be addressed for the exhibit to function.

It is also important to note that the backup camera is designed to mirror images. Note the sign in the image above is printed as a mirror image in order to show up correctly on the display. The backup distance overlay is another artifact of the choice to use a backup camera; I find it is fun and adds to the color distortion effect since it is displayed in bright colors.