Weather Node

weather sensor

Weather sensor pod on roof.  The rain collector
(funnel) has since moved to

One of the nodes on the home control network is my weather node. The system tracks 8 parameters. They are : wind speed, wind direction, rain fall, outside temp, outside humidity, inside temp, inside humidity, and barometric pressure. I then derive three additional parameters, which are : wind gust (max winds over a period of time), the outside dew point, and the rain fall rate.
weather node
The weather node

The weather node is shown above. It has an LCD display with the name of the parameter shown on the LED display. Currently, the outside temperature is shown. At the top left is the switch to change the parameter shown, the middle top has the inside temp and humidity sensor. On the bottom left (red plug) is the power cord, the middle bottom is the Home Automation Network connection, and the bottom right is the fiber optic connection to the sensor pod on the roof.
The external parameters are collected by an 18 pin PIC inside the weather instrument on the roof. The data is relayed via wire and fiber optic connection (the latter for lightning protection) to my inside node which displays one of the above parameters on a four digit 7-segment display and a 16 character LCD panel. The inside PIC also handles communication to my HCSII conformant network to allow the home control computer access to this data.
If you wish to build part of the system, here is how I would suggest you go about it:

Anemometer and Wind Vane

The design of both these items is from the Electronics Now, Oct. 93 article by Fascinating Electronics (FE). They are made from commonly available items such as Schedule 40 PVC tubing. I purchased some hard to find parts from FE, but 90% of the items were bought at my local home center (Lowe's). I made two small changes to the anemometer, I used a Hall effect sensor instead of the magnetic switch, and I used a 1/4" bolt instead of the #8 bolt as the main axle. I also used 1.25" pipe instead of the 1.5" pipe throughout, and added a lightning arrestor to the top of the whole thing. I estimate the output of the anemometer to be approximately 0.476 revs/sec per mile an hour of wind. The friction is low enough that it start rotating at 1-2 mph.

Rain fall gauge

The design is similar to the EN article, except I adapted the whole thing to fit inside a 1.25" 'T'. This makes it much more compact, and allows it to be fastened by suitable plumbing to the above two instruments on the roof stalk. It has a resolution of 1/32" of rainfall, which is a little less sensitive than original sensor since I used a more compact funnel--I was afraid of saturations in heavy rain, and for cosmetic reasons.

Microprocessor in the weather pod

The microprocessor inside the weather pod. The silver RJ11 cable
on the left leads to the optical link and power supply,
the ribbon cable on the right leads to the transducers.

Temp sensor

I decide using the plain old LM34 as the temp sensor. This outputs 10mV / F, and by setting the reference input on the A/D on my PIC to 2.55 Volts, it allows me to directly read degrees F with no analog processing circuitry. I purchased the sensor from Digi-Key. By biasing the LM34 appropriately, I can read temps down to -25F.

Humidity sensor

This is the moisture sensitive capacitor that detects humidity. I purchased this from Newark Electronics for about $9. The circuit I use is the same as in the EN article. My PIC counts the frequency directly, and results in good accuracy since my only temperature sensitive components is the humidity sensor and two 100ppm/C resistors (the chip oscillator has a very low temp sensitivity). Vishay Corp. part #2322-691-90001, Newark part #89F5822.  [A check in Jan 2016 shows that this unit is discontinued.  An alternate source is Digi-key part no BC1333-ND (courtesy Steve Lapinskas)]

Microprocessor in the weather pod

The micro installed into the tube of the weather sensor pod.
The result is a neat installation that is easily removable.

Barometric Pressure

This sensor is one of the Motorola absolute pressure sensors, also purchased from Newark. It comes with a small port so you can attach some tubing to it. With a gain of about 5 or 6 on the output, you can get 10mV/0.01" mercury. This should be plenty for weather prediction/ logging applications. The sensor is Motorola #MPX5100ASX and costs about $27.00. The sensor itself is made of a semiconductor, and has temp compensation and and instrumentation amp built right onto the same die.

Fiber connection

The kit is sold by Digi-Key as an experimenter's kit. It includes fiber, one transmitter, and one receiver in the SMA style of fiber optic holder. Operation is rather simple. You forward bias the LED, and the optical transistor on the other end conducts. By suitable biasing one can use this to replace an EIA/RS232 line. Since air breaks down at about 3 megavolt/meter, this will afford me some protection against lightning.


If you would like to build your own, I would suggest that you lookup the above mentioned article. It also contains the address of Fascinating Electronics, from whom you can buy the hard-to-find parts such as the bearings and the dual wiper pot for the wind vane.

In addition I would like to add that I appreciate all the posts and email that I received from my request for discussion. I think the most important 'lesson' from all of it is to take lightning seriously.
Now the fun part of collecting and analyzing data begins. I have already noticed a few well known correlations among the various data points: - at night the temp falls, the reverse is true during the day (surprise!). - with no rainfall or strong wind, the falling temp at night is accompanied by rising humidity. - rapid changes in barometric pressure is accompanied by strong winds.
The local NBC affiliate used to offer 24 hour history plots of the parameters that I am measuring. When comparing the data, one is struck by the similarity in their appearance.

Humidity at WRC4
Humidity chart at WRC4 for 3/26

Humidity at my house
Humidity chart from my weather station for 3/26

Related Links

  • Weather Updates in text
  • Fascinating Electronics
  • Long term update

    • March 1999. The anemometer stopped working. I was able to easily take the sensor pod down from the roof to find out why (thanks to the access window mentioned above). It turns out that the ball bearing that I used for the anemometer was damaged (after 3 years of operation) and needed to be replaced.  This episode made me realize that I needed a spare ball bearing, and I was pleased to find out that Fascinating Electronics (FE) was still operating, and they are now web accessible. Since 1996, they have upgraded various parts of the weather sensor. In particular, the anemometer cups are deep drawn aluminum, and the wind vane is also aluminum. This new ensemble looks very nice, and I will probably upgrade parts of my system in the future. I ordered two wind vane wiper pots and two ball bearings.

    New modified weather station pod.  Lightning arrestor and rain gauge removed.

    • October 30 2006.  Roof pod stopped working.
    weather slave node
    Image of the sensor electronics taken in 2020.  After almost 25 years on the roof
    everything is quite corroded.

    • June 2020.  Total redesign of the roof sensor unit. After almost a quarter century in the elements, the electronics inside the roof sensor unit (so-called Weather Slave) have corroded and stopped working.
      • I built a new electronics unit and moved its location into the attic so that it is less prone to corrosion.  It can be operated either in the attic or sitting at the Weather Node for easy code development (using no additional wiring).  Instead of using UV erasable device (PIC 16C71), it uses a Flash based 16F877.  Much easier code development and In-Circuit Debugging is very handy.  See image below
      • Removed the wind vane and I decided to focus on digital only interfaces.  Thus I eliminated the outdoor humidity (sensor would fail after a few years due to temperature swings), and also the wind vane (the dual potentiometers would fail due to the constant wiping back-and-forth).  Also eliminated the roof temperature as it was of limited value.
      • The only sensor remaining on the roof sensor is the anemometer, and it connects to the Weather Slave via a three-wire cable to drive the hall effect sensor in the cap of the spinning sensor.  It is now also much lighter and safer to handle for me than the original design.
      • This weather slave now has its own 1-Wire network and collects temperature data for the attic zone, and the heat pump air handler unit.  Initially this function was handled by the Thermostat Node, but I found that running such a long 1-Wire network proved unreliable (too much capacitance on the line).  So I greatly reduced the length of the network for the Thermostat Node and the temperatures for the Heat Pump are now monitored by the Weather Slave.  These temperatures are the Intake, Exhaust and Attic Temperatures.
    New weather slave electronics
    New version of the weather slave node electronics.

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