A Weather Station - Circuit Cellar

A Weather Station

Utilizing the WIZnet iMCUW7100

Embedded Processor

Product: Weather Station For: Design Contest 2010 Sponsors: WIZnet/Circuit Cellar Date: June 30, 2010 By: 003206

ABSTRACT This contest entry brings another dimension at implementing a fully functional Weather Station using embedded microcontroller technology and some very attractive off-the-shelf sensors. My first thought was to make a totally self-contained system that utilized a solar system for power and a wireless connection back to the main router in my home. The bulk of the system would be contained in a waterproof enclosure in the great-outdoors powered by a solar cell with battery and charging system. With this arrangement, the sensors would be very close to the electronics package.

In following the rules of the game, the WIZnet iMCU7100EVB was the tool of choice be used for our designs. The WIZnet Evaluation board houses the iMCU W7100 processor that is a single-chip solution to Internet connectivity. It integrates the 8051 industry standard 8-bit microcontroller, which also contains 64Kbyte of static ram along with a hardwired TCP/IP core that can support a number of protocols and 8 sockets of simultaneous communications. The W7100 also has an additional 32Kbyte of ram to support data transmission. The chip has a built-in UART to provide an RS232 connection to other devices. The evaluation board also has an on-board MAC-Jack (Transformer) and RJ-45 connector to allow direct connection into a LAN. The iMCU7100EVB also came with the Keil ‘C’ Compiler for the duration of the contest. I feel this won’t be long enough to do some really serious work, but it will have to do.

I needed to connect this Evaluation board to the sensors that were needed to gather the weather data. The 8051 had a nice array of GPIO but I needed analog inputs and the possibility of SPI or IIC communication connections along with an input-capture or two. My first choice because of familiarity was to use the Microchip dsPIC30 family of processors. I still had the compiler from the 2007 Microchip/Circuit Cellar contest and it made a good choice with its speed, computational ability for calibration of the sensors and peripheral support. The dsPIC30F3013 was chosen to do the job of the front-end data acquisition for the weather station. Being a working person with a family, I don’t have a lot of time to dedicate to project like these, so I decided to drop the solar-power dream and make this a simple attempt at a weather station which can be housed in-doors so a 4x20 character display was added for direct indication of the weather. The WIZnet evaluation board provided the Internet connectivity so that the weather can be viewed anywhere in the world. So now Warren, Mi will have another amateur weather station home built with some of the best products that the industry has to offer. CONCLUSION The outcome of this project provided a start into building a more advanced weather station. My future goal is to continue to add sensors to the existing platform and let the sun power the system by adding a solar cell, batteries and charging system. If it can be done economically, a wireless internet connection will also be added.

Below is a screen dump of the web-page that the completed system provides.

Below is a photograph of the Weather Station with the display operational.

Bill Of Materials June 30,2010

Item Quantity Reference Part

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1 1 C1 1 0uF

2 5 C2,C3,C4,C9,C13 .1uF

3 2 C5,C6 47pF

4 2 C7,C8 33pF

5 4 C10,C11,C14,C15 1uF

6 1 JP1 PowerInSelect

7 2 JP6,JP7 INV SELECT

8 1 J1 ICD2

9 1 J2 Male: PZC14SACN

10 1 J3 HEADER:5-10261702

11 2 J4,J6 HEADER: 22122084

12 2 J5,J7 HEADER: 22122064

13 1 P3 PLUG:87456-4

14 2 P4,P6 PLUG: 22013087

15 2 P5,P7 PLUG: 22013067

16 1 RP1 10K

17 1 RS232 747905-2

18 1 R1 2K

19 2 R2,R3 100

20 1 R4 820

21 1 SEN1 SHT75

22 1 SEN2 MPXA6115A

23 1 SEN3 LM94022

24 1 SEN4 OH090U

25 1 SEN5 5K

26 1 TB1 253523653

27 1 U1 dsPIC30F3013

28 1 U2 LM340-5

29 1 U3 MAX232D

30 1 Y1 ECS73204X

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Bottom of Weather Station board showing Microchip dsPIC30F and MAX232D. Top of Weather Station board showing connectors.

The Display has been added to the top of the board. Below, the completed unit with both processors and connections to the sensor packs. The unit has been powered up and is undergoing testing.

Above shows the construction of Sensor Pack #1 which contains the SHT-75 and the MPXA6115A. Below shows the display indicating the TM – Temperature, RH – Relative Humidity, BP – Barometric Pressure, WS – Windspeed, WD – Wind direction and DP – Dewpoint Temperature.