We are excited to announce that uRADMonitor CITY now supports SDI-12, the industry-standard serial digital interface widely used in environmental monitoring and data acquisition. With this update, uRADMonitor CITY can be connected directly to dataloggers, PLCs, weather stations, and other SDI-12 compatible equipment, opening the door to deployments in scientific, industrial, and municipal monitoring networks that rely on this protocol. This option will be provided to some of the other uRADMonitor sensors, including the uRADMonitor MODEL A3 and the uRADMonitor MODEL INDUSTRIAL.

What Is SDI-12 and Why Does It Matter?

SDI-12 stands for Serial Digital Interface at 1200 baud. It is a standardized communication protocol developed specifically for environmental sensors and dataloggers. Despite its simplicity with just a common ground and a 5V signal it has become the backbone of field instrumentation across hydrology, meteorology, soil science, and air quality monitoring worldwide.

The protocol works like this: a datalogger sends a wake-up BREAK signal on the bus, followed by a short ASCII command addressed to a specific sensor. The sensor responds with its data, formatted as a string of signed decimal values. Multiple sensors can share the same SDI wire, each identified by a unique single-character address (0–9, A–Z, a–z), giving a single bus the ability to address up to 62 devices simultaneously.

For uRADMonitor, SDI-12 support is significant for several reasons. Many professional environmental monitoring deployments, particularly in government networks, universities, and research institutions, are built around SDI-12 dataloggers such as Campbell Scientific, Onset HOBO, or similar systems. These installations already have the wiring infrastructure, the logging software, and the data pipelines in place. By speaking SDI-12 natively, the uRADMonitor sensors connect directly into these environments without any additional converters, gateways, or custom software.

It is also a step toward interoperability. Air quality data is most valuable when it can be combined with other measurements , like soil moisture, rainfall, wind speed and SDI-12 is precisely the interface that ties all of these sensors together in the field.

uRADMonitor CITY

uRADMonitor CITY is a professional-grade fixed monitoring station designed for outdoor ambient air quality measurement. It tracks ten parameters in total: temperature, relative humidity, barometric pressure, particulate matter at three size fractions (PM1, PM2.5, PM10), and four gas concentrations: ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and carbon monoxide (CO) , each resolved to 1 PPB using sensitive electrochemical cells. A built-in GPS module records the precise location of every measurement.

The device is housed in a UV-resistant ASA Stevenson enclosure rated for continuous outdoor use, with an integrated fan for active air flow through the sensing elements. It supports multiple connectivity options: WiFi, GSM, LoRaWAN, NB-IoT, Ethernet and has been independently validated at the AIRPARIF AIRLAB challenge in Paris in both 2021 and 2023, where uRADMonitor received awards.

How the SDI-12 Interface Works on CITY

The SDI-12 interface is exposed on the GPIO extension connector of the uRADMonitor CITY hardware version 5. A single wire on pin GPIO1 carries the full bidirectional SDI-12 signal at 1200 baud, 7E1 format. No additional hardware is required for short cable runs, but there is a 470Ω series resistor and 5.1V Zener diode provide adequate protection.

The sensor responds to the full set of standard SDI-12 commands and exposes all 24 measured values across six data registers:

• 0D0! — System status: uptime, warmup period, watchdog counter, auto-reboot interval
• 0D1! — Environment: temperature (°C), humidity (%), pressure (Pa)
• 0D2! — Particulates: PM1, PM2.5, PM10 (µg/m³)
• 0D3! — Gas sensors 1 & 2: name + concentration (ppm)
• 0D4! — Gas sensors 3 & 4: name + concentration (ppm)
• 0D5! — Location: GPS latitude, longitude, altitude, speed, satellites, battery voltage

A typical session takes under two seconds to retrieve the complete dataset. The sensor address defaults to 0 and can be changed to accommodate multi-sensor deployments on a shared bus.

A New Dimension for Air Quality Data

SDI-12 connectivity transforms any compatible uRADMonitor unit from a standalone networked sensor into a component that can participate in the broader ecosystem of environmental instrumentation. Whether integrated into an existing datalogger network, deployed alongside hydrological sensors in a watershed study, or used as a calibrated reference point in a smart city air quality grid, CITY can now speak the language that field scientists and engineers have relied on for decades.