Harshana Umesh

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9 years, 10 months ago.  This question has been closed. Reason: Off Topic

i want to help to send usb key board character to ra 8875 display through lpc 1768

2 Answers

David Smart
9 years, 10 months ago.

Hello Harshana,

If I may suggest, you can remove the program from your comment, and replace it with a link to the sample. This will make it easier to read the thread.

Now, for your problem, we will start with some questions -

  1. Is your panel from the same source as the one described in Components | RA8875 Display?
  2. Is it configured for the SPI interface, or one of the others? (this refers to the zero-ohm R1, R2, and R3)?
    • With those resistors in place, trying to communicate is basically a short-circuit from your mbed to power and would drag down the power supply (even damage the mbed if left that way too long).
  3. As there are only 4 signaling wires (SDI, SDO, SCLK and Chip Select), plus power, can you double-check the wiring?
    • Reversing the SPI DI and DO is not uncommon mistake.
  4. When you apply power, do you see anything? (backlight, random stuff)
  5. What prints out on the USB serial port?
  6. Can you add a few lines to blink the mbed LEDs to make sure the mbed is still alive? (this will help determine if you have a power supply problem).

change this:

while (1)
        ;

to this:

while (1) {
    myled = 1;
    wait(0.2);
    myled = 0;
    wait(0.2);
}

of course, you'll need the "DigitalOut myled(LED1);" up at the top.

Accepted Answer

Oh, and are you using the same SPI port as shown in the schematic on the display page? (and is anything else attached to that same port?)

posted by David Smart 11 Jun 2014

Dear David,

Thanks for your consideration and Reply.

For your questions,

1)Yes. I ordered the exact same one. 2)Yes, I removed all three resistors R1,R2 &R3. 3)Yep, Wirings are correct. It was my first checking when system didn't work. 4)Nothing. Not even a light. 5)I did not check the USB. I used a regulated 5v power supply. And power receiving is checked and ok with MBED and Display. 6)I checked the MBED. It is working fine with my other projects, and as well as LED Blink program.

So, what would be the problem i'm having? Pls help.

Thanks again.

posted by Harshana Umesh 11 Jun 2014

Where is your regulated 5v supply connected? In the diagram on the display page, it is using the 5v out from the mbed to the display. This isn't the only possibility, but if you are providing 5v to the mbed and there is any voltage drop, perhaps it ends up too low by the time it is feeding the display chips. Please make sure you have 5v to the display, and maybe double-check that the display module is configured for 5v, and not 3.3v (more zero-ohm resistors on the module).

mbed pins 5, 7, and 12 are signals to the display module, so, let's simplify the program to something like this (removing the RA8875 driver from the picture, just testing the individual pins).

BusOut a(p5, p7, p12);
BusOut a1(LED1, LED2, LED3);

void main() {
    unsigned char i = 0;
    for (;;) {
        a1 = a = (i & 7);
        wait(10);
        i++;
    }
}

I didn't actually compile this, but hope there are no errors. Basically, use something like this to slow the signals down so you can check the voltage on each pin and ensure they are connected properly, end to end.

If this doesn't help, do you have another display? I don't know how sensitive this display module is to static electricity, which could permanently damage it. Others are using the display library without this problem, so I'm beginning to struggle a bit on fresh ideas to help you out.

If you have another display, based on the RA8875 and configured for SPI, it should work. I only created the driver for a 280x272, some RA8875 displays have a different resolution. You can modify the source if it isn't quite matched up. Best of luck to you.

19 Jul 2014 Follow up: Harshana tried a different display, and has reported that the demo programs are working properly.

posted by David Smart 13 Jun 2014

Dear David,

Thanks for the reply.

I'll follow your advice and reply you soon. I have another display module of 5". Will it compatible with this program?

Thanks.

posted by Harshana Umesh 16 Jun 2014
Gary Richardson
9 years, 10 months ago.

Have you tried both SPI ports? I had better luck using SPI1 (pins 11, 12, 13)

Dear Gary,

Thanks for the opinion.

posted by Harshana Umesh 26 Jun 2014

new display is working properly

posted by Harshana Umesh 20 Jul 2014