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You don’t have a computer handy . . . so, How do you play music tracks on USB Sticks or SD/MMC Cards? by Ross Tester Do you ever wish you could simply play music tracks that you’ve saved on a USB stick or memory card? We had a particular reason for developing this project but it could easily be incorporated into your home hifi system for real convenience! T he “Quizzical” game adjudicator (described in SILICON CHIP in September 2011) included a module designed to play MP3 music files – we used it to provide a different sound for each quiz contestant, one which could be changed as required. As often happens, this project started us thinking about another possible use for the module – that of playing music files “on demand” from an SD or MMC card, USB stick, etc, without resorting to playing them through a PC. First, a bit of background. The idea for this came from a colleague who manages a public hall, often used for wedding receptions, 21st birthdays and even corporate and public meetings. More often than not (especially for receptions and birthdays) those using the venue wanted to play music files through the hall’s PA system. If they provided them on an MP3 player with headphone output, no drama – the PA had been rigged with a “line in” terminated in a 3.5mm plug. But just as often, someone would produce a USB stick (or sometimes a memory card) and ask if they could play the music they’d stored on those. The manager usually obliged by plugging in his laptop computer and using that to read the stick or card. But apart from the security risk of leaving his laptop when he wasn’t there, it 84  Silicon Chip was a lot of mucking around. It also meant he couldn’t use his laptop that day or evening! He’d seen the Quizzical and asked if there was some way its MP3 ability could be adapted to provide this “service”. And then we thought, why not go one step further? If you mounted a plate containing one of these modules on (or even in) a convenient wall and connected it to your hifi system or home theatre amplifier, you’d have five-second plug-in convenience if you ever wanted to play music you’d previously saved on a USB or SD! And a lot of people want to do exactly that! Not exactly practical On closer examination we decided the module used in the Quizzical, a TDB380 from Tenda Electronics, was not really suitable. Sure, it would read the files stored on an SD card – but it needed some “smarts” (eg, the rest of the Quizzical!) in order to select the right track(s) and so on. Not only that, it didn’t have other features that we really wanted: a USB interface, for instance, nor would it take an audio input if someone did bring along their MP3 player (or even The three USB/SD/Audio modules we obtained from Tenda Electronics. All have the same function but the size differs. siliconchip.com.au Here’s what we did with two of the three modules. At left, the TD898 module fitted to a blank power point plate. It has the advantage of a front-mounted “audio in” socket. The hole in the plate is for an IR receiver (all come with remote controls). At right is the TD896 module mounted in a small box – it’s our fully portable version. We chose this module because of its overall small size. their own cassette recorder). The TDB380 would need quite a lot of work and additional circuitry to bring it up to the mark. Scratch that idea. But wait . . . they have more! Then we found that Tenda Electronics had several other modules which appeared to do exactly what we wanted – not only that, these modules had the “smarts” built in to select tracks, fast forward and reverse, play and pause, even volume controls (handy for selecting different levels for background music and dance music). Some also had LCD displays to tell you what was happening. All even had small built-in audio amplifiers, though these would not be needed for our original application. Another bonus: they came with remote controls, although given the penchant for hall hirers to walk off with these in their pockets (as they do with the door keys!), this might be regarded as a mixed blessing. . . The best part is the modules were cheap as chips – the whole module sold for less than we could have purchased just the USB and card readers here in Australia. Oh, did we forget to mention? Tenda Electronics is, like the vast majority of electronics suppliers these days, in China. More on that anon. siliconchip.com.au We reasoned that we could not only provide what was needed pretty-much “off the shelf” merely by providing appropriate connections, we might also have the germ of another simple SILICON CHIP project – a fully portable USB/SD/MMC/audio player. And this could even take advantage of the inbuilt amplifiers to give either headphone or speaker outputs. So this little feature is the outcome. It’s not a constructional project because 95% of the work is already done for you. Basically, all we are doing is showing you how to connect to the modules and some mounting ideas. What data? Unfortunately, the information on Tenda’s website (like arguably the majority of Chinese manufacturers!) leaves a lot to be desired. Not only is it out of date (there are differences between the current modules and the website) the information is scant, to say the least. Which module? Not knowing exactly what we wanted, we ordered three different Tenda modules from the variety on offer. It appeared to us that any one of them would be capable of the tasks required and that proved to be case – although one proved to be the best of the lot. The modules we ordered were the Tenda models TD866, TD896 and TD898. The first two have the LCD readouts mentioned earlier; the last one does not but it does sport a front panel 3.5mm audio input socket. While the first two provide audio inputs on the PCB, they need to be connected to. In the end, we decided the TD898 would be the best for the hall, despite not having an LCD readout. For our portable player, we decided on the TD896 – mainly due to its smaller size. You can order these modules direct from Tenda (www.tendaelectronics. com) but they will set you back $50 each by the time you include freight. Or you can order the TD896 or TD898 modules from SILICON CHIP for $33.00 each plus $10 p&p. Prices include GST. (parts<at>siliconchip.com.au) JST connectors Unfortunately, all three modules use JST (Japan Solderless Terminals) connectors, which look like a miniature header socket (see photos). These connectors are often used in computers and computer peripherals. The leads which mate to these connectors might be solderless when manufactured but we found they pulled apart too easily when simply crimped, so we used a “belt’n’braces” January 2012  85 AUDIO R      GND OUT L AUDIO R      GND IN L Here are same-size top and bottom views of the TD896 module showing connections – the top side if you wish to use JST connectors and the bottom side if you wish RIGHT SPEAKER to solder direct to the LEFT pads underneath. SPEAKER The speaker connections can be ignored if you don’t want to use headphones + DC or speakers. AUDIO R      GND IN L AUDIO R      GND OUT L – DC + IN RIGHT SPEAKER LEFT SPEAKER – IN approach and (carefully!) soldered the wires after we’d crimped them. We used strands of ribbon cable to make up the connectors. Strictly speaking the audio input and the output to the amplifier should be shielded cable but for this length, ribbon cable is OK and a whole lot easier to handle. We’ve got to say that making up these connectors has to be one of the most fiddly tasks ever devised – even under a large magnifying glass and bright light it was a real chore. So much so that with 20/20 hindsight, we’d either solder direct to the PCB (on the back of the JST connector) or we’d buy ready-made JST header leads. That’s not the easiest thing to do either – they’re not something you can walk into your local lolly store and buy. It’s also not particularly easy to buy the bits to make the leads up. So we have decided to import limited quantities of these and also make them available through the SILICON CHIP parts shop – the 2-wire JST cables (100mm long, bare one end) are $3.45 each (inc GST) and the 3-wire are $4.50 each (inc GST) – all prices plus postage. (they seem to be 38 or 45mm deep). We decided on an Altronics H-0302 Sealed ABS Enclosure which measures 85 (w) x 80 (d) x 55mm (h) – the width and height are just enough. We happened to use one with a clear polycarbonate lid; this is not a requirement and the standard grey lid would be fine. The first step in construction was to mount the module on the lid – this requires a little surgery to the lid. Exact position isn’t critical but make sure it is centred left to right. We used a small cutting wheel mounted on a Dremel-type drill – it might not be the neatest job in history but if you get it right, the cutout will be Portable player Our first “project” using these modules – actually the TD896 – is a semi-portable music player. It’s small enough to go anywhere but needs a 3.7V (or 5V) DC power supply to operate. We considered making it batteryoperated for complete portability but reasoned that most applications – at least in our experience – would have access to power. First decision was the case into which we mounted the module. It’s reasonably small at 75 x 55mm but the deciding factor is the depth – at 50mm it’s too deep to fit into most small cases 86  Silicon Chip completely hidden by the front panel. Take “baby steps” – keep enlarging the cutout a millimetre or so at a time until the module just fits through. The supplied self-adhesive label should be left until the very last, just in case you need to take the module out again (the label will cover the screws when secured in place). Next, drill the holes in the bottom of the case for your power socket (8mm), RCA output sockets (9mm each) and the earphone/speaker 3.5mm socket (7mm). We placed the power socket on the bottom end of the box and the three output sockets on the top but you can place them where you want. Taking note of the polarity of the power JST connector, solder the power socket to a 2-pin JST lead, then use two more 3-pin JST leads to connect to the audio output sockets (note which pin is ground on the JST sockets; the two audio output socket grounds connect together to this wire). Finally, connect a 2-pin JST connector to the earphone/speaker socket (again, centre pin is ground). Now plug the JST connectors into their appropriate sockets on the PCB and you’re just about ready to rock and roll. Power supply And here’s how it fits into the Altronics H-0302 box. The DC input socket is in the foreground, while the audio input (3.5mm socket) and audio output (2 x RCA sockets) are on the rear wall. Otherwise everything mounts onto the front panel. The Tenda literature says either 3.7V or 5V DC – we’ve taken a punt on 3.7V because we found a label that said so! Until proven otherwise, we’ll stick with that! Fortunately, 3.7V power supplies are quite common these days – many mobile phones use them and given the fact that there are several million more mobile phones in Australia than people, we’re assuming there will be a fair number of surplus power supplies as well. Even if you have to buy one, siliconchip.com.au AUDIO OUT R GND L LEFT SPEAKER DC IN – + it’s not likely to cost a King’s ransom! Just watch the polarity when you connect it up – it’s most usual to have the centre pin positive but we’ve certainly seen exceptions. The PCB is clearly marked. The original request – amplifier music input Connections, JST leads etc are similar to the portable player, except that we ignore the on-board stereo amplifier. Of course, if you want to use the amplifier for you application, go right ahead! After dithering about with various mounting arrangements for a couple of weeks, we finally hit on one which we think makes sense. The difficulty, once again, was finding something deep enough which could be mounted on a wall. We were restricted in our options because the unit needed to be mounted on a solid masonry wall skinned by Gyprock. Hence the module had to be mounted proud of the wall with enough depth to suit. (The Tenda TD898 module requires 43mm clearance). We actually used two products to – + DC IN RIGHT SPEAKER The TD898 module does not have a JST connector on the front for audio out – you need to solder to the appropriate pads on the rear of the board. Fortunately, all pads are quite clearly marked. DC in can be via a front JST connector or it too can be soldered to the pads. get the depth needed. First, a standard 37mm-deep power point mounting block (HPM 140P), on top of which we mounted an 11mm-deep power point mounting plate from an HPM XL770/0 plate and cover kit. Together, that gives us 48mm depth. We could have mounted the Tenda module directly on the plate but it looks rather ugly. So the module itself mounts on the blank cover plate which comes with the HPM XL770/0. The beauty of this particular blank plate is that it clips onto the mounting plate – no screws required. (While we used HPM, there’s nothing to stop you using an equivalent product in another brand eg, Clipsal, etc). Naturally, you’ll require a cutout in both the mounting plate and the blank plate to suit the module – our cutout was 87 x 33mm right in the centre. This creates something of a problem – the lugs for screwing the mounting plate to the block have to be removed to get the module to fit. We overcame this by using a couple of self-tapping screws though the outer pair of holes left after cutting the lugs out. Again, these are completely covered once the plate housing the module is snapped into place. Termination As the wires to the JST connectors are quite flimsy (they’re only ribbon cable, after all), we wanted to make a more robust connection for both power and audio out (to amplifier). To this end, we cut a scrap of old PCB to an appropriate shape and mounted a 5-way mini terminal block on it – two for power, three for audio [L, GND & R). This arrangement suited us but you might come up with some other way of protecting the fine ribbon cable and connector. Connecting to your amplifier If you are running into a stereo amplifier, simply connect the left and right “audio out” to an “Aux” input via twin shielded cable. If you are running into a PA or similar (mono) power amplifier, you need to combine the left and right channels into a single mono input. Ideally, there should be some resistance – say 1k  – in each line to isolate them from each other but we’ve never had a problem shorting left and right to mix them. Mounting within the wall The TD898 module mounted on the wall and ready for action! siliconchip.com.au Because we are using standard power outlet fittings, it follows that if you have a standard stud/Gyprock wall, you could mount the module almost entirely within the wall cavity for a less obtrusive, much neater finish. For example, as long as there is sufficient space in the cavity you could eliminate the 140P mounting block and simply have the XL770/0 block fixed to the wall using a power outlet support clip or plate. Then your USB/SD module, mounted on its blank plate, would simply clip into place on that block. SC January 2012  87