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Remote Units implementation, the hardware

This post is part of the Temperature monitoring project.

The Remote temperature units are the nodes that collect temperatures from sensors within a given place.

Given the choice explained in “Initial considerations” article, those units send periodically measures to central management site.

Let now go more deeply into the hardware details of the remote units.

I have to apologize about the wording, but from an HW implementation and coding perspective, those units where considered as “central node” within a given placeā€¦ I admit that it can be a little confusing related to the “Central Server” described earlier. So, you’ll see central node in the code and bellow text.

As briefly said before, the hardware implementation of both central node and “home made” temperature sensor is based on Jeenodes. Those boards are an alternative implementation of Arduino with an embedded 433 or 868 MHz RF transceiver (yes, transceiver: it can receive and transmit), sold as a kit.

I found those modules highly interesting because:

  • They have this RF extension OOTB, with an operational Arduino library. I already used those RF modules (this is RF12 units) in another project based on a PIC microcontroller, and believe me, making them working was a headache, with very few resources on internet dealing on that. So, I found wonderful to have both HW and software device management ready!
  • There are very small.
  • They integrate magically (as easy as playing Lego) within a fairly impressive list of other modules.
  • They are affordable.

So thanks very much to their designer, Jean-Claude, who makes that possible.

You can have a look at his site jeelabs.org (but there is also a chance that you come from this site if you are here!).

Coming back to description, the central node is made of:

  • A JeeNode. Upon the different versions, I choose the 868MHz one. See jeelabs.net/projects/hardware/wiki/JeeNode for details
  • An Ethernet Arduino compatible card, the Ether Card that you can see here: jeelabs.net/projects/hardware/wiki/Ether_Card. This card is using the ENC28J60 chip which is not the best one on the market, but has the big advantage of being very cheap, and however, the lack of advanced features found in competitors chip was not at all a problem for this application. By Arduino compatible, I mean the library that comes with it is adapted from one of the Arduino community libraries with very slight changes. I had also to make my own changes to this library to adapt to this particular project. More on that in a next post.
  • A “Carrier Board” which can be seen as the “mechanical & electrical glue” between several modules. You can get it along with a nice box within which everything fit perfectly well. See the pictures bellow to get an idea on that. This board is here: jeelabs.com/products/carrier-board

The Jeenode and EtherCard:

jeenode ethercard

The 433 Mhz receiver, ready to be plugged on Carrier Board. This module holds also a signaling LED and the connection for the local DS1820 temp sensor:

433rx

Now everything assembled:

carrierall

All together inserted into the box:

boxopened

And the final result:

box

And here is the diagram:

centralnodediagram

Next post will detail software implementation.

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