Friday, December 18, 2009

Simple Displays and Homecamp

As part of a quick hack for the homecamp Christmas party competition, I put a few (42) different coloured LEDs onto a bit of stripboard - in the shape of a Christmas Tree. The LEDs were clustered into groups so that different parts of the tree could be individually driven.

As it was a 2 hour mega-rush-hack my addressing scheme wasn't the best thought out, but I did have the means to light up each of the tree branches individually, light up the star on top, plus the pot and stem as separate items. Having wired it up to the digital outputs of a spare Arduino and hacked a few lines of code to animate it, I was struck by the simplicity of it and the effective way that it could be used to convey simple information. It certainly comes alive after dark, with the previously almost invisible pea green LEDs contributing to the effect. These were a bit of a mistake - but I didnt have enough of the brighter blue-green ones and even connected in series it shows how efficient the blue-green ones are by comparison.

The green branches could be used in a sort of bargraph manner to show rising temperature for example, or as it was a Homecamp party, using the segments to show trends of energy usage would make a very appropriate application for it.

This sort of display is very easy to drive from a few lines of code, and is ideal for applications where numerical information is unnecessary. If this was a room thermometer or thermostat, for example, which progressively lit up over the temperature range 16 to 24C, a quick glance at it would be sufficient to tell you whether the room was on the cool side, just right or over heated. The nature of the display is that it's easily visible at the 3 to 4m range, which is good for most peoples room dimensions - and it doesn't mean you have to get up and peer at some tiny LCD thermometer digits to get an idea of room temperature. LEDs are cheap and easy to use - the whole thing could be built for under a pound, add a microcontroller, and possibly my micropower 433MHz transeceiver - and you have a wireless visual thermometer which can measure the room temperature and chirp out boiler on and boiler off commands to the 433MHz thermostat.

With a knowledge of the current cost protocol, it could be used to display household power usage - possibly rewarding you by lighting the star on the top of the tree when you are an "energy star".

Other uses are as an annunciator device to inform you that some event has happened - such as a distant relative logging into a chat program for example, or as a visual reminder, that something needs doing.

Whilst christmas trees may be seasonal this week - they will be somewhat forgotten about in a couple of weeks, but the concept of using a brightly animated LED display to convey trends or events is a lasting one.

A very short clip of the tree, with simple flashing firmware is on youtube:

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