LK204-7T-1U: I2C and voltage levels.

LK/ELK/VK/PK/OK/MX/GLK/EGLK/GVK/GLT Series

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va3bit
LCD?
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Joined: Tue Apr 20, 2010 6:53 am
Location: Ottawa

LK204-7T-1U: I2C and voltage levels.

Post by va3bit » Tue Apr 20, 2010 7:17 am

Hello Everyone,

My first post. 8) Yes, I'm a newbie, but I did do a search and didn't find anything. :(

I recently purchased an LK204-7T-1U-GW for use with a Picaxe controller. I plan to use I2C to communicate as I need to use the serial port on the Picaxe for RS485 communication. I was reading the manual for the display, and have this question:

In paragraph 4.1.1, page 17, line 3, it states "The I2C lines operate at 5V normally or 3.3V for -1U style units".

Is the line above a typo? It doesn't make sense to me that a display with a supply voltage of 5V would then drop the I2C voltage to 3.3V. Not to mention that it makes the design difficult as the Picaxe uses 5V and I need to interface with other devices on the I2C lines too. Can anyone confirm that the "3.3V for -1U style units" is a typo and should read "3.3V for -LV style units", the "-LV" being Matrix Orbital's low voltage (3.3V) version of the display?

Thanks,
Arthur

Paradigm
Matrix Orbital
Matrix Orbital
Posts: 255
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Location: Calgary, Alberta, Canada

Post by Paradigm » Tue Apr 20, 2010 9:06 am

Welcome to Matrix Orbital Forums va3bit,

Unfortunately that is not a typo. While the supply is 5V, the display itself is 3.3V internally. One suggestion I can make is to check out:

http://ics.nxp.com/support/documents/in ... n97055.pdf

It outlines a way to do bi-directional I2C shifting with two MOSFET transistors. Just about any small MOSFET transistors will do. Too large and they won't be able to switch fast enough, so don't use ones for switching motors or the like.
James McTavish, P.Eng
Director of Engineering
Matrix Orbital

va3bit
LCD?
Posts: 2
Joined: Tue Apr 20, 2010 6:53 am
Location: Ottawa

Post by va3bit » Wed Apr 21, 2010 9:13 am

Hello Paradigm,

Thanks for your quick reply. The statement "The I2C lines operate at 5V normally or 3.3V for -1U style units" implies that Matrix Orbital sells some displays for which the I2C lines do operate at 5V. Can you tell me which ones those displays are? Or, are they all displays without the "-1U" designation?

I asked HVWTech.com (Solarbotics), where I bought your display, the same question and they replied that although the -1U displays operate on 3.3V, the -1U displays are 5V tolerant (and can be used as shown in Fig. 1 of the an97055.pdf document you attached to your post).

:-?

BTW, the display itself looks fabulous!

Thanks,
Arthur

Paradigm
Matrix Orbital
Matrix Orbital
Posts: 255
Joined: Thu Sep 13, 2001 6:00 pm
Location: Calgary, Alberta, Canada

Post by Paradigm » Wed Apr 21, 2010 9:36 am

Hi Arthur,

The only ones that have the 3.3V core are the LK204-7T-1U and the GLK19264-7T-1U. Everything else we have is 5V core.
James McTavish, P.Eng
Director of Engineering
Matrix Orbital

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