Solar powered temperature sensor (multi sensor)

[daveyk]

This is my first Raspberry Pi project.

The goal is to make a solar powered wireless temperature monitoring station. The data will be copied to a windows PC for processing.

It is very similar to http://www.raspberrypi.org/phpBB3/viewt ... 37&t=24856 but the temperature sensors will not be wireless.

I am thinking of using the following:
Raspberry Pi Model B (I am using a model B as I may add things, or repurpose this in the future.)
3 temp sensors, they will be connected up to 2 meters away from the Pi;
A solar Cell;
UPiS: http://pimodules.com/
WiPi: http://www.element14.com/community/docs ... assy-group

To keep the power consumption low, I would like to boot the Pi every 10 minutes and let it run for a minute to get data, then shut the Pi down. Eg:
Turn the pi on;
poll the temp sensors;
copy temp data across wifi to windows PC;
Turn off;
Wait 10 mins, repeat.
To achieve the turn on / turn off function I was thinking of using a the UPiS. The biggest downside I can see for this is the initial cost of the UPiS unit. Is there a cheaper alternative? (I was looking at SODAQpi, but it isn’t available yet? Not sure on pricing? http://www.raspberrypi.org/phpBB3/viewt ... 63&t=60440)

I am in Queensland, Australia, so even during winter I get about 10 hours of sunlight, and with cloud cover, my expectations are to be able to power the device for 48 hours without charge. The UPiS manual says it will provide 5 hours without charge, so If I’m powering the Pi for 1 minute in 10, then I think this will be ‘close enough’ for me, unless I’m missing something.

The WiPi will be connected to the Pi via a 2 meter USB cable. Will this distance USB cable cause issues with power?

The Temperature sensors will be DS18B2. The 3 sensors will be 5cm, 1 m and 2 m away from the Pi. Will I be able to get 3 separate measurements from these? Or will it somehow all be 1 measurement? According to http://www.cl.cam.ac.uk/projects/raspbe ... ndix-three the sensor will log with a serial number of the sensor. Does this mean each of the 3 sensors will have a different serial number?

Any suggestions on an OS?

Since this is my first Pi project, can anyone advise on anything I am doing wrong, overlooked, can simplify, etc.

Thanks

[FLYFISH TECHNOLOGIES]

Hi Dave,

To keep the power consumption low, I would like to boot the Pi every 10 minutes and let it run for a minute to get data, then shut the Pi down.

I believe that RasPi is overkill for your task of reading 3 temperature sensors each 10 minutes...

This task should be delegated to a tinny microcontroller. As a result, you can save on solar power components (smaller cells and accu capacity). You also don't need external power on/off timer, because this circuit would be constantly on; most of the time in sleep mode, of course.

If you'd like to use RasPi anyway (and this project is just an "excuse"), then you might use it for data processing.

To answer some of your questions anyway:
- (certified) USB cable for WiPi can be up to 5m long,
- 2m of wire between to the sensor is not a problem. If you have mixed feelings, decrease pull-up resistor value from 4k7 to 3k3 or so. Additionally, add 100nF ceramic capacitor close to the sensor between Vcc and GND pins. (I supppose you're not using it in parasite power mode.)
- yes, each sensor has unique serial number, burned permanently during manufacturing process,
- any OS.


Best wishes, Ivan Zilic.