Let Us Work Together For a Weather Station

[theo92]

Can you help me to design a home weather station.......my childhood dream is going to be true at tennage.....

I know basic PIC programming in C..learnt from gooligum elec....

My plan is to add 2/3 temp sensors..MCP9700A from microchip 10mV/deg C and
One pressure sensor MPX5999D from freescale....

And I want to output these values to a 16*2 LCD....and to store the data in a EEPROM or a SD card? which should be easy to program? SD card or EEPROM?

This device will record the current temperature and pressure with a interval of 1 hour......so in 1 day it'll record 24 sets data.

A 24LC512 512KB EEPROM should be sufficient to hold data of one week that is 168 sets of data.

Now I want to use PIC18F2550 for the application...
using it's AN0, AN1,AN2 analogue inputs for temperature sensor and AN3 for the pressure sensor......can I use that? and RB0-7 for the LCD and some other port for the EEPROM...

now, which freescale pressure sensor to use........i have the options to use

**broken link removed**

**broken link removed**
**broken link removed**

this is my favourite sensor..... it can maximum detect 1000kPa..where normal atmosphere pressure in 100kPa....i'm using that because first i wanna sample with freescale then to buy two or three....

now, i only have some experience in very basic PIC programming in C.no xp in ADC programming.......so, is here any guys who will work together with me to write the code and to help me in the circuit design?i think someone will....this is not a commercial project ...i'm a school student and this project is for my intense disire for such a thing and for our city educational science exhibition......i wanna show 'em something new. the guys here don't even know what PIC is...

so please.....anybody? I'll gladly accept any help any suggestion or comments from anyone.....

Let Us Work Together For a Weather Station

 

[Leftyretro]

First your going to have to learn more about pressure sensors. Don't worry, it's not difficult to understand and can be quite educational.

The sensor you have selected is in fact a differential pressure sensor. That means it measures the relative difference between it's two pressure ports (P1 & P2). Some of these sensors only give you physical access to one port but the second port is still there internally and is sensing the ambient pressure. Because the sensor can only respond to a differential pressure between it's two ports, it will never be able to sense a change in barometric pressure changes. As barometric pressure changes both ports will sense the same amount of pressure and therefore have a net zero differential pressure between them and a measurement "zero output".

What you need is called an absolute pressure sensor. While internally it still has two pressure ports, one port has had a vacuum pulled on it and then sealed tight. Therefore the second port will always be sensing the pressure difference between it's port and the fixed 'reference' pressure and is suitable to measure barometric pressure changes (as well as vacuum pressure values)if sensitive enough.

Another area to understand with these kind of pressure sensors is that they come in generally two styles. First kind is what you might call a raw sensor. It is basically just a resistive Wheatstone bridge circuit where you supply a fixed driving voltage or current and you measure the voltage differential across the bridge (usually in millivolt range) to sense the pressure differential. The second kind of sensor has more electronics integrated in the sensor and amplifies the voltage to a more useful range and often has temperature compensation built in to make for a more reliable and accurate sensor. Of course the second kind costs a little more but can help make for a more successful result. The sensor you linked to is an example of a sensor that has built in amplification and compensation.

So to recap you need to understand and specify the type of pressure element you need, differential or absolute. Then you need to determine the range of pressure measurement the sensor is designed to measure. And finally you need to determine if you want a raw sensor or one with built in amplification and compensation.

I've built several barometric pressure gages over the years and had a lot of fun learning about that field. Did you know that a well calibrated and sensitive barometric pressure can be used to measure elevation?

Good luck

Lefty

PS, You don't need to be a weather man to know which way the wind blows........

 

[Gordz]

There are a few of these on the 'net. I reckon if you take the best ideas from all of them you could create a really great station. Maplin once had a project and the way they sensed wind speed and direction was pretty good. They used a code disk and a few IR reflective sensors to read it. One disk was coupled to a wind vane and gave the direction of the wind and another with plastic wind cups on a rotating shaft gave the wind speed.

 

[theo92]

Leftyretro First your going to have to learn more about pressure sensors. Don't worry, it's not difficult to understand and can be quite educational.

The sensor you have selected is in fact a differential pressure sensor. That means it measures the relative difference between it's two pressure ports (P1 & P2). Some of these sensors only give you physical access to one port but the second port is still there internally and is sensing the ambient pressure. Because the sensor can only respond to a differential pressure between it's two ports, it will never be able to sense a change in barometric pressure changes. As barometric pressure changes both ports will sense the same amount of pressure and therefore have a net zero differential pressure between them and a measurement "zero output".

What you need is called an absolute pressure sensor. While internally it still has two pressure ports, one port has had a vacuum pulled on it and then sealed tight. Therefore the second port will always be sensing the pressure difference between it's port and the fixed 'reference' pressure and is suitable to measure barometric pressure changes (as well as vacuum pressure values)if sensitive enough.

Another area to understand with these kind of pressure sensors is that they come in generally two styles. First kind is what you might call a raw sensor. It is basically just a resistive Wheatstone bridge circuit where you supply a fixed driving voltage or current and you measure the voltage differential across the bridge (usually in millivolt range) to sense the pressure differential. The second kind of sensor has more electronics integrated in the sensor and amplifies the voltage to a more useful range and often has temperature compensation built in to make for a more reliable and accurate sensor. Of course the second kind costs a little more but can help make for a more successful result. The sensor you linked to is an example of a sensor that has built in amplification and compensation.

So to recap you need to understand and specify the type of pressure element you need, differential or absolute. Then you need to determine the range of pressure measurement the sensor is designed to measure. And finally you need to determine if you want a raw sensor or one with built in amplification and compensation.

I've built several barometric pressure gages over the years and had a lot of fun learning about that field. Did you know that a well calibrated and sensitive barometric pressure can be used to measure elevation?

Good luck

Lefty

PS, You don't need to be a weather man to know which way the wind blows........

Thanks, friend; I really just ignored the differential and absolute type sensors......now i realised my mistake.....here always P1=P2; hence P1~P2=0....but in case of absolute pressure sensor(ps), P1=0; P2= given pressure...so, P2-P1=P2.....

yeah!!i've to use a absolute pressure sensor..what is gauge type sensor?
what about it:

**broken link removed**

it's a gauge type sensor...and freescale semiconductor listed it in the search result of absolute pressur sensor...i think i can use ya..not that?

will you help me in wriring the code?without that i cant able to make out...anybody

 

[Leftyretro]

"yeah!!i've to use a absolute pressure sensor..what is gauge type sensor?
what about it:

FREESCALE SEMICONDUCTOR|MPX4250GP|IC PRESSURE SENSOR | Farnell IN

it's a gauge type sensor...and freescale semiconductor listed it in the search result of absolute pressur sensor...i think i can use ya..not that? "

Gauge pressure is just the industrial name for a differential type measurement, so it's not what you will need.

From your site listing your going to have to select a sensor from the absolute table I linked to below. Just be sure you select the correct range (sensistivity)needed for normal barometric use. I think a 0-200 kpa range would put normal barametric pressure near in the middle of the sensors range, but do your own research/calculations because understanding the range and what you want to measure is part of the journey to success.

**broken link removed**

Lefty

The pump don't work cause a vandel took the handle

 

[3v0]

A lot of home brew weather stations use Dallas 1 Wire sensors. These sensors are connected in parallel along a twisted pair networkthat can extend for 200m when driven by a uC, up to 500m if a special interface chip is used. You can download C libs for doing Dallas 1 wire.

I have been running a simple weather station using Peter H Anderson's WX175 for about 3 years. I have 5 temperature sensors and pressure. It is a 16F based solution with an RS232 interface. The setup is used to control a small greenhouse but it also logs/graphs the data. See WX175.blogspot.com.

I like the anemometer and vane kits from **broken link removed**. They are $50 each but worth the money as they are very rugged precision units.

A rain gauge is easier to build. The plans for the tip bucket have been posted here (maybe). If you are interested I can find them again.

I would like to put the wind and rain sensors on a pole. Maybe power them with a small wind turbine and/or solar. Use a radio module to transmit the data to the house.

3v0

 

[theo92]

Thanks everybody for there reply....for their valueable and informative speech 'bout that...

Firstly, At first I want to sample the pressure sensor from Freescale.....but absolute pressure sensors are not available as sample.........can anybody see the sample site of freescale for me looking for a absolute pressure sensor

Secondly, Dallas/Maxim 1-wire sensors are the best sensor I ever seen.as they can 'throw' their digital signals via a twisted pair of wires from long away......but the problem of availability and price....the shops take about double-triple price of the Dallas prouducts.

Thirdly, I realised SHT1x or SHT7x sensor is the best kinda sensor ever.......but again it's NA...

So, I've to go for discrete analogue sensors with decoupling caps.are they not accurate ebough?

Now, I'll post the schematic here which was designed by me.using PIC16F877A........will you help me in writing the code?

Is there any tutorial regarding how to read write external EEPROM lie 24Lx512

 

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