Ham Arduino sensors measure almost anything. And quite easily. As a result, you can have fun with a staggering number and variety of cheap sensors.
Makers love home automation and Internet of Things projects. Sensors measure the state of the environment. You can measure temperature, light, and sound with $2 sensors. For a few dollars more, you can respond to motion and force. Also, there are sensors which easily measure voltage and current.
It seems like many folks start off with the DT11 temperature and humidity sensor. Then, makers just need a bit more knowledge to build home automation including entry alarms, motion detectors, sound activated light switches, and so on. Here is a summary of the most popular sensors.
Arduino sensors can be digital or analog. Analog sensors normally provide a variable voltage which can be measured by the analog-to-digital converter built into Arduino. Digital sensors convert readings to data. Many sensors come in I2C or SPI versions. I2C is a two wire bus. Originally designed for inter-integrated circuit communications, the wires carry a clock signal on one and data on the other. The Serial Peripheral Interface bus is a four wire synchronous communications approach. Both are short distance interfaces. However, the benefit of I2C and SPI is the ability to run multiple sensors on one connection, where each sensor has a different address. Arduino has hardware support for both I2C and SPI, as well as built in libraries which make them easy to use.
Ham Arduino Sensors for SWR Meters and Antenna Analyzers
Popular station accessories are one place to start with ham Arduino sensors. These include digital SWR measurement and even complete antenna analyzers. Arduino sensors will easily read voltage and current from a directional coupler or SWR bridge. If you add a digital synthesizer like the AD9850 and a TFT display, you can built a complete antenna analyzer for a few dollars.
If you want some hand holding, the ARRL book Arduino for Ham Radio has many projects like these that you can use as-is.
Coming up next, we will shift from inputs to outputs, specifically displays.