Tuesday, 15 May 2012

Remote temp. sensing with GLCD and Jeenodes

It's been a while since I purchased the Jeenodes, the original intention was to get them talking to each other using the wireless tranceivers and the graphics display board to dosplay the received temperatures.
Anyway, life happens and I got distracted and they were put in a drawer .... time went by and I got interested again.
So I've now managed to get the Graphical LCD (GLCD) working and displaying the temperatures and other data from the remote transmitter.
The plan is to have a Jeenode mounted in a waterproof box outside, monitoring the outside temperature and also, using a magnetic reed switch, monitoring the status of the side gate.
So far I've managed to get a Jeenode sending the data from two DS18B20 digital temperature transmitters once every second, then I was able to get the GLCD from Jeelabs to display the temperatures in a normal font.

I decided that the fonts need to be a bit bigger, so it could be easily read from a short distance, this wasn't as easy as I thought it would be, it requires a lot of thought about how many pixels are required to display the temperature.  One disadvantage, albeit a small one, I found with the new library that allowed large fonts was that it didn't clear unused pixels when a new character was drawn over the top of the old one.

A quick visit to the Jeelabs help forum soon pointed me in the right direction, you have to draw a white rectangle over the characters just prior to writing the new ones to the screen, I thought this was a bit of a pain but in reality it's quite simple to add that line prior to any text you send to the display and it isn't noticeable as flicker.  The tricky bit is counting the pixels used in the width across the characters to ensure the rectangle only covers the temp and nothing around it and choosing the font was a bit of trial and error picking the various ones available as I couldn't find a printout of what all the fonts would look like and there are a lot of fonts.
Now I've just got to find a suitable box to put it in, sort out a battery and read up on getting the sketch to consume as little power as possible, I'm waiting for the single AA power board to arrive from Jeelabs.

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