A Skippable Introduction
Every year a deluge of new electronics rolls of the assembly lines and into already cluttered homes. It’s unfortunate that the majority of them will likely find their way into a landfill even before the next batch comes along. If they have any permanence they’ll likely be made obsolete in short order.
I don’t mean to sound crotchety. There’s nothing inherently wrong with replacing the old with the new. There are many virtues in upgrading to a newer computer whether to increase productivity or enjoy the newest video-game how it was designed to be played. Then there’s the other side, like the pointlessly wasteful disposable power bank.
Many products simply become obsolete and in that process we can find spectacular examples of humanity’s ingenuity. It’s incredible to think that a little less than a century ago the black and white television was the pinnacle of technological advancement. Now, OLED TVs are becoming more affordable and newer technologies are on the way.
Despite the introduction of color televisions in the late sixties it’s black and white predecessor managed to stick around in one form or another, even into the later end of the 90s. When I was younger I remembered seeing advertisements for various portable black and white CRT televisions. I remember wanting one, but never owned one due to the price. Now, a decade and a half past it’s manufacture date I got one, for a fraction of MSRP.
The Television in Question
Specifically what I bought for ~$5.00 from a Goodwill was a Claybrooke 5 in 1 Compact TV with an incredible array of features including a radio, flashlight, and even a compass. I would really like to know if ever anyone looked at one of these and said, “man, having a compass on this thing really sold me.”
Perhaps a reason for the low price was the missing battery cover, power adapter, and busted plastic bezel. Fortunately this wasn’t an issue as far as I was concerned, as I had no intention of keeping it’s original case. Perhaps a more practical bit of fortune was that it worked.
My plan for this CRT is clear from the title but there’s more to choosing a portable TV than the price and screen size. These portable models were designed to operate off DC, often coming with a 12V car plug. With the use of a buck converter for the Raspberry Pi I can run both the Pi and the CRT off 12V, and potentially even make the package portable.
Unfortunately, Claybrooke didn’t have the decency to supply the end-user with any video or audio input. The unit does however have a TV aerial plug and in the early 2000s when this unit was manufactured RF modulators were readily available from RadioShack.
Spending two to three times more than the price of the TV for an RF modulator just to interface with a Raspberry Pi didn’t sit well with me. There had to be another way, which meant that the next step was tearing it open.
WARNING: CRT screens operate with extremely high voltage and can cause serious injury and death. The information provided is intended for educational purposes only. Any actions taken based on the information provided you take at your own risk.
SAFELY DISCHARGING A CRT: Before working around a CRT it is imperative safely discharge the CRT. Information and instructions on how to safely discharge a CRT can be found online.
After removing a number of screws and safely discharging the CRT I was left to investigate the board. This TV, and many like it, are extremely similar and are based around a single TV IC.
In the Claybrooke’s case this IC was a CSC5151A. This IC is equivalent to the AN5151N and KA2915. I was able to download the datasheet for the AN5151N which contained the following block diagram and application circuit:
Pin 5 is listed as video out which would allow my to bypass the ICs video out and replace it with my own composite input. Before messing with any pins I searched online to see if anyone else had undertaken such a conversion with one of the aforementioned equivalent TV ICs. Maciej Witkowiak on Hackaday was one of several who had.
Following Witkowiak’s post I first determined that my board also used a shared ground starting with pin 21. However, where I differed was I wanted to avoid doing anything irreversible. Witkowiak cut the trace from pin 5 from the IC and then inserted their composite signal from a test point.
Since the CSC5151A was in a DIP package I was able to easily desolder pin 5 and lift it from its socket. I was then able to insert my own wire and solder it in place, thus bypassing pin 5 on the IC. This way, if I needed to use an RF modulator I could easily reinsert the pin without bodging anything. I did bodge in a wire on the bottom of the board into pin 21 for the composite input’s ground.
I connected the ground wire from pin 21 to the negative of a RCA screw terminal adapter and the wire from pin 5 to the positive. One lifted pin and two soldered wires later I had a composite input.
The Claybrooke provided an opportunity to use my Raspberry Pi B Rev 1 with it’s dedicated composite output and avoid soldering any additional headers on a newer Pi. While a modern LCD screen is in many ways preferable, there’s something uniquely cool about using a CRT.
An unavoidable downside is the risk of electrocution and death due to the CRTs high operating voltage, even here. Safely discharging a CRT isn’t difficult, but extreme caution must be taken when working around CRTs. Thankfully similar portable televisions exist that include a composite input, such as one made by GPX.