DIY indoor thermometer and moisture meter


Raj designed an open hardware DIY indoor thermometer and moisture meter. It’s based on the PIC16F688 coupled with the DH11 temperature and humidity sensor. The 7-segment display has auto brightness correction depending on the lighting conditions.

This project is about building a microcontroller-based digital room thermometer plus hygrometer that displays temperature and relative humidity on 4 large (1 inch) seven segment LED displays which adjust their brightness level according to the surrounding illumination.

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  1. Neat project, but I have to disagree with the open hardware designation, as the schematics and source code are (currently) all rights reserved.

  2. Like most Maxim parts, the MAX7219 is pricey and difficult to find (DigiKey MAX7219EWG, $13.57 in unit qty. but I have seen variants for around $7 to $8 USD ea.) I have no problem using it for one-of quick projects, but the use of this part should have relegated this project to the “Meh” bin instead of earning it posts all over the DIY Blogosphere. With the PIC16F688 the LED display could have been Charlieplexed while still leaving enough pins for both an indoor and outdoor senor. This of-course eliminates the MAX7219. There’s plenty of PIC LED driver stuff out there, which make the job easier.

    @Cov, I don’t think there is a problem with possessing a Copyright while specifying an Open-Source License. I may be wrong, but I think Copyright and License are two related but very different things. The Copyright Holder may specify the License. For example I hold the Copyright on a piece of software but specify an MIT license.

  3. The MAX7219 are expensive at regular retailers, but at eBay they are only about $1 each.

    But charlieplexing is a good alternative to it as long as the display is of a hi-brightness type….

    1. Hi @Matseng or other DP regulars: Have you tried those Ebay 7219?. I was going to buy some once I had accumulated enough other part needs to make a worthwhile order. I am very leery/gunshy over ebay parts as I figure they are used “pulls” or worse, fake and non-functional.

      1. @eff Nah, I haven’t tried them, but I imagine that as long as your’re getting them from a established ebay seller they would work just fine – or else the ebay rating system would have taken care of them a long time ago.

        A “pull” wouldn’t bother me too much, it’s not like they are wearing out over time, and can I get as many as I want for 1/15th of the cost for a new part I would accept it as long as they are not broken electrically or mechanically.

        You really don’t need to wait for a accumulating a big order, these guys sells like 5 for $4.99 shipping included so it doesn’t matter you do a small or large order. The shipping costs will be the same – zero :-)

  4. @Matseng I know I could afford to lose $10 – $20 on a speculative purchase, thats not the point. I really hate giving money to crooks and scammers because it only encourages them to multiply. 10 bucks from me, 20 from you and a bunch of others and they start to get rich. I don’t trust the rating systems, especially on alibaba, Taobao its all corrupted. Once one seller listing name is burned they just create another. Pulled parts are often ESDed or heated to death or near death which is even worse because intermittent failure wastes my time.

    I have heard that in china one of the attitudes buyers take is that they are going to get cheated a certain percentage of the time and they just shrug and accept and treat it as some kind of game or sport.

    1. Eh… I thought we were speaking of ebay – not Alibaba/Taobao. If you have a seller with thousands of transactions and 99.9% rating on ebay I’m rather confident that he won’t sell you broken crap or else he wouldn’t have a 99.9% rating. It takes a while to rack up thousands of transactions…

      But if you are getting stuff from a seller with 5 sales and a 90% rating all bets are off of course.

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