How to use graphic LCD module
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How to use graphic LCD module

Posted Date: 2024-02-03

Many QVGA level LCD modules have built-in display memory. If display data is written using the parallel or SPI interface, the LCD module will continue to drive and display the LCD panel independently. Therefore, even cheap microcomputers can be easily controlled, and such modules with built-in display memory are often used in hobby applications.

However, when sizes exceed QVGA, most LCD modules do not have built-in video memory. Of course, the 3000 yen LCD does not have built-in video memory like the 300 yen LCD. Therefore, in order to use this type of LCD module, an external display memory and LCDC are required to refresh (drive the LCD panel) at a specified time. In the past, separate display circuits were built on separate chips, as shown in the image to the right. Pictured below is a board I made to evaluate a system, it has a 3-chip configuration using a generic LCDC (S1D13506). However, if you plan to design from now on, system configuration using a microcomputer with a built-in LCDC will become more readily available without the hassle of using a general-purpose LCDC or FPGA. Currently, LCDC built-in microcomputers commonly used in hobby applications include LPC2478, LPC1788, SH7262, etc. Especially the latter SH has integrated video memory and can be completed on a single chip.

LCD substrate

Akizuki 3000 yen LCD and Sharp PSP LCD

Pinout comparison

Pin #Akiyuki 3000 Yen Sharp Handheld

1 lead-ground wire

2 LEDs + ground wire

3 ground supply voltages (2.5V)

Four VDD (3.3V) supply voltage (2.5V)

Five→R0

6 → R1

7→R2

8 → R3

9→R4

Ten→R5

11→R6

12→R7

13→G0

14→G1

15→G2

16→G3

17→G4

18→G5

19→G6

20→G7

21→B0

22→B1

23→B2

Twenty-four→B3

Twenty-five→B4

26→B5

27→B6

28→B7

29→Ground wire

30→CK

31→Display

32 CNC synchronization

33 CNC vertical synchronization

34 German CNC

35 CNC AVDD (5V)

36 ground AVDD (5V)

37→CNC

38 CNC Test 1 (NC)

39 CNC test 2 (ground)

40 CNC test 3 (ground)

Appearance comparison (top) Akizuki LCD on the right (bottom) Akizuki LCD is a bit thin

LCD comparison

By the way, this Akizuki 3000 yen LCD has specifications that I have seen somewhere. Yes, it looks a lot like Sharp's PSP LCD (LQ043T3DX02). That LCD module is called PSP LCD because it has been suspiciously circulated as a PSP repair part for a long time. Maybe Akizuki's 3000 yen LCD is the same as the PSP LCD. The reason I decided to try the Akizuki 3000 yen LCD this time is because I thought the PSP LCD substrate I had already made would be easy to use.

When actually viewed, the number of points, overall dimensions, screen size, position, spacing, and number of signal line pins are all the same. The table on the right shows the pin assignments of Akizuki LCD and PSP LCD. I was hoping to get socket compatibility but unfortunately it doesn't. However, the layout of the signal lines is exactly the same, seemingly based on the Sharp PSP LCD design. Probably because it was supplied to the PSP in large quantities, its usage increased and became semi-standard.

You can see that the arrangement and voltage of the power cords make a big difference. The PSP LCD has two power supplies of 2.5V (2.3 to 3.3V)/5V, while the Akizuki LCD has a 3.3V (3.1 to 3.5V) power supply. The backlight (LED) terminal is a separate connector on the PSP LCD, but on the Akizuki LCD it is placed in the same connector as the signal wire. The backlight current is the same.

In addition, Akizuki LCD only uses DE as synchronization signal and does not use HSYNC and VSYNC. Besides horizontal sync, I was wondering what vertical sync was for, but it seems that when there is no DE signal for a certain period of time, this is considered vertical sync. Indeed, this can be connected whether it is time for the front porch or the back porch, and it can be said that this is a clever specification that is very useful. The 3.3V single power supply is also a convenience to use.

The difference in supply voltage is not a problem since I am using a 3.3V/5V PSP LCD. Of course, some of the wiring to the FPC connector needs to be reconnected. If I raised the board I would give up, but since it's UEW wiring the change isn't a big deal. Even so, redoing all the wiring for the LCDC (0.4 mm spacing) was a daunting task.

Terminal switching

←Just switch four jumpers to correspond to Akizuki LCD and familiar PSP LCD.

Viewing angle

The disadvantage of small LCDs is their narrow viewing angle.

This time, based on the existing LCDC board, it can be tried out in 10 minutes, but without any preparation, the LCD module without built-in video memory is still a bit troublesome. If you just want to display an image, I think it's easy to generate a video signal using a lying around ARM board or FPGA board.

The timing parameters of LCDC are the same as those of PSP LCD and do not need to be changed. After all, it seems to be aiming to replace the PSP LCD system without making mechanical changes. Other things I noticed were: the finish of the polarizer, the glossy side of the PSP LCD, and the lack of glare on the Akizuki LCD. The backlight brightness is higher in Akizuki LCDs and is harsh when applying the 20mA standard value. The color rendering is not inferior to that of PSP LCD. The viewing angles of both tend to be similar, wider on the Y-axis and narrower on the X-axis. Tilt beyond 45 degrees on the X-axis significantly reduces contrast, while tilting over 60 degrees inverts contrast, but that's to be expected with a small LCD like this.


#graphic #LCD #module