5 years, 7 months ago.

ARch Pro with Grove LCD RGB Backlight


I'm trying to use the Grove LCD RGB Backlight v2 with teh ARch pro board but It doesn't work. !!!

I try a lot of different things :

First I try the explanations from this link : http://www.seeedstudio.com/wiki/Example_one_:_Grove_-_LCD_RGB_Backlight

But It doesn't work, the Screen became Red but nothing is printed on the screen.

Did someone have a solution ?

Thanks for your help ! Yann

Question relating to:

Arch Pro, an mbed enabled development board for rapid prototyping.

This LCD module work fine at Ardunio MEGA but I still can not make it work at mbed platform. It may need add R9, R10 2.2K ohm at LCD module?

posted by James Wu 22 Jan 2016

1 Answer

5 years, 7 months ago.

Hi Yann,

It may be an issue of logic level. The input IO logic level of the Grove - LCD RGB Backlight is 5V while the Arch Pro's is 3.3V. As I2C SCL/SDA are open-drain, It may work with 5V pull-up on SCL/SDA.

Regards, Yihui

Accepted Answer

The logic levels are open collector so the Arch Pro is fine. The problem is that the grove connector VCC on the Arch Pro is only 3.3v and the LCD needs 5v. I got it to work by using a Grove Base shield with the switch set to 5v. Also, the LCD RGB modules don't have the pullup resistors installed and I couldn't get it to work without pullups. There are smd pads on the back labeled R9 & R10 and I soldered in 2.2k resistors and it works.

I used the TextLCD Enhanced library with this definition:

I2C i2c_lcd(I2C_SDA,I2C_SCL);

TextLCD_I2C_N lcd(&i2c_lcd, AIP31068_SA, TextLCD::LCD16x2, NC, TextLCD::AIP31068);

posted by B Rey 04 Mar 2015

Yes exactly, with the 5V Pull-up It works fine but why did the LCD give me an acknowledge to my Write Frames ? It's mysterious. On my Grove Base Shield v2, I didn't see smd pad R9 & R10, I only see P1 & P2 near A4 and A5, and they seems to be used to solder a connection between A4 and D14 and A5 and D15 ?

Thanks for your help !

posted by Yann DOUZE 04 Mar 2015

Sorry, R9 & R10 are on the LCD module. Yes, it isn't clear why the RGB LED component works without the pullups but the LCD doesn't.

posted by B Rey 04 Mar 2015