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Build a digital scale display with smart TFT LCD


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.

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. 


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.