Geoforce 4-20mA XDCR to Globalstar Interface

The purpose of this project is to interface an industry standard 4-20mA transducer to a remote server by sending simplex transmissions via the Globalstar satellite phone network. In order to fulfill the requirements set by Geoforce’s clients, this device has extremely small power requirements. It is designed to last for 5 years in the field without needing maintenance or recharging.

The above goal was achieved using a microcontroller to digitize the transducer signal and communicate it via an I2C interface.  The I2C interface was connected to a MYTE transmitter which handles the PHY interface to the antenna as well as well as some of the logic required to interface with the Globalstar network.  Additionally, the microcontroller firmware implements some power management techniques as well as runs a calibration procedure on power up to improve accuracy of the digitized signal.

Features & Design Techniques

Power management

  • High efficiency DC-DC conversion
  • Switchable power rails for powering transducer
  • Microcontroller power management enables sleep modes

Error detection and calibration

  • Calibration is performed on startup before the transducer is powered to read the zero signal voltage to remove any offset voltages
  • Microcontroller detects errors such as current outside the 4-20mA range and no transducer connected
  • Errors are further eliminated by averaging multiple readings

Responsibilities & Scope

  • Design of interface circuit to transducer (choke and diode protection)
  • Selection of MCU and design of supporting and debug circuitry
  • Design and implementation of firmware
  • Prototyping, assembly, and testing
  • Project documentation

Additional Project Details

Project Photos




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