Categories:

Atmospheric (Temperature/Humidity/Pressure)

• Bosch recently released the BME280 sensor, following their line of popular barometric pressure sensors like the BMP085. The BME appears to integrate temperature, humidity, and pressure into a single low-cost sensor. Sparkfun and Adafruit have breakout boards for about $20.
• Note: A continuing issue that I've experienced when using atmospheric sensors is that the device they're connected to tends to warm them up, and make at least the temperature readings inacurrate. Thermally decoupling these from whatever device they're connected to is non-trivial and challenging.

Magnetic Fields

• Ted Yapo evaluted a number of magnetic sensors for his magnetic field scanning project, and found the Melexis MLX90393 3-axis magnetometer to be a clear winner. It has a much larger dynamic range than many other sensors, and also exhibits a saturation behavior in large fields, where as the popular HMC5883L apparently does not exhibit this behavior. This is a relatively new part, and is very inexpensive (about $2 each). Melexis has an evaluation board, but folks like Sparkfun and Adafruit haven't made a smaller breakout for this one yet.

Non-contact temperature/Thermal Imaging

Non-contact temperature:

• The Melexis family of sensors (like the MLX90614) have been the standard non-contact temperature sensor for many years. These are beautiful sensors, tend to have extremely detailed datasheets, and come in a variety of options including voltage and field-of-view. Easy to come by, many tutorials/drivers for various platforms. They tend to be about $10-$25, depending on the model.
• TI has a new series of thermopile sensors similar to the Melexis sensor, including the TMP006 and TMP007. The TMP007 appears to perform the temperature conversion internally, simplifying use. The field of view is quite large (~90 degrees), where the Melexis line has more options for field of view. Adafruit has a TMP007 breakout. A breakout tends to be around $10.

Imagers:

• The FLIR Lepton is a small thermal camera module with an 80x60 resolution for about $300, which is a really enabling price point. Sparkfun has a FLIR Lepton breakout , and example software has been written to work with the Raspberry Pi. When I used this there were some reliability issues, and odd resolutions (e.g. taking the camera out of the socket *while running*). The FLIR Lepton appears to be used in many products that interface with smartphones to provide low-resolution thermal imaging capability.
• Melexis also has a low-resolution option, the MLX90621, which is a 16x4 pixel array with an I2C interface, for about $50.
• Panasonic has the GridEye range of sensors, which is another low-resolution imager option at 8x8, also has an I2C interface, and seems to be about $25 in single quantity. The temperature range appears to be lower than the MLX90621. When I tried to order one from Digikey for evaluation, it required odd paperwork with export restrictions, so I did not pursue it further.

Gas Sensing/Atmospheric Particles

• Bosch appears to be extending their BMP280 temperature/pressure/humidity sensor with the BMP680, which will also include an indoor volatile organic compound (VOC) gas sensor.

Air Quality/Particles:

• An article in Make Magazine, Air quality sensors: How good is good enough? compares two inexpensive sensors with a professional instrument, showing generally good agreement in specific cases, and outlining some of the issues in gas sensing.
• The Shinyei particle sensors appear to be inexpensive optical-based sensors, and are discussed in the Make article. They're also appear to be a little bulky for handheld devices (~5x6x2cm), so projects with these appear to make desktop systems.
• The Sharp GP2Y1010AU0F appears to be similar to the Shinyei sensor, and is of a simliar size. This is available from Sparkfun for about $12, though one of the comments mentions they can be found on eBay with wiring harnesses that simplify connection.
• The Maxim MAX30105 is a new sensor that appears to be similar to the above two air particle detector sensors, but is extremely small, and has three integrated LEDs instead of one or two, and an I2C interface. It appears to be being marketed for smoke detection applications, so it's not clear if it can do the PM2.5 air quality measurements that the above two are used for. If it could, that would be extremely useful.

Gas sensors:

• General note: I've largely avoided the heater-based gas sensors in the past, as they appear to be relatively bulky, tend to require plenty of power, and (most importantly) tend to require calibration for use. There currently don't appear to be many digital options.
• Sparkfun has several gas sensors. There also appear to be inexpensive multipacks on Amazon.
• The MiCS family of sensors are low-profile gas sensors that come in a variety of configurations, and appear to solve many of these issues (such as size), but still require calibration. Adafruit has a breakout for one of these that is sensitive to VOCs, for about $10.

Inertial Measurement Units (Accel/Gyro)

• Invensense was one of the first in this space, and has solid options. The MPU-9250 appears to be the latest 9-axis offering, with 3-axes each of acceleration, gyro, and a compass magnetometer. Sparkfun has a low-profile breakout for about $15.
• Many, many other options depending on specific cost, performance, and size constraints.

Distance

Ultrasonic

• MaxSonar has a great line of compact ultrasonic distance sensors with a variety of range and resolution characteristics, and a variety of interfaces (RS232, analog, and pulse width). These tend to range between $30-$50.
• Many models of larger ultrasonic sensors exist with separate transmitter and reciever elements. Sparkfun has such a sensor for about $4.

Light/Lidar

• There are a number of optical sensors that have a decent range, but many of these appear too large/bulky for a handheld unit. Robotshop has many examples.

Spectrometers

• The Hamamatsu microspectrometer family are extremely small (~2x1x1cm) miniature visible spectrometers, and a NIR option is available, though larger. The spectral resolution is approximately 15-20nm. These are compact and wonderful devices, and are approximately $200. GroupGets appears to be one of the easiest ways to purchase small quantities.
• Hamamatsu has also developed a miniature Fabry-Perot spectrometer in a TO-5 can, with a spectral range of approximately 1550 to 1850nm.

Radiation

• The Radiation Watch Type 5 detector is an exceptional radiation sensor that's compact, able to be powered with batteries, and has an extremely simple interface that can be easily connected to most microcontrollers. I have used this sensor extensively, and it's also possible to increase it's sensitivity with some modification, by adding an external comparator. It also appears to be able to discern at least some energy-level information from the detections, enabling some crude spectroscopy. These are approximately $70.
• Teviso has several small radiation sensor modules that appear to be also based on silicon PIN photodiodes. From my experience with the Radiation Watch Type 5 and looking at the Teviso datasheet, I believe the Type 5 is more sensitive.

UV

• Many small photodiodes are available that detect ultraviolet radiation, and may be suitable for calculating UV index. An example is the SI1145 UV/IR/Visible sensor, which has an I2C interface. A breakout board is available from Adafruit.

Cameras

• Cameras are extremely high bandwidth sensors, and it is extremely technically challenging or functionally intractible to interface these to most microcontrollers. The Raspberry Pi and associated camera module is one of the easiest ways I've found to interface a camera to a project, assuming that the Raspberry Pi is small enough to be used as the underlying controller.

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