Hi everyone, this is my first post. Hope I've put it in the right place...

I'm in the process of designing a 'solar cooled greenhouse' system for a university project. We're required to make a working prototype of our concepts and I have hit a bit of a wall. To make my project work, I need some form of electronic control and possibly even data logging to make graphs from for our report.

The way the system works is, air passes through a pad which is saturated with a fluid which dries the humid air. The air passes through a second pad which is saturated with water which evaporates into the air thus cooling the air. The air then passes over the crops being grown and then through a second evaporator pad which is used to cool the first drying pad. (I hope that makes sense to most people!)

The system works by using fans to draw air through the system, and pumps to pump the fluids around the system. What we require is a control system that will monitor the temperatures at different locations through the greenhouse, and adjust fan speeds accordingly. While doing this, it would be great if the data could be logged on a file on a computer via a serial port, or even better USB.

Unfortunately, the group is made up of engineering and design students, none of us know a thing about electronics...

Would any of you be able to point me in the right direction of where I would even start to be able to pull this off. I have some basic electronics knowledge as we have done some simple circuits before, one using a small temperature sensor which turned an LED on and off, but nothing this complicated. I also do a fair bit of programming, but in PHP and other similar stuff...

ed

 

How are your collective programming skills? The system will interact quite a bit, so independent local controllers are not going to give good results. Your logging computer might morph into a dedicated microcontroller which actively scans sensors and adjusts the fans, humidity, temperature, sun screens, etc.

Try making up a comprehensive list of the various things that must be controlled, the conditions that affect them, and how they interact. Then you can put together a flow chart for how the greenhouse controllers work together.

That should let you see if a central controller isn't a better approach.

 

You can do it without a microcontroller but I don't suggest that because the circuit will be big and complicated. Thus, you need to use a microcontroller with built-in ADC (analog-digital converter) to read the thermistor value and thus temperature. You can store these values into the memory of the microcontroller and then display them on an LCD display. If you want it to communicate with a PC then things get more complicated. You will need the appropriate software which will be able to communicate with the microcontroller and read these values. If you are lucky you will find one which may suit your needs. If not, you have to get deep into programming.

 

ed;

This sounds like a perfect project for a low cost Arduino development board. This is an open source (hardware and software) development board that uses USB to program your application in C from the free PC IDE software. Once programed the board can be run independently from the PC using battery or small wall wart power module. It has 6 A/D inputs available and 14 digital I/O pins. There are lots if library routines available for using I2C type modules for remote sensors or real time clock modules, etc.

The development boards being open sourced are available from several manufactures and are about $30-40 for the USB version all thought I bought a RS-232 kit version for under $20. You will have to add temperature sensors and figure out how you will control the fans (solid state relays driven output pins should work for on/off control).

Data logging may require adding a storage device depending on how much data you accumulate and how often you will down load it, the built in serial interface allows for communication with a PC via a USB serial for downloading of data.

Anyway here are a few links if you want to investigate the Arduino world:

http://www.arduino.cc/

http://nkcelectronics.com/arduino.html