Weather Station: Difference between revisions

Revision as of 16:45, 12 March 2012

Description

The project described here is a simple weather station that measures air temperature, humidity, and surface temperature of the ground below the weather station. We want it to:

Run on battery power
Refresh the battery via a solar panel
Sample conditions once per minute
Write data to a text file
Save the data to a USB key
Back up the data to an additional USB key when one is inserted
Use a webcam to take and save pictures of the current conditions

This weather station was designed and built for late winter and early spring conditions, so it is not entirely waterproof (though it could be made so).

Overview

As with any of our described projects, Phidgets takes care of the electrical component design. Still, a project of this magnitude require a time investment in addition to a monetary investment. Designing projects like these is hard.

But the reward is deep - and very real. A full, functional system that you can build to whatever specifications you like... ask any hobbyist and you may see their eyes light up remembering their latest project. Building such things is a special kind of freedom!

We design these application guides to:

Provide template ideas that you can then modify to be your own
Inspire you to try new projects
Give you an idea of the time (both in software and assembly) that this type of project entails

Time: About 6 full days Cost: About

Phidgets

Task	Phidget
Schedule the samples Split and Provide power to devices Run the code	Phidget Single Board Computer
Read surface temperature of ground	1045 - PhidgetTemperatureSensor IR

Power

From the Phidget documentation, we know that the Single Board Computer (SBC) will run at 1.2 watts with no power consumed by devices in its USB ports, and 2.5 watts maximum if all USB port devices are drawing power to maximum specification. Because the power to all sensors and USB devices is included in this estimate, this is what we use to pick a battery and a solar panel.

Although we chose our Phidgets first, and are now designing a power system to support them, the Phidget selection also included some power concerns. With a little forethought, we can guess that the wireless internet adaptor is probably the most power hungry thing that we can plug into a Phidget SBC. A wireless adaptor has two important benefits:

You can download data over the network
You can change code, settings, and scheduling of data gathering as the station is operating

You don't necessarily need an internet connection to use the wireless, as you can connect to it via its phidgetsbc.local local link address.

On the other hand, without a wireless adaptor, the SBC is essentially running autonomously. You can save a lot of power this way, but if the SBC gets into an undesirable state (extreme weather causes it to reboot, a USB Phidget wiggles loose and doesn't properly attach in software, etc) your only options are to either reboot, or add a network connection to log in and change things.

As we do not use wireless here, but do use a webcam, we use an estimate of 2.0 watts to run the SBC.

We would like to have a power setup that will operate continuously, rather than having to replace the battery. This involves solar power, and it also involves knowing something about the expected weather (namely, the sunshine) in the installation location. To take an example as to why this matters, imagine installing a 2.0 watt solar panel into your system. If there were sunshine 100% of the time, this would be a closed, self-refreshing system because the SBC would draw 2.0 watts from the battery, and the solar panel would put 2.0 watts back in.

Your battery amp capacity should be big enough that the SBC can run continuously, with reserves, in times of cloudy weather. Even with a deep-cycle type battery, if your SBC completely drains your battery, depending on the battery type it has a chance of dying completely (which is called bricking) and will lose its capacity to recharge.

Your solar watt capacity should be big enough that in periods of sun it can recharge the battery much faster than the SBC will drain it.

External Structure

Code

Putting it All Together

Future directions

The ports can sample at any time interval up to the maximum data rate of the Interface Kit attached to the SBC.

The Single Board Computer is just that - a computer! So you could

@@ Line 47: / Line 47: @@
 From the Phidget documentation, we know that the Single Board Computer (SBC) will run at 1.2 watts with no power consumed by devices in its USB ports, and 2.5 watts maximum if all USB port devices are drawing power to maximum specification.  Because the power to all sensors and USB devices is included in this estimate, this is what we use to pick a battery and a solar panel.
-Although we chose our Phidgets first, and are now designing a power system to support them, the Phidget selection also included some power concerns.  With a little forethought, we can guess that the wireless internet adaptor is probably the most power hungry thing that we can plug into a Phidget SBC.  A wireless adaptor has a number of benefits:
+Although we chose our Phidgets first, and are now designing a power system to support them, the Phidget selection also included some power concerns.  With a little forethought, we can guess that the wireless internet adaptor is probably the most power hungry thing that we can plug into a Phidget SBC.  A wireless adaptor has two important benefits:
 # You can download data over the network
 # You can change code, settings, and scheduling of data gathering as the station is operating

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