This version (29 Jul 2021 08:38) was approved by Harvey John De Chavez.The Previously approved version (29 Jul 2021 07:20) is available.Diff

Complete Closed-Loop Precision Analog Microcontroller Thermocouple Measurement System with 4 mA to 20 mA Output (CN0300)


This circuit using the ADUCM360 shows how a thermocouple and RTD can be amplified and sampled using the internal Programmable Gain Amplifier and high performance ADC. The DAC output is then set to control the 4-20mA transmitter interface. CN0300 demonstrates the high performance and circuit integration of the ADUCM360 - Amplifier, ADC, CPU, DAC and OP-AMP all in one-chip!

General Setup

Minimum PC/System Requirements

  • One PC with the following
    • Windows XP SP2, Windows Vista or Windows 7 Business/Enterprise/Ultimate editions
    • Intel Pentium processor (x86 compatible), 1GHz or faster
    • 512 MB RAM and 1 GB available hard disk space
    • USB port

How to Install the Evaluation Software

  1. Ensure your PC has the USB drivers for the USB-SWD/UART board.
    1. To Install the drivers for the USB-SWD/UART board, unzip the CDM file for Windows XP drivers
    2. For other operating systems, go to the FTDI website:

Step by Step Instruction for Connecting the Hardware

  1. Connect the EVAL-CN0300-EB1Z board to the USB-SWD/UART board.
  2. Connect a 12V power supply to J3. Make sure to connect a Current Meter in series with the 12V terminal. Short the inputs to J2 together
  3. Connect the USB-SWD/UART board to your PC via a USB cable. (Ensure the driver is installed correctly)

Opening and Enabling the Evaluation Software

  1. You now need to determine what com port your PC has allocated to your USB-SWD/UART board
  2. Go to “Settings, Control panel, System, Hardware, Device Manager” – see example below where COM port 56 was allocated.
  3. Press the reset button on the EVAL-CN0300-EB1Z board and the following should appear on the HyperTerminal window: the current reading on the current meter should match the value “Expected DAC Current” on your screen.

Calibrating the DAC (Only needed if a Recalibration is desired)

  1. Next open the application CM3WSD.exe
  2. Using the “Browse” tab, call the file CN0300_test.hex
  3. Select the “Configure” tab and select the ADUCM360 in “Parts” tab.
  4. Select “Comms” tab. Select the appropriate COM port as determined in step 5. A baud rate of 9600 is fine.
  5. Select “Command” tab. Enable the “program and verify” tabs.
  6. Next, force the part into download mode – to do this, hold the “SD” button on the EVAL-CN0300-EB1Z board while pressing and releasing the “RESET” button.
  7. Click the “Start” button on CM3WSD. You will see the following:
  8. Next close CM3WSD and open HyperTerminal on your PC.
  9. Set Hyperterminal for the appropriate COM port and for 9600 baud rate, 8 data bits, No parity, 1 stop bit, no flow control.
  10. Press reset and the following should appear on your PC:
  11. Your current meter should report a value close to 4mA – if it doesn’t follow the instructions on the HyperTerminal screen to calibrate the DAC output to 4mA by pressing the “1” or “0” keys accordingly. Ensure you select the HyperTerminal screen before pressing 1 or 0.
  12. Press return when the current meter reports 4mA
  13. Repeat step 13 for the 20mA calibration.
  14. After this the program will continuously output the following information:
  15. The Final temperature reported should be within a few degrees C of the expected ambient temperature. +/-5C is fine since the ADC is not fully calibrated.
  16. Temporarily disconnect the COM port from HyperTerminal by pressing the phone tab.
  17. Repeat Steps 3 to 9 except this time, select the file CN0300_Final.hex. This file is very similar to the test program except it does not call the DAC calibration function.
  18. Close CM3WSD. Return to HyperTerminal and select “Connect” by pressing the phone icon.


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resources/eval/user-guides/circuits-from-the-lab/cn0300.txt · Last modified: 29 Jul 2021 08:38 by Harvey John De Chavez