Datasheet

Evaluation Board User Guide UG-280
Rev. 0 | Page 5 of 20
USING THE AD7191 EVALUATION BOARD IN STANDALONE MODE
The AD7191 evaluation board can be operated in standalone
mode. In this mode, the evaluation board functions as a weigh
scale demonstration. Channel AIN3/AIN4 is the analog input
channel. The AIN3 and AIN4 pins, along with REFIN(+),
REFIN(−), AV
DD
, and AGND, are connected to the J4 header.
This header allows the user to connect a load cell to the AD7191.
The load cell should be connected to the header as shown in
Figure 6. A 6-wire load cell is shown, but a 4-wire load cell can
also be connected.
EXC+
EXC–
OUT–
OUT+
SENSE+
SENSE–
GND/SHLD
AVDD/EXC
REF1(+)
AIN3(+)
AIN4(–)
REF1–
PWR_SW
GND/SHLD
J4
09880-006
Figure 6. Load Cell Connection to Header J4
The AD7191 is configured for an update rate of 10 Hz. The gain
is programmed to 128. Channel AIN3/AIN4 is selected as the
active channel. Figure 7 shows the positions of the switches on S6.
S6
ODR2
ODR1
CLKSEL
PGA1
CHAN
TEMP
PGA2
ONOFF
09880-007
Figure 7. Switch S6 Positions for Load Cell Connection
The conversions from the AD7191 are displayed on the LCD
display. The four buttons beneath the LCD display allow the
user to calibrate the weigh scale system, adjust the LCD con-
trast, and read the offset and gain registers. The function of
each button is listed at the bottom of the LCD display.
To operate the weigh scale demonstration, connect the load cell
to Header J4, as shown in Figure 6. Apply power to the AD7191
evaluation board using either a 9 V battery or a 9 V DC power
source. Ensure that Link J1 is in the 5 V BAT/EXT position. The
weigh scale demonstration can also be powered from the USB
connector if the board is connected to a PC. Link J1 should be
in the 5 V USB position in this case.
With no weight on the weigh scale, an offset calibration should
be performed (selectable from the buttons below the LCD
display). The expected full-scale weight should then be placed
on the load cell and the full-scale calibration performed. The
user should select the corresponding full-scale weight on the
LCD display because the weigh scale demonstration supports
full-scale weights of 500 g to 10 kg. The software then continu-
ously reads conversions from the AD7191, scales the conversions
appropriately, and displays the resulting weight on the LCD
display.