TV with MStar IC **Now with added touch screen goodness**

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TV with MStar IC **Now with added touch screen goodness**

Postby nes » July 23rd, 2012, 2:17 pm

Hello. I recently picked up a 3.5" composite video input LCD monitor from the bay of E for use in a project.


The image quality turns out to be pretty good and I was pleasantly surprised to find out that the panel its fitted with has a resistive touch screen, though it's not connected to anything. (The panel is marked PT035TN24, GP Innolux Display.)

The monitor is fitted with buttons and an OSD which gives rudimentary control over brightness, contrast, etc and a function for flipping and mirroring the picture. It is this last feature I am particularly interested in. I would like a way of controlling that automatically without going through the menu system, and it would be nice to have programmatic control over the other functions too.

The IC used to convert composite video to RGB and sync data for the LCD is MST702-LF by MStar. I found a reference schematic (doesn't match my monitor though), but no data sheet for it. Poking around the PCB with a 'scope, I found some TTL level serial data being generated by the IC, so I hooked it up to my PC to see what was there.

Baud rate was 9600, N-8-1:
Code: Select all
Mstar Semiconductor
[Date]:Dec 26 2011
ACC version: 20051209
DSP version: M2 20070504
FSC version: M2 20060313
AGC version: M9 100 20110902
Maria Ver: 26
Load OK!
[Reset VD]
SetFreeRun delayBack Car ON
[Reset VD]
Save Video Setting!
 WriteTbl <D000>
save setting
VD sync setup mode !
color return
No Line Lock
color return                                                             

My question is, does anyone know anything about this chip and the firmware it's apparently running (Maria v26)? Are there commands I can send it serially to control its mode?

I have tried sending random characters. It seems to respond to certain low-value ASCII codes with one or two '255's, but a '$' character causes a bit more activity. Unfortunately none of it is legible text so I am totally in the dark as to what it means.

Can anyone shed any light?
Last edited by nes on July 24th, 2012, 4:54 am, edited 1 time in total.
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Re: Color TV panel with MStar Controller

Postby nes » July 24th, 2012, 4:53 am

As there is a bonus touch screen it would be rude not to try it out. I requested some samples of AR1100 USB and serial resistive touch screen controller from Microchip a few days ago. A cursory search on Google indicated it was straightforward to get working and well supported by Linux (which is what I am using in this project). Speedy service as ever, they were in my hands yesterday evening. As they're SMD, I etched up a quick breakout board for it:

... and soldered one on together with the required passives scavenged from my small pile of dead hard drives.

Plugged it in to my PC and checked dmesg was happy (which it was second attempt after I switched D- and D+). Yay!
Code: Select all
$ dmesg | tail
[ 3288.757655] usb 2-1.6: new full-speed USB device number 9 using ehci_hcd
[ 3288.854992] input: Microchip Technology Inc. AR1100 HID-MOUSE as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6/2-1.6:1.0/input/input13
[ 3288.855155] generic-usb 0003:04D8:0C02.0004: input,hidraw2: USB HID v1.11 Mouse [Microchip Technology Inc. AR1100 HID-MOUSE] on usb-0000:00:1d.0-1.6/input0

Now I had a problem as the LCD connector looks to be about 0.4mm pitch: a bit too fine for me to solder wires onto. (I did give it a quick go.)

Easily solved though: the touch screen is actually separate from the LCD flexi and the connections are soldered a bit further back. I simply peeled off the bit of kapton tape covering the joints and soldered my wires on there instead. Easy!

Plugged it in and amazingly, not only was it roughly calibrated right but by luck I had managed to get X and Y round the right way and both working in the right directions.

Still want to solve the issues with controlling the LCD panel though.
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Re: TV with MStar IC **Now with added touch screen goodness*

Postby hypers » October 31st, 2012, 3:07 am

Hi, nes,

I have a similar LCD based on the same IC. It is faulty (doesn't start just buzzes from the time being plugged to +12V). I'm trying to repait it.
So far I've found schematics but I suspect it is the same as you have. I share it in case somebody needs it.
Please, have a look at it and tell if you have somewhat different from mine. If so could you please post yours as well?
I also have a datasheet from MStar though for different ICs: MST720... and some others. I don't know if it is of some use but I hope the registers and protocols used are the same or similar.
Since pin-out is clear from the circuit one could work out the way to communicate with MST702 based on data from other part's datasheet. Tell me if you need it.

And do you have any idea why it buzzes or what that supposed to tell me?



P.S.: updated the post in order to resurrect the attachment
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Re: TV with MStar IC **Now with added touch screen goodness*

Postby avjarun » February 5th, 2015, 10:31 pm

Hi all

Sorry to dig this topic again. I was intrested in developing something on my own and as a result I do have purchased MST702-LF IC's. I am planning to test them as specified in the attached MST702 schematics in this thread. Honestly, I dont have any idea on how to select the input source.... flash memory requirement etc.... I dont have a datasheet either. I search all over the internet, but cameup with nothing. I can find datasheets for MST703 but that's entirely off the track and is different. Can anyone please share the datasheet of MST702 please and further advise me for my testing.

Thanks a lot.
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