- Sat Feb 23, 2008 9:52 pm
#43341
It all depends on what what sensors you have, what processing you need to do with the data gathered by the sensors, and where that data will be processed. The two systems that I built were quite different. The first one uses multiple sensor modules incorporating a PIC 16F88 to read temperature, humidity, and rain amount, sending the raw data to a PC for processing. The second system uses the 18F series on both ends (no PC) since I need to do more processing on the sensor side as well as the receiving end. Also on the receiving end, I am driving a LED display which requires a higher I/O pin count.
Here are some questions to ask yourself:
1) What sensors will be supported and what are the number of I/O pins required to support them? If you have basic sensors, something along the lines of 16F88 might fill the bill. Since I wanted to drive an LED display on the receiving end, I opted for a 18F452.
2) How much processing will the PIC have to do to read and prepare the data so that it useful? My barometric and humidity sensors require a number of calculations to apply correction values for changes in temperature. The extra memory and I/O pins in an 18F252 came in handy as I could use my compiler's floating point library to simply things on the receiving end and also incorporate more sensors.
3) On the receiving end, do you want to use USB to connect to a PC? If so, you will want to look at the 18F2550/18F4550 or similar chips in that family.
4) The XBee runs at 3.3v. Will you run the PIC at 5v and use level conversion between the XBee module and the PIC, or will you use a PIC that is rated at 3.3 volts?
These questions should get you started.
Ralph
