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TOPIC: Wireless Temperature and Humidity Sensor

Re: Wireless Temperature and Humidity Sensor 8 years 9 months ago #5547

Thanks AndyO.
What I have to do is design a device to monitor temperature and humidity in rooms in an old stately home. There is approx 50 rooms to monitor so keeping the costs down will be a great advantage.
Thanks again for your help
Mark

Re: Wireless Temperature and Humidity Sensor 8 years 9 months ago #5548

  • andyo
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50 rooms - wow. The XBee modules are very easy to use but I'm not sure they're the cheapest solution. As this was a one-off, cost wasn't the most important factor for me.

You could always build one sensor, strap it to a cat and let it wander freely through the house - over time you'll get a reading from every room! Not sure how the cost of cat food compares to XBee modules though...

How will you power the sensors? If they can be plugged into a mains supply then can you use the mains wiring to send the data rather than doing it wirelessly?

Re: Wireless Temperature and Humidity Sensor 8 years 9 months ago #5549

Hi AndyO, do you think you could do an article on how use the MAX756? Just some basic stuff like part selection guide and simple calculations..

I'm looking at using something similar for my sun chaser project, it would be handy to use a similar setup

Re: Wireless Temperature and Humidity Sensor 8 years 9 months ago #5550

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I found the MAX756 pretty easy to use and ideal for a battery-powered app. Happy to help but I'm afraid I didn't do anything too clever - the circuit I used is the same as the sample given in the datasheet with two differences - the inductor should be 22uH and I used 2 x 100uF caps in parallel on the output (C3 & C4 in my diagram).

I used two parallel caps because the datasheet says that the ESR (equivalent series resistance) of the filter capacitor should be as low as possible. By using two caps in parallel you get a lower ESR than just a single cap on its own. The XBee module draws a fair bit of current when it transmits and I wanted a good sized filter capacitor on the output. I breadboarded the circuit and found 2 x 100uF caps worked best so that's what I went with.

When it comes to choosing the inductor, it should be able to handle a current of 1.2A (the one I used was actually rated at 1.0A) and have a DC resistance as low as possible (ideally less than 0.03 ohms). Something like the ones shown here should be ok:

http://www.rapidonline.com/Electronic-C ... 1#techspec

Hope this helps. Have a look at the datasheet, get some parts and have a go - worse thing that can happen is you release some blue smoke! Give me a shout if you have any other questions.

Re: Wireless Temperature and Humidity Sensor 8 years 9 months ago #5551

What do you think of the communication protocol of the sensor?

Re: Wireless Temperature and Humidity Sensor 8 years 9 months ago #5552

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What do you think of the communication protocol of the sensor?
I've tried Andy's SHT.bas module which made interfacing with the SHT11 a breeze (had to refer back to this project as a guide for use)
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