Background

The system we are going to build includes a data acquisition circuit with a host MCU and a HMT050ATA-2C smart LCD module as scale's display.

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HMT050ATA-2C is a smart LCD module with following specifications:

• 5 inch TFT Color LCD with 800 (RGB) x 480 pixels with 16 bits color per pixel and LED backlight
• High-resolution resistive touch panel for user inputs and interactions
• 32 bits ARM Micro-Controller with a Smart LCD Engine to process graphics, commands from host
• A large flash memory to hold graphical data and configuration information locally
• A RS232 or a Logic-Level Serial Interface, connect the module to any host MCU or any other device supporting serial communication
• A USB interface to configure the module

The HMT050ATA-2C provides a very easy and fast way to create high-end embedded applications for Industrial Controls, Instruments, and Medical devices. The TFT LCD module shows user interface, which can be created with Topway's UI development tool. A host MCU may connect to the module, control it and receive input events. 

Content

System Overview

A Digital scale is a very good example explaining the functionality and the way of developing applications with HMT050ATA-2C.

The proposed Digital Scale shall include:

• Two Load Cells
• ADC Board (e.g. based on AD7190) with SPI
• Host MCU Board (e.g. based on a small ARM Cortex M0, PIC or AVR) with SPI and UART
• Smart LCD Module HMT050CC-C with UART
• Power Supply

ADC Board is providing following functionality:

• Converting the bridge voltages of two load cell channels
• A ratio-metric measurement circuit is recommended

The Host MCU is providing following functionality:

• Setup and sampling of ADC values from the ADC Board
• Calculating the actual weights from the ADC values
• Transmitting the weight values as 32 Bit signed Values to the Smart LCD
• Checking some variables inside the Smart LCD and adjusting Modes of operation accordingly
• Recording Tare values in Tare Mode

The HMT050ATA-2C is providing following functionality

• Displaying different pages of contents depends on the operation mode of Host MCU
• Displaying weight values calculated inside the Host MCU
• Setting internal variables depends on Touch Panel events

The Host MCU also connects to the Smart LCD via a asynchronous serial interface in the following format:

• 8 Bit
• No Parity
• 1 Stop Bit.

Additionally, a flow control may be used by setting jumpers JP3 and JP4. Please refer to HMT050ATA-2C user manual for more details.
The Host MCU may use a baud rate of 9600 Bd or 115200 Bd. The baud rate can be selected on the
HMT050CC-C by using Jumpers JP1 and JP2:

• JP1 shorted / JP2 open select 115200 Bd
• JP2 shorted / JP1 open select 9600 Bd

The HMT050ATA-2C smart LCD module

Smart LCD module has the following parts and functions:

• Contents and functionalities are organized in one (or more) page(s)
• Page is a visual display on screen, contains:
  • Images
  • Icons
  • Variables (VP)
  • Animations
  • Time and Date using internal Real Time Clock
• Page can hold multiple touch sensitive areas, which may trigger events like:
  • Transition to another page
  • Showing specific icons
  • Setting variable value or performing calculation
  • Sending touch event via serial interface
  • Sounding internal buzzer
• Page may initialize variable (VP)
• User interaction or serial interface command can control smart lcd module transition from showing one page to another one
• The module includes a memory space, able to store global variables(VP), such as:
  • Numeric value
  • String
  • Graph
  • Bitmaps
• Through serial interface user can do:
  • Switching between pages
  • Text output
  • Graphic operations like drawing line, rectangle and fill
  • Reading and writing of variable
  • Reading current page id
  • Reading and updating internal real time clock
  • Receiving touch event
  • Setting backlight and buzzer
• Save values to internal flash storage

Development Plan

• Define scale's possible operation modes and functions
• Design a Data Acquisition Board with ADC and SPI interface (e.g. refer to AD7190 datasheet)
• Create a simple Host Interface Board with SPI connecting to the data acquisition board, and a serial
  interface that can be used to communicate with HMT050ATA-2C
• Create a design project with multiple pages using Topway UI Editor - RG Tools, which can create Graphical User Interface
  and set internal variables (VP) to respond to user's interactions
• Create communication software for the Host Board, which can sample ADC data, calculate weight and access the internal variables (VP) of HMT050ATA-2C

Continue reading this application note for the whole project.