How easy can it be to build a TV Tuner?
Quite, if you design it like Twinhan did.
Twinhan (also known as VisionPlus) was a big company making digital TV tuners back when digital TV tuners were new. The VP-7045A/VP-7046 tuners (known as Alpha and Magicbox II) were my favourite tuners, as they were sensitive and fairly compatible. Running Windows 2000 Professional, the fact they came with WDM drivers meant that they worked, whereas other tuners (especially the slim ones) of the day had horrid sensitivity and driver issues.
Of course, the VP-7045A/7046 were not free of driver trouble – they caused BSODs every so often, and new versions of software often broke compatibility. But what is interesting is the support for this tuner – it’s well supported under Linux, and with some effort, can be made to work on machines spanning from Windows 2000 Professional to Windows 7 x64 edition!
Not all of their tuners were great – I’ve tried their Satellite tuner too, which has a hardware demultiplexer which causes a heap of compatibility issues – it shows that simple can be better. Later in this post, you can see just how simple these terrestrial tuners were.
It’s my most long-lived TV tuner – I liked it so much that I have three of them. But rather unexpectedly, Twinhan’s website has been down for a while – and there’s not much about them left around. From what I have been told, they have been bought out by Azurewave and the latest drivers can be had from here.
The problem is that the application provided there does not work – in fact, an older version that I have (DigitalTV 3.4 Build 11) does work when given some persuasion – i.e. manually install driver first, run the application with administrative rights. In the case that doesn’t work, the tuner is still useful as you can use this simple application from Twinhan (THTSCapture_20070521) to capture a complete transponder transport stream so that you can analyse and demultiplex it later. Or you can use it under Linux!
First up is the older Twinhan Magicbox II. This one cost me about $120, and I have two of them. It’s fairly bulky, hand-sized, but quite light. It comes with a stand too. The bottom label gives you a hint that it’s VisionPlus (by the VP naming nomenclature).
So, I’ve disassembled this one before, so I know where the screws are. Undoing them, and the two clips in the top, one can open this up like a clamshell – like so:
Look at all that empty space. In fact, the other side of the PCB is pretty much bare – but on this side, you can see the USB connector, crystal, bypass capacuitors and the Cypress EZ-USB interface. This chip is a jack of all trades – it will pretty much let you bit bang and or interface any parallel or serial digital stream to USB, in fact, everything from IDE to USB bridges and even the Saleae Logic Analyser is built upon something this simple.
All they’ve done is interface an IR receiver and the Samsung NIM (Network Interface Module) to the EZ-USB interface to make a TV Tuner. The NIM itself has the front end tuner, filter, and demodulator and just puts out a parallel stream of bits which represent the data in the packets on the air, while taking some commands (possibly via I2C/SPI) for tuning.
So, it’s no surprise that there is this unit …
This one’s about 1/3rd of the size of the unit above, and I have one of them. This uses a common driver – surprise surprise, it’s basically the same unit!
You can tell, the model number is fairly similar. Instead of using a USB B connector, it uses a USB A connector similar to USB memory sticks.
Again, same parts, different PCB!
And on the underside it’s pretty much the same NIM.
So why is this a great thing? It means a lot of the work is done in software – this allowed the tuner to have demultiplexers based in software, so that the tuner could evolve from WDM drivers up to BDA drivers, and allow us to record a whole transponder. It also allows you to use the tuner with different tuner software – e.g. TSReader, ProgDVB, AltDVB. And it means that these tuners, over 10 years old, are still useful today!