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LCD I2C Backpack I2C device not recognized
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LCD I2C Backpack I2C device not recognized

by mnishiguchi on Sun Jan 03, 2021 11:15 pm

Hi!
Adafruit support, Jessie Mae referred me here.

1) Tell us what product you are asking about, your Adafruit order number, and when you purchased the item.

Products I purchased and have some issue with:

- RGB backlight positive LCD 20x4 + extras (black on RGB) [ID:499]
- i2c / SPI character LCD backpack[ID:292]

Issue:

- The I2C backpack is not recognized as I2C device.
- Also looks like the LCD is not even powered on, despite being connected to the Pi.

I have done the same thing with other manufacture's I2C backpack and it works with no problem.
I believe that I assembled and wired them correctly.
I double-checked the wiring and it is correct. The LCD is the only device I connect to my Raspberry Pi Zero.


2) Post clear photos, focused, and detailed pictures of the front and back of the boards, as well as any connections to the board.

- photos attached
- wiring from I2C backpack to Raspberry Pi Zero:

    - GND -> #6 GND (brown jumper)
    - 5V -> #4 5V (red jumper)
    - CLK -> #5 I2C SCL (yellow jumper)
    - DAT -> #3 I2C SDA (green jumper)

3) For software issues, please post the complete text of your IDE's error message. Please use the [code] tag when posting error message as well as code.

N/A

Attachments


Am I missing something? Or possibly defective?

Thank you for your assistance!

mnishiguchi
 
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Joined: Sun Jan 03, 2021 11:27 am

Re: LCD I2C Backpack I2C device not recognized

by adafruit_support_mike on Mon Jan 04, 2021 4:36 am

Try adjusting the contrast potentiometer on the LDD Backpack (near the terminal labeled DAT).

LCDs require a bias voltage to work properly, and that can vary from one display to the next. Taking the bias voltage toward zero makes the display darker, taking it toward 5V makes it lighter. If the bias is too high, it can look like the display isn't doing anything. If the bias is too low, all the characters just look like black rectangles.

Also check the 5V supply at the screws in the terminal blocks for the Backpack. There's always a chance you might have a jumper whose wire is broken inside the insulation.

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Re: LCD I2C Backpack I2C device not recognized

by mnishiguchi on Wed Jan 06, 2021 8:11 pm

adafruit_support_mike wrote:Try adjusting the contrast potentiometer on the LDD Backpack (near the terminal labeled DAT).

LCDs require a bias voltage to work properly, and that can vary from one display to the next. Taking the bias voltage toward zero makes the display darker, taking it toward 5V makes it lighter. If the bias is too high, it can look like the display isn't doing anything. If the bias is too low, all the characters just look like black rectangles.

Also check the 5V supply at the screws in the terminal blocks for the Backpack. There's always a chance you might have a jumper whose wire is broken inside the insulation.


Thanks Mike,

I've moved forward a bit. I moved the potentiometer and saw the contrast change.
Does the display in the photo below look normal to you? (I only see 1st and 3rd rows highlighted)
I am asking you because this is my first time using 20x4 LCD. I have used 16x2 before.

![20210106_190029(0)](https://user-images.githubusercontent.c ... 369357.jpg)

mnishiguchi
 
Posts: 19
Joined: Sun Jan 03, 2021 11:27 am

Re: LCD I2C Backpack I2C device not recognized

by adafruit_support_mike on Thu Jan 07, 2021 6:55 pm

That looks like a display where the contrast is set a little too high. Adjust the contrast down a bit until the dark blocks go away, then try sending some text to the display.

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Re: LCD I2C Backpack I2C device not recognized

by mnishiguchi on Sat Jan 09, 2021 11:37 pm

adafruit_support_mike wrote:That looks like a display where the contrast is set a little too high. Adjust the contrast down a bit until the dark blocks go away, then try sending some text to the display.


I am trying to print text but the display won't show anything, not even garbage chars :(

What I am doing is exactly the same as what I did before with other cheap I2C backpack. I re-confirmed that code and other backpack is still working perfectly.

Here is my "past" demo: https://dev.to/mnishiguchi/elixir-nerve ... rface-31ca

I assume the same program should work. Is this assumption wrong? I2C communication can be different with Adafruit I2C backpack?
Am I missing something?

Thanks!

mnishiguchi
 
Posts: 19
Joined: Sun Jan 03, 2021 11:27 am

Re: LCD I2C Backpack I2C device not recognized

by mnishiguchi on Sun Jan 10, 2021 2:30 pm

Ah I have a feeling that my code for other manufacture's i2c backpacks does not work for Adafruit's.
If that is the case in a general sense, probably the products are good then.

I scanned through data sheets.

    Cheap i2c backpacks use PCF8575 - (I own and used it before)
    Adafruit's i2c backpacks use 74LS595 - (a product I purchased)
    Adafruit's LCD Pi Plate uses MCP23017 - (another product I purchased)

I may need to revise my custom driver code for MCP23017 and 74LS595.

FYI: I am trying to write my own drive code using Elixir programming language.
https://github.com/mnishiguchi/lcd_display

mnishiguchi
 
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Re: LCD I2C Backpack I2C device not recognized

by mnishiguchi on Mon Jan 11, 2021 10:22 pm

OK i figured it out. Writing code following MCP23008 data sheet, the display worked.
Thanks a lot.

mnishiguchi
 
Posts: 19
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Re: LCD I2C Backpack I2C device not recognized

by adafruit_support_mike on Sat Jan 16, 2021 2:10 am

Glad to hear you got things working!

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Please be positive and constructive with your questions and comments.