Very useful Pi extension board

I’ve been asked to help create a Raspi solution for an automatic greenhouse (opening and closing the window at first only, that is).
While the computing side of it is fun, my Physics class is aeons ago and I feared overloading a port or something.

The organizer of the PiAndMore conference I attended in Trier this January gave me the tip to look at PiXtend. In case you are looking for a robust Pi working environment, I forward this advice now. Looks really promising – I’ll post updates when I have first results.

Thanks for the tip! Looks really cool and something I have been looking for. Robust I/O is really needed for the RPi when comparing that platform with Arduino.

That doesn’t sound too difficult. You need something like an si7005 temp/humidity sensor and a relay to trigger whatever motor you plan to use to open and shut the window.

The PiXtend does look pretty cool, but probably overkill for most things except maybe robot wars. :slight_smile:

overkill but maybe usefull for someone that needs a lots of I/Os

Yes, but with a certain cable length you need to consider buffer condensers, protect the Pi from the voltage peak that may occur when the motor starts, have to drive to the field where no WLAN is accessible to set the Pi’s clock after a power shortage again and I don’t know what more. The developer is very helpful in figuring out the right configuration for your needs. That’s a bonus I appreciate with my almost forgotten physics basics.

The motor would be isolated by the relay. You just need to size the relay appropriately for the motor’s power supply. If you need to limit the range of motion then a couple of limit switches could be used like on an electric gate opener.

If there is no wlan for setting the time and you want to use clock time as an input you can get a small real time clock board that has a coin cell lithium battery. My first reading of the situation was that you would just use temp and humidity to make the determination. I’m not sure why the clock time would be all that important. I’m not a gardener though. You could also use a photo cell if you wanted something based on day/night, and if rain could get in the window if open, you could also source a sensor to detect that outside the greenhouse as well.

I’m not really sure what cable length issue you’re worried about, but that is most likely a simple matter of making sure the gauge is the right size for the current and voltage you need for the motor. I don’t see any issue from the pi’s side.

This would be a cool project to post some details on when you get it done.

It’s planned a bit more sophisticated, and most of all it should be extendable and robust enough for the not-always ideal working conditions for a device that is only certified for 0 to 40 °C and a humidity below 100%.

For the first step, several inside temperature and humidity sensors are planned, plus a rain and a wind sensor to avoid opening the window when it storms outside. It is not clear yet if the motor will need 12/24V or 230 V. Later maybe humidity soil sensors and a connection to the sprinkler will be added, where the time could be useful so the gardener doesn’t stand in the rain suddenly. And I learned about experiments with camera modules without infrared filter. The University of Trier measures the chlorophyll saturation of plants with them just by taking their foto.

In general I agree with you. Everything should be possible with a pure Raspi and standard modules. The whole thing being planned in a working environment where organic plants should be raised until they are delivered to a project where people can learn to grow their own food over the course of a year, with very limited funds and small staff, demands a solution where I can install an update, click in a few sensor cables into the otherwise finished installation and be sure everything is connected firmly. I wouldn’t dare that on a more or less flying installation that rests on my very limited soldering talents.

And sure, I’ll post updates and details if this project comes into existence.

"PiXtend V1.3 Bausatz - ARTC (Almost Ready to Control) " I was looking for that. Thanks for the hint Ulrich.