The AD7780 is a complete low power front-end solution for bridge sensor products, including weigh scales, strain gages, and pressure sensors. It contains a precision, low power, 24-bit sigma-delta (Σ-Δ) ADC; an on-chip, low noise programmable gain amplifier (PGA); and an on-chip oscillator.
System: Microblaze, AXI, UART
The bit file provided in the project *.zip file combines the FPGA bit file and the SDK elf files. It may be used for a quick check on the system. All you need is the hardware and a PC running a UART terminal and the programmer (IMPACT).
If you are not familiar with LX9 and/or Xilix tools, please visit
http://www.xilinx.com/products/boards-and-kits/AES-S6MB-LX9.htm for details.
If you are not familiar with Nexys™3 and/or Xilix tools, please visit
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,897&Prod=NEXYS3 for details.
Extract the project from the archive file (AD7780_<board_name>.zip) to the location you desire.
To begin, connect the PmodAD3 to J5 connector of LX9 board (see image below). Connect the USB cable from the PC to the USB-UART female connector of the board for the UART terminal. The board will be programmed through its USB male connector.
To begin, connect the PmodAD3 to JA connector of Nexys™3 board (see image below). Connect the USB cables from the PC to the board, one for programming (Digilent USB device) and one for the UART terminal (FT232R USB UART).
Start IMPACT, and double click “Boundary Scan”. Right click and select Initialize Chain. The program should recognize the Spartan 6 device (see screenshot below). Start a UART terminal and then program the device using the bit file provided in the project *.zip archive, located in the “sw” folder (../ad7780/sw/AD7780.bit).
If programming was successful, the Main Menu will appear in your UART terminal, as seen in the pictures below. There are 6 options available for you. Use [v], [f], [g], [p], [r], [s], [m] in order to choose the desired one.
Display Vin allows printing the input voltage over the UART with the appropriate output rate (10 Hz or 16.7 Hz, depending on Filter settings). Pressing [m] will return to menu.
If the device is Powered Down the user will be prompted to Power Up the device prior to trying to display the input voltage.
Change Filter Option allows selecting between 10 Hz and 16.7 Hz Output Rate.
Change Gain Option allows selecting between a gain of 128 or a gain of 1.
Power Down / Power Up allows powering down the device or powering it back up.
Modify Voltage Reference allows changing the voltage reference that is used to calculate the value displayed over UART. The default value is 3300 mV. If using another reference voltage, please modify it here before printing values, in order to obtain correct results. If any value besides 1 to 9 is entered, an error message will be displayed. If a value higher than 5000 is entered, an error message will be displayed. If entering less than 4 characters, please press [Enter] in order to validate your input. If 4 characters are entered, the result is automatically validated.
Input errors are displayed in the following picture.
Display current settings allows printing the current settings for the device. Any pressed key will take you back to the menu.
The reference design is a custom communication interface, allowing control for the FILTER, GAIN, PDRST pins, reading data from the AD7780 and generating an interrupt when data has been received.