NAVIGATION

North Pole Loop
Sharon, Idaho
Bear Lake, Idaho
National Forests
Weather
Currently
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Weather

It was only a matter of time before this project would merge with electronics and software development. I'm working on a weather station. The reason I am interested in the development of a weather station is because the closest place I could find to report weather is Montpelier or possibly Paris. While the snow is deep and the winters are cold in both of those areas, I learned that Sharon/Liberty has a bit of its own micro-climate. Apparently there's something about the valley that Sharon and Liberty are in, which seem to trap and force out a lot of moisture during the winters.

 
The biggest challenge to the project is of course getting a location to mount the station as well as an Internet connection to upload the data to a server. Speaking with Don, he volunteered his Internet connection to allow data to uploaded. To make this as straight-forward and to require as little interaction as possible, a stand-along system which doesn't rely on Don's computer is going to be ideal.

Next, was how to measure snow depth.

I found two commercially available Snow Depth Sensors. The first I found was the NovaLynx unit. At the time I checked, it has a retail of $745.00. More research also found this sensor by Judd Communications. It's listed on their web site at $652.00.
I'm not sure if that includes a data-logger or not. But it's still pricey for a 'hobby-type' snow depth sensor.

In researching "home-brew", cost-effective options I first found this project put together by Steinar Midtskogen. It uses a sensor called Mini-AE. His project did inspire me to do additional research and really got me excited about the potential for putting my own sensor together.  Update: I have been in contact with Steinar.  He was so nice to learn from since he has already done this.  I learned that he put his Mini-AE in constant ping mode at 10Khz.  That means that about 1 time a second you hear a 10Khz click as the sensor ranges and reports back the voltage. Steinar's install is in a remote area and he's not concerned about bothering anyone.  For my installation behind Don's house, I need to keep the sensor as quiet and discrete as possible.  There's a way to put the Mini-AE into external trigger mode.  More on that later.

The next well documented and intriguing sensor lead me to this project by Chris Nafis. It uses a "Rabbit" processor-based board, That processor looked very interesting to me and was the direction I was planning on heading. I would require the use of some C programming. No biggie. The author of the web site has the source code listed too. I was excited until I found that the company that supplies the processor kit which includes the board for the Ethernet connection, was only sold in lots of 50. That's about 48 or 49 too many for me.

I started some new research on new options which lead me to this other project which discussed one-wire communications. This put me onto a whole new level of research into 1-wire weather stations.

The author of the Weather Toys book uses a processor and board called TINI, initially produced by Dallas (Maxium). I liked the idea of using this processor because this chipset was designed with the 1-wire interface onboard. It's also designed to use embedded Java.

Next I learned that Tim, the author of Weather Toys, experimented with a board called the TStik. This is manufactured by a company called Systronix. The author mentioned that the TStik seems to have a more rugged design which has faired very well in harsh weather reporting conditions.

As is turns out, Systronix is based right here in Salt Lake City, Utah. That's very convenient for me. I started speaking with Bruce over at Systronix and he said that he would provide some support to me in this endeavor. They are also dealers for the MaxBotix ultrasonic sensor which has a serial interface, and will we able to use the serial port on the TStik board. This is now an all-in-one solution for a very scalable, pseudo professional one-wire weather station, that can also do the ultrasonic snow-depth sensing.

Some initial testing with the sensor hooked directly up to a PC's serial port, revealed an aspect to the sensor which I overlooked when I decided to use it. While the MaxBotix sensors are very accurate and provide very stable results. They only have a resolution of 1" or 2.5cm. That's not great, but probably acceptable for this particular application.

Update 9/03/07
I've been told that I REALLY need to mount the TINI processor in the house and run the 1-wire network out to the weather station.  To use the MaxBotix serial sensor would require a VERY long serial cable.  That's not going to work.  Also, the 1" resolution is a bit of a downside.  I wound up purchasing the Mini-AE that Steinar used in his 1-wire prototype station. The next concern was controlling the sensor and using an external 1-wire trigger.  Steinar suggested using a very cool method by which you would use a 1-wire board with 1-wire network activity LED.  By tapping into the LED, you could use the 5v signal from the LED to trigger the Mini-AE.  Unfortunately the board with the LED doesn't seem to exist any more.

I talked to Eric at Hobby-Boards.com he didn't have an immediate solution.  Posting my dilemma on a forum gave me a pretty cool result.  Someone suggest that I use Eric's HVAC monitor board.  It uses the Dallas/Maxim DS2450 chip and can be configured to use one of the 4 channels as an output.  One of the other channels will do the 5v A->D conversion from the Mini-AE.  Excellent. Eric volunteered to modify his HVAC monitor board to allow channel A to provide the trigger signal.

Update 9/25/07
I'm a bit disappointed with progress.  I hooked up the Mini-AE to my multi-meter and has some great success pinging and getting readings back.  It's great.  Next I put the Mini-AE in trigger mode and decided I would check to see how well the 5v trigger worked.  No amount of coaxing would get the Mini-AE to trigger using a 5v signal.

I emailed SensComp to find out what the problem was and this is what I learned...

"In order for the external trigger to operate, you need to take the external trigger enable (pin 4) low or to ground. Then apply an external clock (TTL level square wave) from 1 HZ 50HZ to the external trigger (pin 3). "

So much for a simple 1-board solution.  Now I think I need to commission someone to make a board that will send a 1-50Hz TTL level square wave signal that can be signaled by a modified 5v HVAC board.

Update 11/19/07
Woo hoo! Success. I spoke with Eric at Hobby Boards and he said that the DS2450 output should be 5v TTL compatible. With that information I worked on some code and managed to get a snippet of Java code to control Eric's modified HVAC board.

By creating a loop I was able to successfully cycle the ultrasonic sensor on and off. I chose channel C on the board to receive the voltage returned from the Mini-AE and all works well.

I need to get my code integrated into Tim Bitson's TWS (TINI Weather Server) code. Once that's done, it's just a matter of putting all the parts together and onto a weather station pole. Pictures soon to come!