Author Topic: Museum Temperature and Humidity Sensors  (Read 1276 times)

e-carlin

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Museum Temperature and Humidity Sensors
« on: March 29, 2017, 01:10:26 AM »
Hi Everyone,
For my senior C.S. capstone project myself and three other guys are building wireless temperature and humidity sensors for a local museum. The museum's main constraints for the sensors are that they are inexpensive and last as long as possible on batteries. After examining many MCU's and transmission protocols (ZigBee, Bluethooth LE, ...) we settled on RFM69W Moteinos. They are inexpensive, have acceptable range, and can be run so that they use barely any power.

In our setup each Moteino is wired to a DHT22 temp/humidity sensor and powered by 3AA batteries (Fritzing only had a 2AA battery object;)). The DHT22 is powered from a pin so that it can be turned off and the Moteino is asleep and won't drawing any current. The devices will spend the vast majority of their life asleep.


Each Moteino transmits its data to a gateway Moteino connected to a Raspberry Pi. The Pi then POSTs the readings to an API on our website. The website has some graphs displaying recent readings and the status of the sensors (battery voltage and time since last transmit). Likewise, the museum staff can donwnload a CSV of all readings for a given date range.

Today we finished wiring up all of the sensors and are going to start a full scale test.


We plan on deploying the sensors to the museum in the next couple weeks so we can give them a run and troubleshoot before we graduate.

The code for the Moteino's, Pi, and website (a Ruby on Rails app) are all available on my GitHub https://github.com/e-carlin/museum_monitoring_sensors.

The sensor Moteino sketch can be found in sensors/pinPowerNode and gateway sketch is in sensors/gateway. We went through a few different wiring schemes and those are available in the other directories under sensors.

I want to thank the community here and Felix for being so helpful and designing such a great product. Myself and my partners had never worked on a hardware project. The knowledge in the forums and on the site was indispensable.

The project is still a work in progress so we are open to any suggestions!

Thank you,
Myself - Evan Carlin (evan+lowpowerlab@carlin.com)
Gabe Lennon (glennon@pugetsound.edu)
Mark Gilbert (mgilbert311@gmail.com
Matt Bogert (mboger@pugetsound.edu)

P.S. Some of us have still not lined up a job after we graduate. If you or anyone you know has a company that could use skills such as these let us know:).

ChemE

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Re: Museum Temperature and Humidity Sensors
« Reply #1 on: March 29, 2017, 02:12:39 AM »
If someone in next year's senior class wanted to build off your work or you had an interest in increasing the battery life of your project, they/you should look into using the Si7021 rather than the DHT22.  You could drop another $5 off the unit price and increase battery life very substantially depending on how often you are sensing temp/RH.  Or you could use some of the work that WhiteHare is doing and convert the systems to small ultracapacitor/PV cell combos and grant them a virtually infinite lifespan.  The latter might be more of an EE capstone than a Comp Sci one but the museum would still love it.
« Last Edit: March 29, 2017, 03:43:19 PM by ChemE »

Felix

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Re: Museum Temperature and Humidity Sensors
« Reply #2 on: March 29, 2017, 08:41:06 AM »
Nice capstone project, glad to see this come to life, thanks for sharing your work!
ChemE - the Si7021 was becoming hard to source and I switched to the BME280 on the WeatherShield, which has all 3 readings included (THP) and is one of the best sensors you can get.
That will sleep in sub uA power also and is tiny compared to the DHT.

ChemE

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Re: Museum Temperature and Humidity Sensors
« Reply #3 on: March 29, 2017, 03:34:25 PM »
Yeah, I really want to play with some BME280s soon.  In fact, we are getting ready to convert 600 square feet above our garage into an AirBnB and I'm going to go mad scientist on the insulation and I'd like an array of BME280s in the wall assembly to measure TH (don't care about P in the wall) to ensure that I can't have mold growth and to track how effective the various insulations are.  I'm getting to the point where I really need to get a reflow oven put together but then that is a whole interesting project in and of itself that I'll probably go crazy on for a while.  Never enough time for all the interesting things to fool with...
« Last Edit: March 29, 2017, 03:44:29 PM by ChemE »

ChemE

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Re: Museum Temperature and Humidity Sensors
« Reply #4 on: March 29, 2017, 03:36:42 PM »
ChemE - the Si7021 was becoming hard to source and I switched to the BME280 on the WeatherShield, which has all 3 readings included (THP) and is one of the best sensors you can get.
That will sleep in sub uA power also and is tiny compared to the DHT.

Forgot to mention that is of course because you buy legit parts.  They are still all over eBay on BoBs but you are correct about naked chips.  I picked up 10 for $4/each shipped which would fit the bill for this capstone project.