The Blog of Ian Mercer.

Humidity Sensors (DHT11, DHT22, AM2320)

The DHT11 and equivalent humidity sensors can be connected to an Arduino or ESP8266 easily to provide humidity data to a home automation system. The local pull-up resistor is critical: reduce it to ensure you get a reliable digital signal from the device. Connecting them over a long distance has proven tricky as there is a lot of noise on the data line. Even with the correct resistors and short runs I find they still provide bad data occasionally (drop or add a bit) so I also feed them into a simple filter: keep the last 5 values, sort them by value and then pick the middle one.

I use humidity sensors in the bathrooms to automatically turn the fan on and the heating element behind the mirrors when the bathroom becomes steamy.

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Home Automation Sensors

An overview of the many sensors I've experimented with for home automation including my favorite under-floor strain gauge, through all the usual PIR, beam and contact sensors to some more esoteric devices like an 8x8 thermal camera.

Ian Mercer
Ian Mercer

Filtering techniques

Filtering raw data is essential for a reliable home automation system. Here are some of the many ways you can filter sensor data.

Ian Mercer
Ian Mercer

Bluetooth Sensing for Home Automation

Bluetooth sensing for home automation is a great proxy for people counting as it can detect and locate each cellphone in the house. iBeacons attached to tools, cars and pets can provide a 'find my anything' feature too.

Ian Mercer
Ian Mercer

Gas sensors

Gas sensors come in many different flavors including CO2, VOC and particulate sensors.

Ian Mercer
Ian Mercer

Light sensors for Home Automation

Having at least one light sensor is critical for any home automation system that controls lightng. Lights need to be turned on when it's dark not at specific times of day, especially here in Seattle when it can be dark and cloudy at any time of day.

Ian Mercer
Ian Mercer

Microwave Doppler Sensors (RCWL-0516)

Microwave doppler sensors can be found in some alarm sensors but there are also available very cheaply as a separate component. They offer exceptional range but suffer from false triggers requiring a probailistic approach to people sensing.

Ian Mercer
Ian Mercer

Optical-beam sensors

Optical-beam sensors are reliable and can cover a long-distance such as across a garage or aisle-way. When they include multiple-beams they have good false-trigger rejection.

Ian Mercer
Ian Mercer

PIR Sensors for Home Automation

PIR sensors are cheap and easy to use but they suffer from slow response times and low repeat rates.

Ian Mercer
Ian Mercer

Strain-gauges

Strain-gauges are my top-rated sensor for home automation because they are invisible, reliable and can be tuned to detect people and ignore pets.

Ian Mercer
Ian Mercer

Temperature sensors for home automation

Temperature sensors I've experimented with for home automation.

Ian Mercer
Ian Mercer

The Grideye 8x8 camera sensor

Experiments with an 8x8 IR camera for privacy-preserving people detection using cameras.

Ian Mercer
Ian Mercer

CCTV Cameras as Home Automation Sensors

CCTV cameras are an option for detecting people but within the home there are privacy concerns that need to be addressed.

Ian Mercer
Ian Mercer

Pressure Sensors for Home Automation

Pressure sensors can detect HVAC system operation and could potentially detect clogged filters.

Ian Mercer
Ian Mercer