Re-imagining The Casio Pocket Television TV-470Posted: March 25, 2015
Ever since I watched Alexander Armstrong watching a Sinclair pocket TV in Micromen, I have been unable to shake the idea of a pocket video player. I used to own a Casio pocket TV back in the 90s; I’d take it to school, on car journeys and sometimes hide under the duvet at night, hoping to catch a late night horror film. It was all a bit of fun really for me as a kid, catching Star Trek on my tiny Casio was something of a novelty. But as time went by, the little device got used less and less. The battery life was never anything amazing, lasting a couple of hours before going flat, but something about watching Micromen had me hooked on the idea and I couldn’t shake the need to take a crack at it…
Best Laid Plans
Originally my plan had been to buy a second hand Sinclair Pocket Television and hack it in to a portable video player. Perhaps even convert it to receive a digital signal along the way. I soon realised this was an unrealistic goal, as even the smallest Freeview receiver came in a box requiring an additional power supply. I’d be restricted to the size of the Sinclair’s tiny case, the electronics would never fit inside. Going back to the drawing board, it dawned on me that I still owned my old Casio TV-470. So I dug it out from its dusty corner and powered it up one final time. As analog was shut down quite some time ago, all i got was static.
So with a final farewell, I removed the back and took out the guts, casting them to the eternal dustbin in the sky. Next came the more complicated part, finding a suitable device that was not only small enough to go inside the empty case, but work with it’s existing buttons.
Simple & Effective
I knew early on that my best bet was to go with a cheap Mp4 player, the sort that can usually be bought off Ebay for next to nothing. I had two main requirements that needed to be met for the project to go ahead.
- Hardware buttons – So micro switches could be used behind the Casio’s plastic buttons, thus allowing the overall appearance of the device to remained unchanged. The channel buttons would act as ‘Forward’ and ‘Back’ navigation, ‘Select’ would act as a play / enter button and the power switch on the side would continue to work as it had before.
- Screen Size – The Casio was originally fitted with a 2.2” inch screen, and as I couldn’t find any players using a screen that size, I would need to compromise. If I used a screen to small or too large, I would face problems with it looking odd behind the Casio’s front fascia.
Tevion MP4 Player
Fitted with hardware push buttons, a 1.8″ colour LCD screen and an internal speaker, the Tevion seemed ideal from the job at hand. The player also had a switch to turn it on and off, this was great as it meant I could utilise the Casio’s existing power switch to turn the player on an off. With all these positive points, there has to be a down side and the Tevion did have one draw back, it had more buttons than the TV-470 case was fitted with. This meant I would have to alter the case to some how accommodate two extra buttons. Initially, I considered turning the contrast and volume dials on the side of the unit in to buttons. I’d do this simply by cutting them in half and gluing them on top of the micro switches I planned to use. Superficially they would still look like dials, only when you pressed them would it give the game away.
Sadly I realised this wouldn’t work as there simply wasn’t enough room in the Casio to house the buttons and the dials. In addition to that, I couldn’t figure out a durable means of gluing the half cut dials to the switches. An attempt with superglue almost ruined one of the micro switches after it leaked inside the housing of the switch and gummed it all up. In the end I had to accept that I couldn’t keep the tiny TV looking 100% original, the buttons had to be accessible for the device to work. This meant cutting out two holes where the dials had once been. I mounted the micro switches to a tiny piece of bread board that I had prepared and glued it behind the inside of the case, leaving both switches laying flush to the side of the Casio case. The method not only proved to be the most straight forward, but also didn’t turn out as bad as I’d expected. The overall look of the little telly remained pretty authentic looking.
Using another bread board, I aligned a set of three switches behind the front fascia of the case. This meant that the front buttons were pressed, they would trigger one of switches behind. I hooked up the three switches to the MP4 players controller board. Select went to select / enter on the player and channel up and down, now acted as reverse and forward. So if I needed to fast forward a video, I only needed to press the channel up button and the video would skip forward. The additional side buttons controlled the Play and Volume functions respectively.
Getting the power switch working proved another challenge, as the plastic switch was molded to work with the Casio’s original motherboard. I wanted to keep the switch authentic, so taking a chance, I cut the switch out of the original PCB. Extending a series of wires from the switch to the Tevion PCB, I was able to turn the board off using the original switch. Next came positioning it so that it worked correctly with the plastic switch on the outside of the case. This was something of a nightmare, especially when working with a hot glue gun. One of the key reasons I’d chosen this particular player was because it didn’t have a touch sensitive scroll wheel. I knew with relative confidence that I would be able to hack in to the hardware buttons or at least rewire them. In retrospect I might have been able to get away with using one with a scroll wheel, however many of those players also come with a rotating screens. Something which would simply not work in the little television.
Power I Need More Power!
Something I really should have thought about before undertaking this project was how I would project sound from the device. The headphone jack is all fine and good for personal headphones, but it’s a weak signal and not strong enough to power a loud speaker. The Tevion did come with an internal speaker but it was lousy and quiet. In fact the only way I was able to get anything to play through it at a decent volume to listen to, was by increasing the gain on my videos while I was converting them to AMV, then when I copied them over to the device, I was finally able to hear something out of the weak speaker. There was however a drawback, increasing the gain also increased the level of noise, resulting in some rather loud hissing in the background.
I considered using a piezo transducer, but even one rated at 1.25w was too much for the output from the Tevion. I needed something with much lower power demands and after finding a 0.35w speaker on Ebay, I sat back and waited patiently for it to arrive, hoping this would finally solve my problems. In the mean time while out shopping, I stumbled upon a small speaker in Poundland. It was designed specifically for hooking in to the headphone jack of a phone or CD player.
If this device could run off the meager output of a 3.5mm jack, then surely, I figured, it would run off the Tevion’s internal sound port just fine. After dismantling the unit, I found at it’s core was a 0.25w 29mm speaker wired directly to a 3.5mm jack. A pretty simply circuit, but hey, we like simple. A quick snip of wires and I had the speaker soldered in and hooked up to the Tevion’s PCB. Selecting a movie, I held my breath expecting it to either not work, or be very quiet. Because of how quiet everything had played up until this point, I had the volume set to 30, which in hindsight was probably a bad idea. The new speaker blasted out sound at a crazy level, which I didn’t even think the board was capable of. Huzzah! Finally I had my answer, a .25w speaker was what I needed to get the device to playback with acceptable sound. At 29mm the new speaker not only dwarfed the one that came with the Tevion but also the Casio’s original 20mm internal driver. As a compromise I installed the new speaker in to the now defunct battery compartment, using a piece of sponge to stop it from vibrating against the inside the case. This would be a temporary solution until I found something smaller. If I could find a suitably rated 20mm speaker, I could place it exactly where the Casio’s original speaker had been.
The quest to sort out the sound for this little television has certainly been an interesting one. I’d thought having found the Poundland .25w speaker everything was finally settled. Then while eating pizza and watching a movie at a friends, I found myself being handed something new to try. A .25w speaker that you can attach to pretty much any surface and turn it in to an active speaker.
The Tevion has some cool features, it’s a video player, portable radio, ebook reader, it also comes with some mini games. The only function I’m bothered about is the video playback. What can it play and how well can it play it? Having owned similar Chinese mp4 players in the past, I knew it would be unlikely that I would get the Tevion to play AVI’s or Mpeg4 videos. Most of these inexpensive players use MTV or AMV video formats. The AMV file format is something commonly seen on Chinese players and I’m not sure exactly why that its. Possibly because it requires the least processing power. More expensive brands such as Archos, Sony, Creative and Apple utilise more commonly found formats such as AVI, Mpeg. and MP4. AMV in itself is not a terrible bad format, it’s just rather old and rarely found on modern video converters. Which makes finding software that works in Windows 7, something of a challenge. Luckily there are one or two programs which will get the job done.
Videos converted in to AMV will never be anything amazing, playing back at 8 to 16 fps, the picture quality is comparable with that of a 140bp Youtube video. But when you realise this is being played back on a 1.8“ screen, is anyone really going to notice mpeg artifacts? In it’s original form the Casio TV was at the mercy of the weather, bad atmospherics, passing under a bridge or dropping in to a valley could all lead to poor picture quality. With that in mind, having the odd artifact or pixelation from a converted video really doesn’t seem that much of a big deal. AMV might not be as good as other video formats, but one thing which is does have in aces is small file size. A 60 minute video can take up as little room as 230mb, which really isn’t bad when I have 2GB of memory to play with.
This has been a cracking little project which I’ve really enjoyed working on. The tiny TV-470 is back in use and working as a perfectly good video player allowing me to watch old black and white movies, cartoons and what ever else I might fancy sticking on it. It’s also great to have when your laid up in bed feeling rough. Ok it will never replace a phone or a tablet, but it does mean I’m not draining the battery on those devices as much as I would. Plus there is something kinda fun about watching old movies back on the TV-470. Now if I can just figure out how the Tevion uses the headphones as an antenna, I might be able to reuse the original aerial for a real purpose.
Till next time, keep on geeking!