Disk Farm Cooling
In fact the first use of this project was to drive some airflow through an Ikea coffee table reworked to hide a Barco projector.
The fan controller uses the analogue output at channel 0, this channel can be driven from the state engine that takes its trigger from the temperature sensor.
In this case we're going to use standard 12V fans, you can use fans up to 1.0 Amp with the circuit below
This circuit is known as an 'Emitter Follower' and its a near 1:1 voltage amplifier. Fans do not have a linear air output against voltage supplied since at lower voltages the fan blades will not turn. This is not a problem for the WebBrick since we can adjust these using the set points.
Here's a photo of the above circuit built onto Vero board:
Note the use of the heatsink, this is not needed for small fans, but is needed for fans that take more than 300mA, or if you are using multiple fans.
Configuration
If you refer to the WebBrick manual you'll find that there is a 'Fan Controller' mode. This mode sets the Analogue Channel 0 to Set Point 0 at target temperature and indexes the Set Point as the temperature increases. If the target temperature was 20 deg C then the behaviour would look like:
| Target Temp |
TT + 1 |
TT + 2 |
TT + 3 |
TT + 4 |
TT + 5 |
TT + 6 |
TT + 7 |
| Set Point 0 |
Set Point 1 |
Set Point 2 |
Set Point 3 |
Set Point 4 |
Set Point 5 |
Set Point 6 |
Set Point 7 |
This configuration would look like
Note that actions are set to 128, this sets bit 7 of the Temperature Sensor state engine and enables fan controller mode. This is not an exclusive setting, the high, low and channel actions can still be used.
Because fans will not start to spin their blades until a decent voltage has been reached, this characteristic has to be configured into the set points. Here's the example with a 200mA 12V fan:
In operation, the home page currently looks like
The more observant of you might notice that we do not announce Fan Controller mode on the home page, we ought to, and will get round to fixing it.
And finally for a bit of fun, here's a bench example of a WebBrick controlling its own temperature; You can just see the fan spinning. The example screen shots above were taken from this live example:
