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This page gives an overview of using the Analog Devices Sigma Delta ADCs with Cortex-M3 ARM processor based ADuCM3029 Cog Eval Board. The intended demo application shows how to convert an external sensor data into actual units and transmit them over either Bluetooth or UART link using ADuCM3029 Cog board and Bluetooth Eval board. The operation can be better illustrated using below diagram.
The below diagram shows the temperature sensing scheme using AD7124 Sigma Delta ADC. It uses T-Type thermocouple and 2-wire RTD sensors as an external analog inputs. The Thermocouple acts as a hot junction and RTD as a cold junction compensation. This combination provides a precise measurements of ambient temperature over a very wide range (-200C to +400C).
AD7124 Eval board has default on-board KTY-81/110 RTD sensor (silicon Thermistor) connected between analog inputs AIN4 and AIN5. However, for the complete RTD measurement, the precision resistor (Rref) needs to be connectd externally along with Rhead headroom resistor. Rref needs to have 0.1% precision for complete accuracy. The choice of this reference resistor depends upon the Ref output voltage and excitation current. Use below application note for more details on the temperature sensing using RTD:
RTD Measurement System Using a Precision Sigma-Delta ADC
Thermocouple needs to be connected externally between analog inputs AIN2 and AIN3. Use below application note for more details on the temperature sensing using Thermocouple:
Thermocouple Measurement System Using a Precision Sigma-Delta ADC
For temperature sensing using AD7124 Eval board and ADuCM3029 COG board please use below hardware configuration:
The ADuCM3029 COG board is connected to Sigma Delta Eval board using a Gear Expander board. Depending upon the digital interface used on Sigma Delta ADCs, the connection could be either 4 line SPI or 3 line I2C. The connection can be done either using SDP breakup board or by directly soldering fly wires from the ADC Evaluation board to ADuCM3029 Expander Gear board. The sample connection for the AD7124 Eval board with COG board is shown below using a fly wires. The wires are directly soldered on the Eval board, but for better connection, use the SDP breakout board: