Wednesday, 22 April 2015

An inexpensive video RF modulator

    This is a description I wrote a few years ago of my RF modulator for displaying video on older TVs that don't have a composite video input. The Grundig telly mentioned and the cheap DVD player that prompted the build are both long gone, but the modulator is still a very useful piece of kit that gets used for a variety of video sources.

    My TV set is an ancient Grundig. It's a good telly for its age but nowadays any TV without a SCART or other AV socket on the back is getting rather difficult to connect to newer kit like my DVD player that didn't come with an RF output. No problem, I thought, I'll just plug the DVD into the SCART on the back of my VCR and feed the TV through that. At which point I came up against our friends the copyright owners. I don't think they like people plugging DVD players into VCRs! To stop people copying DVDs to tape, they incorporate an alternating peak white/peak black bar into the teletext lines on the video signal encoded on the DVD. These are the lines that normally sit out of sight above the screen on the TV, you'll only see them move past if your TV loses frame hold. The effect of this peak white/peak black cycling is to play havoc with the VCR's automatic level control, resulting in a signal from the VCR that flashes on and off and is unwatchable. As someone who is just using their VCR as an RF modulator I get caught in the crossfire.

    At this point I had several options. (1)Buy a new telly with a SCART socket, (2)Return my DVD player and buy one with an RF output, (3)Buy an RF modulator, or (4)build an RF modulator of my own. I chose (4) because I didn't have the cash for the other three and since it was Christmas I wouldn't have found a shop open to sell me one. I looked on the Web to see if anyone else had built one and couldn't find any information, so here to fill the gap are the details of my RF modulator.
I decided not to build my modulator from first principles. A simple design with a UHF cavity oscillator and simple sound and vision carrier and modulation circuits is not impossible to make using parts from a scrap TV set, but when so many set top devices already have a modulator built into them why bother? Instead I lifted the RF modulator from a scrap Salora satellite receiver I picked up at a radio rally.

    RF modulator modules usually conform to a fairly generic design. I have seen almost identical modules from different manufacturers in VCRs, set-top boxes and satellite receivers with a wide variety of brand names over the years. They are usually a shiny tinplate box a bit larger than a matchbox with PCB mounting pins protruding from the bottom and at least one co-axial RF socket on the side. Mine has 2 co-axial connectors, one for the antenna and one for the TV, a small switch to enable a test signal for tuning the TV and a 5 pin PCB header for signal and power. Since it came from a device for the British market it has a 6MHz FM sound carrier and outputs on UHF channel 36. The output channel is adjustable by means of a trimmer screw. If you live somewhere else in the world your local specs may be different, however the principle should be the same.

    Before I removed the module from the donor satellite receiver an element of signal tracing was necessary to work out which pin did what on the PCB header. I was fortunate that while the receiver I was using had a dead CPU its main functions were in working order so I was able to identify the power supply pins quickly by powering it up and using a multimeter. The video and audio pins were a little more difficult to trace, while it was pretty obvious which two pins were the signal pins a little tracing of PCB tracks to the video processor and the sound chips respectively was required to be certain which was which.

    There now follows a quick description of each pin on my modulator. If you do this, there is no guarantee that yours will be the same, however the generic nature of these modules means that they are usually similar. I have numbered the pins from left to right with the RF connectors on the top and to the left.

    Pin 1 Video. I don't know the spec of this input but it is very happy with the 1V peak to peak composite video from the phono socket on the back of the DVD player.
    Pin 2 Audio. This pin takes a line level audio input. My module is not a stereo device so this is mono only. As I run the audio through a hi-fi system this doesn't matter to me but I could simply connect both the left and right audio outputs from the DVD to this pin.
    Pin 3 +5V modulator power. This pin provides power to the modulator circuit.
    Pin 4 Ground. I connected this pin to the tinplate chassis of the module, which also formed the ground for my power supply circuit.
    Pin 5 +5V antenna passthrough power. I did not use this pin. In the satellite receiver it was powered by the standby power supply to provide an amplified passthrough from the antenna socket to the TV socket. Since I did not need this function I ignored it.

    The circuit diagram of my modulator is shown below.

    To power this modulator I built a simple 5 volt regulator using the ubiquitous 7805 IC. I simply soldered a TO220 heatsink to the module case and built the circuit around it. My choice of capacitor values was based on those I had to hand. I also included an LED to serve as a pilot light to indicate that the unit was turned on.

    The 7805 circuit was powered from a surplus 7.6v adapter originally designed for an Ericsson mobile phone. There are so many pieces of electronic equipment powered by small low voltage adapters these days that it should not be difficult to find a suitable surplus power supply. Any DC source between 6 and 9 volts should be suitable, though if you do not have a suitable candidate you can buy a universal power supply.

    The video and audio pins were simply connected to trailing phono sockets by short lengths of coaxial cable and the whole unit was mounted in a small plastic box with some hot glue.

    The performance of the completed modulator is the same as you would expect for the piece of equipment the module came from. Once the TV is conencted to the modulator output and tuned to the test signal the test switch can be turned off and signal applied to the phono sockets. An RF modulated signal is unlikely to deliver picture quality equivalent to a directly fed video signal but in this case the unit performed well and the quality when viewed on my TV was not noticeably different from that of off-air analogue broadcast signals.

    In conclusion, this unit provides a quick high quality RF modulator from a selection of junkbox parts.

Thursday, 16 April 2015

The sad state of the Raspberry Pi software ecosystem

    When looking at possible channels for a future Language Spy product last week, I took a look at the Raspberry Pi Store.  I've been a Pi enthusiast from the moment I heard about the project, indeed the Language Spy political corpus is driven by a pair of them.
    The Pi Store is an app store powered by IndieCity which is available both on the web and through an application included in the Raspbian Linux distribution that most people run on their Pi.
    I hadn't looked at the store since it was launched, so I was rather saddened to see it in something of a moribund state. Very little activity, an absence of the commercial software that was there when I'd last looked, not a channel that seemed to be going anywhere.
    Of course, you might ask why the Pi needs an app store. After all, Raspbian is a Linux distro, and thus has all the huge library of Linux software available for it, at least all that will compile and run on the Pi's limited hardware. And in a sense you'd be right, in that a few seconds with apt-get can satisfy almost your every software need.
    But the success of a machine like the Pi depends on more than just using an operating system with a much wider support. Platforms succeed when they create an ecosystem around them, and while the Pi has been very successful at creating a hardware ecosystem the failure of the Pi Store serves to highlight the sad state of its software ecosystem.
    In the last couple of decades working in software companies it has been my observation that the most successful new platforms are those with the lowest barriers to development. In the 1990s the PlayStation trounced the cartridge consoles by not requiring developers to stump up for a huge inventory of plastic bricks for example.
    In a way one strength of the Pi - its Linux OS - is also its weakness when it comes to the Pi Store. There are so many different paths to Linux development that the Pi Store lacks that crucial low barrier to entry offered by a simple choice. What the Pi Store needs is an "official" way to write code for it. A straightforward community-supported development path encapsulated in a single download from the store which contains everything needed to publish. In fact I'd go further, what it needs is two such routes, one for simple apps and one for more demanding apps, roughly analogous to a framework like Apache Cordova and Java respectively in the Android world. Maybe Cordova on Qt and Qt itself would fit the bill.
    Meanwhile it's no use saying "Rubbish, everyone can just use [insert your pet 1337 dev environment here]!" when the people who are slowly becoming advanced users and wanting to code on their Pis might not have the required technical expertise to master all its nuances straight away.
    In the way thus described the Pi Store could become a channel with a low barrier to entry. This is not to say that the "official" dev path need be the only one, more of a "You can code how you like for the store but here's a straightforward way to do it".
    I won't be developing that Language Spy product first for the Pi Store as it stands, it would not make sense when other channels will give me a much better airing. The Pi remains a platform with some potential for a developer like me, but until some serious attention is paid to its app store I don't see it gathering its own software ecosystem.
    I don't know about you, but as a Pi enthusiast I think that's a shame.

Wednesday, 1 April 2015

Automotive manifesto

    Cars are crap, these days.

    Something has to be wrong, for me to say that. I'm a lifelong motor enthusiast, petrolhead and engineer. Cars are on paper at least, better than they've ever been. Their engines last for hundreds of thousands of miles, they don't rust, and they all handle pretty well perfectly.

    So why do I say that cars are crap these days?

    A few weeks ago I sat in a new car from a global manufacturer. It's nothing special, most cars from the last decade are to a greater or lesser extent similar. It's got an extremely advanced engine that will return MPG figures impossible a generation ago, it has a galvanised body, and it'll reliably haul a family of four all day in supreme comfort at autobahn speeds.

    Yet I am fairly certain that it and nearly all of its model will be headed for the crusher within a decade. Why? Driving it is not the experience we'd expect from a car made a decade or more ago, instead it's a software experience. It has a digital dash whose instruments were as far as I could see mostly on a TFT screen. When you turn the headlights on a switch doesn't complete a circuit to the light, instead its computer sends a signal to the microcontroller in the light to turn on. Same with all the other controls, even the handbrake. Yes, the handbrake, that thing you rely on to stop the car rolling away down a hill, is no longer a cable but a computer

    I looked at that car and saw an engineering masterpiece. I'm an electronic engineer, my dad's a blacksmith and I've been around bits of cars all my life. I know how all this stuff works, in intricate detail.

    But I also looked at that car and saw something I wouldn't touch with a barge-pole. I know that within that car is something that won't live up to the manufacturer's hard-won reputation for reliability. It may be that digital dash, it may be the microcontroller in the headlight, the one in the brakes, the throttle, or even the network of data cables that carry all that info around the car's systems, but something is going to fail on that car that won't be fixable without telephone number money, and then the car will be junk.

    The problem is of course that the manufacturer couldn't care less. The person who owns the car when whatever piece of techno-crap sends it to the scrapheap won't be the person who drove it off the forecourt, because people who are prepared to take the hit of new car depreciation usually do so because they are so desperate to always drive a new car that the money doesn't matter. So the people who keep the manufacturer in business simply don't care about its built-in obsolescence, therefore the manufacturer doesn't care about it either. (I am a rare exception, I've owned my 2001 car from new)

    This makes no sense. It's an oft-quoted line, that more energy is used in the manufacture of a car than in its lifetime of driving. Therefore if we can make cars whose engines and bodywork last forever it is irresponsible to throw them away before they are worn out. No, your fancy hybrid is about as green as a coal fired power station if it only lasts a few years.

    I can not in good conscience participate in this scheme of car ownership. On an environmental level sure, but also as an engineer, I don't think I want to buy something that's designed to be so unnecessarily complex as to be unfixable, it's just wrong.

    So here's my automotive manifesto.

    I will buy a car that has in every instance only the technology that is needed to perform the task in hand, not more than is needed. If all that is needed to turn my headlight on is a switch and a copper wire than I do not need a CAN bus and two microprocessors to do it. I am quite happy to pay for the copper wire and carry the marginal extra weight it brings to the car.

    I will buy a car that has high technology where it is needed and where its use makes sense. For example a microprocessor is necessary to control my engine or my anti-lock brakes, but is not necessary to provide basic instrumentation.

    I will not buy a car that uses high technology to ensure early obsolescence or to lock-in to a dealer network. If your digital dash costs a four figure sum to replace, or if only your dealer can perform service tasks, then you will not see my money and neither will your dealer.

    If I can not buy a car that meets these simple requirements then I will not spend a lot of money for a car made in a European, American or Japanese factory. I will simply spend as little as possible on the cheapest pile of Pacific-rim crap-on-wheels I can find, and bin it when it dies. If I do that then I'll have wasted a lot less money than I would binning a fancy car with a dead digital dash.

    I'm just one person. My consumer choices don't figure on the radar of a car manufacturer. But I know the automotive frustrations of one can also be the frustrations of many, as for years I kept the Austin Rover faith as they kept churning out frankly awful cars. Where are those Austin Rover factories now? Mostly housing estates, retail, and industrial parks.

    I know I won't be alone in walking onto the forecourt of the first budget Chinese carmaker to arrive in my town. Who knows, perhaps it'll occupy the site of the factory where they made that brand new car I mentioned earlier.