Bench Talk

Some of the most challenging yet immensely satisfying embedded projects to work on involve observing environmental conditions. From a personal perspective, environmental monitoring projects are a chance to do something good for mankind. Whether tracking the air quality in a building or measuring the contaminants in a far off lake, embedded systems built to monitor the environment can really benefit our world.

Establishing trends is a useful method in learning what is happening in a system and helping to determine associated root causes. Environmental monitoring tools can provide the prerequisite data needed to make informed decisions about how we interact with and care for our planet. After all, according to famed engineer W. Edwards Deming, “In God we trust, all others must bring data!”

Conversely, environmental monitoring projects can be very challenging from a technical perspective. There are many unique design considerations that may arise depending on the environment. Some of these challenges include:

• Hostile Environments: The reason we monitor many locations is specifically because of the hazards. Those hazards that are dangerous to people can also be unforgiving to electronics. Whether it is chemicals in a factory or inclement weather in the outdoors, embedded systems in these environments need to be rugged.
• Lack of Reliable Power: Sensors used to monitor remote environs can’t always rely on the electric grid. Making devices self-sufficient by generating their own power and conservatively using what they generate is key.
• Communications: Remote locations may be far from telecommunications infrastructure, thus limiting how a device can communicate the data it is collecting.
• Maintenance: Hazardous and remote locations are places where we do not want humans routinely traveling. Thus, devices must be built to minimize if not eliminate the need for human interaction  or to perform maintenance.

The remoteness and the potential hazards involved with the environments we are considering will drive design choices that we might not consider in more consumer-oriented projects. But there are a few design tricks that can be incorporated into environmental monitoring projects to make them more robust. Here are a few things you might want to consider for your next design:

• Alternative Power Sources: Solar panels are the go-to solution for many remote monitoring applications. That doesn’t mean it’s the only or even the best option. There are a family of energy sources known as energy harvesters (sometimes energy scavengers) that transform ambient energy into enough electrical energy to power small embedded projects. They also tend to be coupled with a battery or capacitor to store the energy so the device can be powered even when the ambient source cannot produce enough electricity to power the device directly.
• Ruggedized Enclosures: Run-of-the-mill project boxes won’t cut it in harsh environments. Enclosures must be able to withstand varying temperatures, resist water infiltration, and stand-up to UV radiation.
• Watchdog Timers: Many embedded platforms have a watchdog timer built in. If your platform of choice does not, there are external options available. A watchdog timer is a device that looks for activity on a microcontroller pin at regular intervals. If activity is not detected after a set period (a period you can program in your firmware) then the watchdog timer sends a reset signal to the microcontroller. The idea being that if a microcontroller somehow finds itself in a “frozen” state, it can be reset automatically without the need for a person to press a physical reset button on the PCB.
• Low Power Mode: Embedded platforms have different power modes depending on how much computing horsepower is required. Know the environmental variables you are tracking and the minimal frequency they need to observe. This allows you to put your embedded device in a low power mode in between wake states needed for data acquisition. This will let you get much more mileage out of your battery.
• Storage: Acquiring data is half the battle. It eventually needs to be analyzed on a computer to be of any use. That means the data needs to get out of the embedded system and communicated to a server or desktop computer. However, the communications channel can sometimes be unreachable. Don’t let the data collected during a communications outage slip into the ether. Using an external storage solution, such as an SD card, is a simple way to implement a data backup solution.
• Beyond WiFi and Bluetooth: Many popular communications protocols we rely on in our daily computing life, like WiFi and Bluetooth, are great for relatively short distances. Notwithstanding a few tricks to boost the distance of WiFi, these technologies may not be the most reliable for environmental monitoring applications. Cellular network-based communications modules or satellite phones may be required to transmit data from remote sensor nodes. If you are building out a wireless sensor network of many devices, it might be possible to implement a mesh network topology that lets devices pass data to each other until the data reaches an Internet-connected node that can communicate the sensor data externally.
• Sensor Drift:  It’s no surprise that many devices and tools require calibration from time to time. For devices we touch frequently, this may not be a big deal. But for wireless sensor networks that are not easily accessible, it is best to design in some capability to account for and correct sensor drift. The easiest way to do so is to include multiple copies of a sensor and have the software interpolate a value based on averaging the different sensors. While more complex solutions are being researched to combat sensor drift, for now realize that sensor drift exists and that recalibration may be required from time to time.