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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 Table 7. For connection examples, see Section 1.4.3 and

Section 1.4.4.

Table 7. Load Cell Header Pinout

PIN NO.

PIN NAME

FUNCTION

1

EXC+

Positive excitation; connected to +5VA

2

EXCSNS+

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

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