Analog Devices: CN0221 Reference Design for USB-Based Temperature Monitor Using the ADuCM360 Precision Analog Microcontroller and an External Thermocouple

atomar — Thu, 04 Apr 2013 10:17:12 GMT

Current Revision posted to Documents by atomar on 4/4/2013 10:17:12 AM

BUY NOWBUY NOW

Kit Overview

This circuit uses the ADuCM360ADuCM360/ADuCM361ADuCM361 precision analog microcontroller in an accurate thermocouple temperature monitoring application. The ADuCM360/ADuCM361 integrates dual 24-bit sigma-delta (Σ-Δ) analog-to-digital converters (ADCs), dual programmable current sources, a 12-bit digital-to-analog converter (DAC), and a 1.2 V internal reference, as well as an ARM Cortex-M3 core, 126 kB flash, 8 kB SRAM, and various digital peripherals such as UART, timers, SPIs, and I2C interfaces.

In the circuit, the ADuCM360/ADuCM361 is connected to a thermocouple and a 100 Ω platinum resistance temperature detector (RTD). The RTD is used for cold junction compensation.

In the source code, an ADC sampling rate of 4 Hz is chosen. When the ADC input programmable gain amplifier (PGA) is configured for a gain of 32, the noise-free code resolution of the ADuCM360ADuCM360/ADuCM361ADuCM361 is greater than 18 bits.

The ADuCM360 is a fully integrated, 3.9 kSPS, 24-bit data acquisition system that incorporates dual high performance, multichannel sigma-delta (Σ-Δ) analog-to-digital converters (ADCs), a 32-bit ARM Cortex-M3 processor, and Flash/EE memory on a single chip. The ADuCM360 is designed for direct interfacing to external precision sensors in both wired and battery-powered applications. The ADuCM361 contains all the features of the ADuCM360 except that only one 24-bit Σ-Δ ADC (ADC1) is available.

Key Applications: Field Instruments/ Smart Transmitters, Sensors and Sensor Interface, Temperature Controllers

More Development Kits and Tools
	More Analog Devices Analog Development Kits		Analog Devices MCU based Development Kits
	Development Platforms & Kits		element14 Knode

Technical Documents

Learning Center

Type	Description
User Manual	ADI: User Manual for CN0221 USB-Based Temperature Monitor Using the ADuCM360 Precision Analog Microcontroller and an External Thermocouple
Datasheet	ADI: Datasheet for ADuCM360/ADuCM361: Low Power, Precision Analog Microcontroller with Dual Sigma-Delta ADCs, ARM Cortex-M3 (Rev A)
Datasheet	ADI: Datasheet for ADP1720: 50 mA, High Voltage, Micropower Linear Regulator (Rev A)
Application Note	ADI: Application Note (AN-1111) for Options for Minimizing Power Consumption When Using the ADuCM360/ADuCM361
Application Note	ADI: Application Note for I2C-Compatible Interface on Cortex-M3 Based Precision Analog Microcontroller (ADuCxxx Family)

Design Elements

Type	Description
Schematics	ADI: Schematics for EVAL-ADuCM360TCZ Evaluation Board
Layout	ADI: Layout for EVAL-ADuCM360TCZ
BOM	ADI: Bill of Material (BOM) for EVAL-ADuCM360TCZ Evaluation Board

Video

Kit Features

The following features of the ADuCM360ADuCM360/ADuCM361ADuCM361 are used in this application:

A 24-bit Σ-Δ ADC with a PGA set for a gain of 32 in the software for the thermocouple and RTD.
- The ADC1 was switched continuously between sampling the thermocouple and the RTD voltages.
Programmable excitation current sources for forcing a controlled current through the RTD.
- The dual current sources are configurable in from 0 μA to 2 mA. For this example, a 200 μA setting was used to minimize the error introduced by the RTD self-heating.
An internal 1.2 V reference for the ADC in the ADuCM360/ADuCM361.
- It measures the thermocouple voltage; the internal voltage reference was used due to its precision.
An external voltage reference for the ADC in the ADuCM360/ADuCM361.
- It measures the RTD resistance; a ratiometric setup was used where an external reference resistor (R_REF) was connected across the external VREF+ and VREF− pins.
A bias voltage generator (VBIAS).
- The VBIAS function was used to set the thermocouple common-mode voltage to AVDD/2.
The ARM Cortex-M3 core. T
- he powerful 32-bit ARM core with integrated 126 kB flash and 8 kB SRAM memory runs the user code that configures and controls the ADC, processes the ADC conversions from the RTD, and controls the communications over the UART/USB interface.
The UART was used as the communication interface to the host PC.
Two external switches are used to force the part into its flash boot mode.
- By holding SD low and toggling the RESET button, the ADuCM360/ADuCM361 enters boot mode instead of normal user mode. In boot mode, the internal flash can be reprogrammed through the UART interface.

Kit Contents

The Analog Devices EVAL-CN0221-EB1ZEVAL-CN0221-EB1Z kit is supplied with below contents:

Evaluation Board

Tags: aducm361, eval-cn0221-eb1z, aducm360, analog_devices