Week5

 
In the meanwhile of searching 'ideal LCD', I am starting to looking into the specific technical problems which is indicated in the Week4 blog.  Because most of graphic LCD have the similar electrical structure. It will be helpful before the final LCD module is selected.
 
1. Solving interfacing different devices with different signal voltage level.
 
The whole system of Facebook Robotis is modular design.  As a result, The LCD module will have a single micro controller , as a slave controller, to communicate with the master micro controller through I2C communication protocol.  3 major devices will  communicate with eaching other accordingly under different signal voltage levels and there are two major signal voltage level interfaces. One is the LCD module (2.8-3.5 signal voltage level) with the slave micro  controller. The other is the master micro controller (5V signal voltage level) with the slave micro controller.
 
There are two approachs to slove the problem.
1)  find a micro controller which has 2.8-3.5V  signal voltage level and use level shifter to inteface the I2C signal voltage level.
2)   find a micro controller which has 5V  signal voltage level and use level shifter to inteface the LCD with parallel communication protocol.
 
However, there are more pins for parallel communications. The method 2 will not be used. I have found some type of PIC micro controler  which has 3.3V signal voltage level. For I2C communication, some PIC can use external pull up resistors to interface a 5V signal voltage level.  For an univerisal I2C voltage interface solution we can refer to Philips Semiconductor application note AN97055.

Figure 5-1 Level Shifter

 

Due to the similarity of graphic LCD interface, I also created a general schematic circuit diagram which will be finalized when the LCD module is selected.

 

 
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