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GS3 Integrator Guide

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SENSOR COMMUNICATION TYPES

Decagon digital sensors feature a 1-wire serial interface for communicating sensor measurements. The

sensor supports two different protocols: SDI-12 and DDI-Serial. Both interfaces are documented in this

guide. Each protocol has advantages and implementation challenges. There are differences in voltage

levels, logic levels, and signal timing for each protocol. Please contact Decagon with your specific

requirements if the protocol choice for your application is not obvious.

SDI-12 INTRODUCTION

SDI-12 is a standards-based protocol for interfacing sensors to data loggers and data acquisition

equipment. Multiple sensors with unique addresses can share a common 3-wire bus (power, ground, and

data). Two-way communication between the sensor and logger are possible by sharing the data line for

transmit and receive as defined by the standard. Sensor measurements are triggered by protocol

command.

DDI-SERIAL INTRODUCTION

The DDI-Serial protocol is the method used by the Decagon's family of data loggers for collecting data from

the sensor. This protocol uses the data line configured to transmit data from the sensor to the receiver

only (simplex). Typically the receive side is a microprocessor UART or a general-purpose IO pin using a "bit-

bang" method to receive data. Sensor measurements are triggered by applying power to the sensor.

INTERFACING THE SENSOR TO A PC

The serial signals and protocols supported by the sensor require some type of interface hardware to be

compatible with the serial port found on most personal computers (or USB-to-Serial adapters). There are

several SDI-12 interface adapters available in the marketplace; however, Decagon has not tested any of

these interfaces and cannot make a recommendation of which adapters work with Decagon sensors.

Decagon's Em50 data logger and ProCheck hand-held both are able to operate as a computer-to-sensor

interface for making on-demand sensor measurements.

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