I’ve been meaning to set up something to generate a testcard via composite video for a while and, as is typical of me the ideal solution was sitting there in a BATC magazine on my bookshelf. CQ-TV No 270 has the details of one such setup using a Raspberry Pi Zero. I don’t have one of those and Pi systems are hard to come by these days but surprisingly I had a 3B not doing anything. Software downloaded, 4-way jack to RCA plugged in and connected to a TV and, nothing. Well, a buzz. Checked the cable, all ok. Checked what the Pi wants…
…why does the Pi have to have the connections different from what appears to be a standard hi-fi 4-way to RCA lead? Or, rather, why does the hi-fi 4-way lead I have have to have different connections? Grumble.
Ok. I wanted to test this seeing I had it all sitting in one of the bedrooms attached to a TV. Stripping down a 4-way jack lead that I never needed and which was far too short to be of use I made a lead. It would last probably half a second in normal use but worked sufficiently well to prove the setup.
It is of course a waste of a ‘whole’ 3B, but until I get a Zero this at least lets me push a testcard out when I need one. The alternative has been to use the rather clunky Sandisk device that can present an SD card or other media to an a/v output, as used in my first 5.6GHz setup https://m0rvb.uk/index.php/2021/05/22/5-6ghz-experiments/ – this way is a whole lot neater!
It really is taking me far too long to get this sorted out. But, finally some progress has been made… at least I now have a decent case and the screen mounted. So far, there is very little else in the case other than the Lime and Pluto, the screen, the Pi and a 12V to 5V converter. But at least there’s plenty of space to add all the other necessary bits and pieces.
The screen was the most awkward thing to mount as it is designed to fit easily into a plastic surround with the Pi directly behind. For that, the 4 mounting screws fit directly to the case. But here I want it in the front panel. My rather less than elegant solution was to get some 1/4″ square aluminium bar, make holes for 4 M3 nuts and bolts and tighten these to become studs – these are in the horizontal pieces as shown in the pic. These were then epoxy glued to the front panel. Two more bars then take the screen, with spacers so the screen isn’t pulled back too much when tightening.
Anyway, elegant or not you can’t see it from the front! Still to go on yet are the three push buttons and encoder / tuning wheel for the Langstone transceiver part of the kit. As for the rest, well, one thing at a time! But anyway it works… as shown by yet another successful 6″ transmission to the Winterhill box sat on top!
After finding the dead LCD screen that was to be a 5.6GHz ATV receiver it also turned out that the 7″ Pi screen on my Portsdown setup had similarly died – just white lines on the screen. No amount of stripping, reassembling and general fiddling fixed it. A new screen did.
Anyway, I now have a Winterhill receiver. This came from a fellow ham and saved me building one. As is usual with any new box one absolutely must try it right away, which is how I discovered the bust screen on the Portsdown. After that was replaced I successfully sent a test card 40 inches across the desk! Small steps… and at least the Winterhill is in a nice box unlike my Portsdown which is still waiting for a suitably sized case – why is it all the nice metal boxes are a few mm lower than the 7″ display needs. Huh.