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RGB LCD Shield kit with 3.3V controller
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RGB LCD Shield kit with 3.3V controller

by EirikS on Wed Nov 11, 2020 10:40 am

Hi,

First of all, I'm quite new to electronic projects, so still have a lot to learn. So please excuse any signs of ignorance :)

I've purchased the RGB LCD Shield Kit w/ 16x2 Character Display I2C (product ID 714) to use to control an IoT platform I'm building. The LCD shield will not be used as a shield, but mounted in a separate box.

Question is; The microcontroller I'm using is the Arduino NANO 33 IoT. This board is 3.3V.

Can I run the LCD display off 3.3V? I'm powering the platform with 12V input and a 3.3V buck converter so I don't have the limitation of current from the Arduino.

Alternatively, I'm also considering supplying 5V using a second buck converter to power the LCD shield and possible some other components. If so, is it possible to connect the SDA and SCL lines directly to the Arduino's IOs? I presume the I2C lines of the LCD shield are 5V too if supplied 5V VIN, while the upper voltage for the IO ports are 3.8V, and as such, will not work(?).

If my assumptions are correct so far, I could consider using a 10 kohm resistor inline with the SDA and SCL lines, but doubt this will work since the LCD display will be mounted at some distance from the controller. Is an alternative to use a level-shifter chip?

Or am I barking up the wrong tree?

Any enlightenments are welcome!


Best regards,

Eirik

EirikS
 
Posts: 3
Joined: Wed Nov 11, 2020 9:48 am

Re: RGB LCD Shield kit with 3.3V controller

by adafruit_support_bill on Wed Nov 11, 2020 11:09 am

This display uses the 5v pin to power the backlight as well as the pullup voltage for the i2c bus.
You could power the board with 5v and use a level shifter.
You could try powering it with 3.3v via the 5v pin on the shield. But they backlight would likely be a bit dim - especially the blue channel.
Or you could power with 5v and do a bit of board surgery to change the pullups to 3.3v.

The Pi version would be simpler since it is designed for 3.3v operation: https://www.adafruit.com/product/1109
If your board is unused and you would like to exchange it, please contact support@adafruit.com with a link to this thread.

adafruit_support_bill
 
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Joined: Sat Feb 07, 2009 10:11 am

Re: RGB LCD Shield kit with 3.3V controller

by EirikS on Wed Nov 11, 2020 12:36 pm

First of all, thank you for the quick answer!

I wish I knew of the Pi version, but returning the one I have is not practical since I live in Norway.

So I guess the easiest approach is to use a level shifter. For my application, I presume the BSS138 (PRODUCT ID: 757) would be the best choice? I was trying to find the pinout specs for this, bus it seems to elude me. But from the annotations, it seems to be as follows:
LV: 3.3V in
HV: 5V in
A1-4: IO from Arduino, 3.3V
B1-4: IO from component, 5V

I will only use A/B 1-2 for the I2C.

In KiCAD, I've added two 6-pin male connectors to plug the BSS138 board directly into my PCB. I've connected A1 to SDA (A4 on the Arduino NANO) and A2 to SCL (A5). I will connect the SDA and SCL lines from the LCD to B1 and B2. Presume this is correct? Presume also I will not need to add any other components for this to work properly?

Is it ok to connect other 5V I2C components to B1/B2 in parallel?


Best regards,

Eirik

Best regards,

Eirik

EirikS
 
Posts: 3
Joined: Wed Nov 11, 2020 9:48 am

Re: RGB LCD Shield kit with 3.3V controller

by adafruit_support_bill on Wed Nov 11, 2020 1:15 pm

Yes. The BSS138 is the right type of level shifter and your proposed connections all look correct. You can connect multiple i2c devices to either the HV or LV side of the shifter as needed.

adafruit_support_bill
 
Posts: 79456
Joined: Sat Feb 07, 2009 10:11 am

Re: RGB LCD Shield kit with 3.3V controller

by EirikS on Wed Nov 11, 2020 2:43 pm

Great, thanks for your help! :)

EirikS
 
Posts: 3
Joined: Wed Nov 11, 2020 9:48 am

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