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Series 1: Update - Assembly and Testing (LQ043T3DX02)

Abstract 

0000296The updates presented here are a collection of material, originally presented on Ben Popoola's blog demonstrating the assembling and finally, the working LQ043T3DX02 driver board. The material has been presented in the same style and original format and brings to a completion the notes used to construct the first version of the LQ043T3DX02 driver board. The material in the first section shows some assembly pictures while the following section shows, quite interestingly, the working backlight LED's! The third section shows a charred backlight circuit (whoops) while finally the result of a  working LQ043T3DX02 driver board is presented. 

1:U1.1 PCB Assembly Pictures

Below are some images of the results of the PCB assembly. A quick test and some smoke later revealed that the couple of mods shown in Figure 1 below were needed. The most significant mistake arose from the backlight connector pins being the wrong way around. It should be Pin 1 = VLED- and Pin 4 = VLED+ apart from that everything seems to be working as expected. The result of the smoke is that I now have a spare screen that I can open to see what is inside!

The really pleasing thing that I have noticed is that the test signals sent to an oscilloscope via the BNC connectors are incredibly clean despite the fact that the BNC connectors are next to the switching circuitry!

As soon as I finish writing the device drivers for the LQ043T3DX02 display I will publish Part 6, PCB Assembly, Test and Verification (N.B This will no longer be the case as the next part will begin with a revision of the design and will lead to version 2 of the LQ043T3DX02 driver board - Ed).

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Figure 1:U1-1: Whoops! A couple of mistakes to point out here. The backlight connector pins have been reversed by mistake. A mod quickly fixed that! The oscillator module in the parts list was completely the wrong one. I replaced it with what is needed but the footprint was then wrong!

 

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Figure 1:U1-2: The front of the PCB ...  

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Figure 1:U1-3: .... and quite interestingly the back of the PCB.  The image shows the extent of the ground plane.

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Figure 1:U1-4The LQ043T3DX02 prototype board connected to the Xilinx Spartan 3A starter kit using the FX2 expansion connector. The 6-pin headers have been left unobstructed for future work as can be seen. Mission Accomplished? Well let us see the screen working first!

 

1:U1.2 Working Backlight LEDs

Below are some pictures of the backlight LEDs being driven by the LQ043T3DX02 Driver Board after the modification (mentioned in the previous update, above) have been applied to the backlight connector pin inputs. The big question now is does the R.G,B section of the screen work, even though part of the circuit is damaged? This is something I will test after testing the driver board VHDL code on a new display first.

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Figure 1:U1-5The backlight LED's are connected to the test points TP1 (35.0V) and TP2(GND). (35.0V when measured under no load condition - B.P). The measured voltage across the LEDs is actually 23.8V which seems to be the maximum potential difference across the LEDs for this particular screen. This configuration does not use the current regulation portion of the backlight circuit. (Room Temperature - 23 Degrees Celsius).

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Figure 1:U1-6The backlight LED's are now connected to the backlight connector and the potentiometer is adjusted to produce the minimum voltage across the LEDs. This is measured as 20.3V. (Room Temperature - 23 Degrees Celsius).

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Figure 1:U1-7The backlight LED's are still connected to the backlight connector and the potentiometer is adjusted to produce the maximum voltage across the LEDs. This is measured as 22.7V. (Room Temperature - 23 Degrees Celsius).

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Figure 1:U1-8The The external casing of the LQ043T3DX02 TFT. Notice the burnt lower left hand corner of the white frame. In an assembled unit this sits above the LEDs.

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Figure 1:U1-9: A close up shot of the driver board "driving" the LED's. As mentioned in the comments section previously it seems that there is some kind of extra circuitry related to the backlight LEDs and DISP_ON signal that has been destroyed by reversing the polarity of the backlight connector. However as can be seen above the backklight LEDs have not been affected.

1:U1.3 Charred Backlight Circuit

The original schematics of the LQ043T3DX02 Driver Board (Rev A) erroneously has the positive and negative backlight voltage rails reversed which caused the display to emit "a little bit of smoke" during the initial testing phase. After opening and examining the display the smoke seemed to originate from the next to one of the LED's as can be seen in Figure 1:U1-10 below.

 

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Figure 1:U1-10: The charred section of the backlight is shown circled. What component or components were there and what they did is unknown to me so far (?) Maybe they were used to synchronise the turning on and off of the backlight circuit and the display via the DISP_ON signal? (N.B The red wire is -ve and the black wire is +ve!).
 
I scraped away the burnt area and a very small charred component - it seemed to be a small 0603 passive component - dropped away. I am not sure what this component is but the reverse polarity destroyed it and the signal tracking in that area of the LEDs, rendering the backlight LEDs unusable.

However wiring the LEDs by hand (red and black wires in Figure 1:U1-11) proves that the LEDs still work, as seen in Figure 1:U1-11 below and my previous post (i.e the section above - Ed). The question that arises here is what was charred and what is the overall effect on the display? I will perform some more tests to try and find out.

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Figure 1:U1-11: After rewiring the backlight LEDs and powering-up the LQ043T3DX02 Driver Board (Rev A), when connected to the Spartan 3A starter kit, to my delight the LEDs came on. This proves that the boost circuitry on the LQ043T3DX02 Driver Board (Rev A) is sufficient to power the LE's.

1:U1.4 LQ043T3DX02 Driver Board: Works!

Here are the preliminary results of testing the LQ043T3DX02 Driver Board with the LQ043T3DX02 display module from SHARP. I have generated the timing synchronisaton signals using VHDL and a clock generator (DLL) to convert the 27MHz signal to the 9 MHz clock signal. The design has been simulated using Modelsim XE III 6.4b and ISE Project Navigator 9.0.03i has been used to generate the bit file. The preliminary results are shown in Figures 1:U1-12 -14 below.
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Figure 1:U1-12: R = "11111111", G = "00000000", B = "00000000". Do not be fooled by the washed out looking photography as it does not do the screen justice at all. The colours produced are incredibly vibrant. This is one of the few TFT modules that produces true 24-bit RGB colour.

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Figure 1:U1-13: R = "00000000", G ;= "11111111", B ;= "00000000". Apologies for the quality of the photography yet again.

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Figure 1:U1-14: R = "00000000", G = "00000000", B = "11111111". Apologies for the quality of the photography for the last time!

Why have I highlighted the word SHARP in the first paragraph above, in this section? Well, it seems that there are PSP replacement screens(i.e the LQ043T3DX02 TFT Modules) from different manufacturing sources.

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Figure 1:U1-15The backlight LEDs come on immediately power is supplied to the driver board even when DISP_ON is low.

Does this have any bearing on the results? I do not know, however what is significant about the SHARP module is that the backlight LEDs power up even when there is no configuration in the Spartan 3A FPGA. In this particular example this means that the backlight LEDs are on even when DISP_ON is asserted low, due to the 10K pull down resistor.

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Figure 1:U1-16The only visible difference between the two screens is the embossed word "SHARP" on the screen on the left and the sticker "MADE IN CHINA" on the one on the right. Does this mean that if the reverse polarity is applied to the one on the left the charring would not occur? I do not know and I am not willing to find out just yet!

 

1:U1.5 ... And There She Is!

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Figure 1:U1-17The "Colour Bars on the LQ043T3DX02 Display" image has been generated using the skeleton device driver developed in Series 2 of the Missing Lecture Notes (MLN). Series 2 will focus on developing a graphics library, in a FPGA,  that can be used with microcontrollers.

Demos and applications series 2 to follow including interfacing to a microcontroller. At the moment I feel like I can walk on water I hope that I do not sink too soon! 


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