Part 1 - Overview & Initial PIC Circuit
I’m Dave Ek, NK0E, and N2APB has graciously granted me some space on his regular Digital QRP Homebrewing web pages so I can share my latest project with you as it develops. I’ve been a ham now for about six years, and I’ve been playing with the PIC16F84 microcontroller for three of those years. My first design was a system of digital setting circles for an astronomical telescope using rotary encoders and a serial link to a PC (see http://home.earthlink.net/~digicircles). More recently, I designed the Serial CW Sender, a circuit that allows you to key your CW rig via contesting software running on your Palm PDA. The Serial CW Sender was featured in the July 2001 issue of QRP Quarterly, and you can read more about it and the accompanying software at http://home.earthlink.net/~golog/.
Lately I’ve been experimenting with packet radio and APRS (Automatic Position Reporting System). APRS is quite different from your typical packet BBS. Instead of connecting to a single BBS system, you use APRS software (like WinAPRS or UIView) to periodically beacon your station position on the standard APRS frequency (144.39 MHz), and to plot on a map the positions of other APRS stations heard. Some APRS stations act as digipeaters so that your beacon (and others) is heard over much wider areas. It’s typical for my APRS software to show locations of stations all over the state and also in neighboring states. In addition, some stations act as internet gates, rebroadcasting position beacons onto the internet where they’re heard and displayed at http://www.findu.com/. It’s pretty neat to see my station beacon, sent from my station as RF, show up seconds later on the internet!
“So what?” you say? Good question. It turns out that APRS packets aren’t limited to position information. I can send messages, send short emails (I can do this through satellites or even the International Space Station), and even broadcast weather conditions using APRS. Weather, of course, is especially near and dear to the hearts of many hams, since many of us are active as weather spotters during storm season. It occurred to me that being able to automatically beacon weather conditions at my QTH would be especially cool. But alas, I had no weather station, and I couldn’t see myself spending several hundred bucks to buy one.
But hey, I could design and build a weather station, again using a PIC microcontroller as its brains. This is the kind of project that I live for. I know that I can make it work, but I’m not exactly sure what it’s going to look like when it’s done. You know what I mean - it’s full of opportunities to learn. After all, it’s the journey, not the destination, right?
So, over the next few issues, N2APB has invited me to use his column to share my progress as I tread this path. I’ll do my best to include enough information so you can follow along if you also want to end up with a cool homebrew weather station. You’ll see that there are many QRP applications both for PICs and also for the circuitry we’ll be using to interface our weather sensors. You can even tag along when I venture down those blind alleys and dead ends — after all, we learn as much from our mistakes as our successes. And rest assured that, as I write this, I really don’t know how this project is going to look at the end. I only know that it’ll provide some great entertainment over the next several months.
So, let’s get started!
It’s generally good to know what you want your end product to do when you start a project like this. Quite simply, I want to be able to measure the weather conditions at my QTH, record them on my PC, and then broadcast them periodically using my APRS software and station. In particular, I want to be able to measure temperature, relative humidity, barometric pressure, wind speed and direction, and rainfall. I also want to be able to easily control the time interval between...
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