automating, building and graphing the world


Rabbit Microcontrollers

Rabbit, an odd name for a microcontroller if you ask me but there you go....

Rabbit microcontrollers from Zworld are available in a number of guises, most interestingly from my point of view with embedded ethernet. This opens up a whole raft of possibilities and my first proper project is to build an ethernet capable temperature monitor.

Recently I'd found a website advertising ethernet capable temperature monitors. They looked exactly like what I wanted to be able to measure temperature in any room with a network connection.. The only problem was the price. The were asking 260 GBP for the main unit and a futher 40 GBP for a temperature probe! So essentially 1 complete unit would cost 300 GBP.

I'd been 'playing' with a Rabbit RCM 2200 for a while getting used to it and decided that I'd give it a go. In the first instance I was going to be fairly inefficient in my use of equipment, connecting the Rabbit to a Basic Stamp and connecting a DS1620 to the Basic Stamp (in theory a number of sensors could be connected to the Basic Stamp and the information fed back to the Rabbit). Looking at the Raw costs for these and adding a little extra for small parts like resistors I calculated that I could probably make an ethernet temperature monitor for 111 Euro, about 66.6 GBP!!! How about that for a saving!

This page will document that process...

18 Feb 2003

I've got my first version completed on breadboard and it works! The hardest part was reading the connections off the Rabbit development board. I'm sure that even if I'd used an electron microscope they would have been hard to read. As luck would have it I made an ever so slightly educated guess and was right.

The Basic Stamp is now connected to the Rabbit via the Rabbit's serial port B.

There were some minor problems with bounds overflow in my C Code but that has been fixed. I'm not 100% happy with the output from the Basic Stamp. The temperature reading isn't showing the 0.5 degree steps, just whole degrees. I've updated the code on the Stamp but the Rabbit isn't happy. I'll have to rewrite the serial input routine...

I've managed to solve this problem and now the 0.5 degree changes are reported - hurrah!

I have been thinking about this a little more and it seems a bit of a waste not to add other sensors to the setup. I'm thinking about a light sensor, motion detection and perhaps humidity too. I'll need to look at what I have and what chips I can get hold of.

Added a photo resistor so now it knows when it's light or dark...Above is the current setup on breadboard. Within the next few days I'm hoping to move it to stripboard and into a casing.

I finally got around to moving from the breadboard to a prototype board. It's been running without any problems for a solid 24 hours now, so I think it's stable.

Ok, so it wont win a beauty contest, but it is just a prototype. I'd like to at least half the board area used which would be easier if I had some circuit boards made up. Sadly the cost of doing that is quite high so it wont happen in the near future. I've moved the DS1620 (temperature IC) off the board attatching it via approximately 1m of cable. This allows the main box to be hidden and the probe placed where it is needed. Note in this version of the board the dark/light detection is absent. This is purely because I have been tsting the board as I add the components, it should be back shortly. Ultimately the Basic Stamp needs to be replaced by a PIC of some sort.

A Few people have pointed out that the Basic Stamp (and even PIC) are redundant as the Rabbit can handle all the functionality. However, the Rabbit's role is purely to add network connectivity, nothing more. Since the only ethernet boards for the Basic Stamp currently retail at around $75 (USD) the Rabbit is a bargain at less than half that cost. I also wanted to be able to expand the circuit, adding more sensors. The more the Rabbit has to do the less likely it will be that it could poll all the sensors and still respond to status requests in a timely manner. The next additions will probably be proximity detection. I have a number of Qprox chips for this purpose and have managed to get them detecting from over a 1m.