Sanyo LMU-TK12AT touch screen LCD monitor with OSD setup

Lost your OSD controller? Do not despair...

Recently a mate gave me a Sanyo LMU-TK12AT monitor which he had found in a skip and thought would appeal to my habit of collecting technological junk. He was right. I wasn't initially interested in it but once I realised it had a touch screen I began to think of applications for it. I could stick it on the wall as an electronic picture frame, using the touch screen to select which picture to display from a library on a server. Or I could make it into an electronic dashboard and control panel for a motorcycle. Excellent.

But first I had to find some data on it. It had an RS232 connector which I presumed was for the touch screen output, but it didn't say what baud rate it used, whether you could get away with a three-wire cable, or any other useful stuff. Even more enigmatically, it had a USB connector - an A connector, not a B - labelled "OSD". What on earth was this supposed to do? Some intensive googling was called for. Rather more intensive than I would have liked. Lots of results turned out to be not downloadable files but lists of files on some CD that you could send off for, or some wanker listing the contents of some directory on his computer as a text file rather than a virtual directory (why the fuck do people do this, what's the point?), or some other species of wanker requiring a registration before I could download stuff with no way to be sure I could delete all records of the registration once I had finished downloading.

Finally I found a useful Latvian supplier who had a comprehensive user manual for download. This revealed that the RS232 used any standard rate between 1200 and 19200 baud, on a five-wire cable, 7 or 8 data bits, 1 or 2 stop bits, none/odd/even parity... How do you set which it uses? Presumably using this "OSD" thing... Although it uses a USB connector, it's not a USB port, it's just four DC signals which you short to ground to activate "Menu", "Select", "Up" and "Down" functions on the On-Screen Display. The idea is that having set up the monitor via the On-Screen Display you can unplug the control buttons and take them away with you to stop people fucking about with the settings. And the user manual even gives you the pinout of the connector, reproduced below along with the corresponding wire colours in a standard USB cable:

 Pin   Function   Colour 
 1   Menu   Red 
 2   Select   White 
 3   Down   Green 
 4   Up   Black 
 Shield   Ground   - 

The pinout of a USB A plug, looking into the open end of the plug, is:

USB A plug pinout

The shield, of course, is connected to the metal shell of the plug.

This provides enough information to cut the B plug off a USB cable and connect the cable to four push buttons mounted on a scrap of Veroboard, thus allowing me to replicate the OSD controller which my mate had either not found in the skip or not realised the significance of. Note that it uses the shield as a separate conductor, ie. it's effectively using the USB cable as a five-wire cable rather than a shielded four-wire cable.

One final frig-about was required before I could fire it up. It runs off an external 12VDC power supply (the original is rated at 2.6A, though the consumption of the monitor is only 20W), and the power supply connector was some weird-ass thing that looked like it accepted something like a miniature phono plug. Fortunately the pinout of the socket was pretty close to what passes for a standard on DC power connectors, so I was able to unsolder it from the PCB and replace it with a standard 2.5mm DC power connector without having to mutilate things too much.

Does it work? Well, unfortunately, I don't know yet. To my dismay, I discovered that contrary to my expectations I did not have a spare VGA cable to connect it to a signal source. How I come to be in this parlous situation I know not, but there it is. I also have a nasty feeling that I've run out of 9-pin D connectors to make up a five-wire RS232 cable (all my existing RS232 stuff is three-wire). But anyway, without a signal source connected, the monitor goes into standby mode and apparently will not listen to the OSD controller when in standby. I've made the basic electrical checks - the four signal lines are definitely all inputs, connected to +5V via 330k pullups, and pressing the buttons takes them to 0V, but the monitor won't listen. Further updates will be posted once I've got hold of a VGA cable and can tell whether it's just not responding because it's in standby or whether there's something freaky about the OSD input for which my simple push button array is not providing the appropriate signal. I do at least get stuff on the screen telling me the monitor's going into standby mode because it's got no signal, so it can't be completely knackered.

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