Hardware
6.2
Power Supply
The ADS1232REF operates from +5VDC and +3.3VDC. These supplies are generated by linear
regulators U1 and U2. Input power comes from either wall-adapter connector J2, or battery connector
BT1. J2 is switched; when a connector is plugged in, BT1 is disconnected.
Noise is important because the ADS1232 voltage reference is typically taken from the power supply. The
supplies are heavily bypassed to reduce noise.
6.3
User Interface
The ADS1232REF user interface consists of the display and switches SW2
–
5 and SW8. Switches are
connected to interrupt-capable GPIOs on the microcontroller, allowing them to wake the microcontroller
from sleep mode.
6.4
ADC Section
The ADC section consists of the ADS1232 device itself and ancillary circuitry.
All signals on the ADS1232 (except for the Channel 2 inputs) are filtered by pass-through capacitors that
help to reject electromagnetic interference (EMI), radio frequency interference (RFI), and noise generated
by the digital circuitry.
6.4.1
Input Circuitry
The ADS1232REF is designed to connect to resistive bridge sensors, particularly load cells. The ADS1232
has two channels. Channel 2 is a direct connection, and does not have filtering. Channel 1 is filtered by
pass-through capacitors C46 and C47 and differential capacitor C7. Common-mode capacitors C32 and
C29 provide additional RF rejection.
6.4.2
Load Cell Header
The load cell header, J6, provides a convenient terminal for load cells having a properly fitted header
connector. It provides excitation and sense connections. The negative excitation line is connected to
ground through analog switch U7, which is controlled by the microcontroller. This arrangement allows for
sleep-and-convert control, which can reduce self-heating in the load cell and conserve power.
The load cell connector
’
s pinout is given in
. For connection examples, see
and
Table 7. Load Cell Header Pinout
PIN NO.
PIN NAME
FUNCTION
1
EXC+
Positive excitation; connected to +5VA
2
Positive sense; connected to external positive reference input
3
SIG+
Input for positive load cell output
4
SIG
–
Input for negative load cell output
5
EXCSNS
–
Negative sense; connected to external negative reference input
6
EXC
–
Negative excitation; connected to ground through switch U7
6.4.3
Input Terminal Block
The input terminal block consists of J4 and J5. It provides connections to all of the analog inputs on the
ADS1232, and connections to the ADS1232REF voltage reference network. Unlike the load cell header,
there are no dedicated excitation outputs. Instead, connections to ground and the 5V supply are provided,
and neither are switched. Also, unlike the header, channel 2 inputs are available on the terminal block.
21
SBAU120B
–
November 2005
–
Revised July 2011
ADS1232REF User
'
s Guide
Copyright
©
2005
–
2011, Texas Instruments Incorporated