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Help: project related to wireless weather station

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pallepop

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project related to wireless

Can somebody help me to do a project related to wireless weather station.
The requirements are simply described as follows.

Function:
Wireless remote measurement system that communicates at 433MHz.
The purpose of the system is to measure Temperature, Relative humidity, sound.
The range is 50 to 100 meters. 1 or 6 units per base station.

Communication:
Use RF module to transmit and receive data.
Something like Nordic Semiconductor RF Chip nRF9E5, or nRF24L01 and pic18FXXX.

Power Supply:
Something that’s pretty small – about the size of a 9V battery

Data output:
LCD display to show the information of the weather

So i would like to obtain some advise from you all. ...would be welcomed.

Thanks for the help from you guys.
 

akilpatrick

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wireless weather station revers engineered

I've done a bit of digital sending over small RF modules. First you need to decide if you want/need bi-directional communication or not. You might find it cheaper and easier not you. Each sensor could sleep for a while, and then wake up every so often (depends on how fast you need it) and take a measurement and then transmit it to the receiving station.

By implementing a bit of randomness to the time each unit sleeps, you won't get collisions very often. This would be much simpler than having a bi-directional system and requiring a transceiver at each node.

In terms of data transmission, use something like bi-phase mark or manchester coding. This means that the data is always changing, and you won't be sending long strings of 1s or 0s. This can improve clock recovery of the signal, and is probably suggested by your RF modules as the preferred method of sending data. You can write a quite simple receiving routine in software. Keep the speed low to improve the signal quality.

Also, make sure you use a checksum or CRC to ensure that the received data is valid. CRC-8 or CRC-16 is better than a simple 8 bit checksum. You WILL get data errors in reception, so it's best to make sure that you ignore data that's wrong, instead of displaying some ridiculous values on your system.
 

alexz

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weather station rf protocol

Why RF and not ZigBee?
 

pallepop

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all projeccts about weather station

Hi,
Thanks for your response.
But can u help me to make a block digram ?
 

akilpatrick

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weather station microcontroller project

ZigBee is RF. And these days might indeed be a good system to try since there are some quite inexpensive RF modules that implement the ZigBee protocol and make it easy for users to send and receive data without handling the low-level signalling.

However the original post mentioned that the system needed to work on 433MHz, which is not a ZigBee band. (I assume that he has certain RF modules in mind) To quote Wikipedia: "ZigBee operates in the industrial, scientific and medical (ISM) radio bands; 868 MHz in Europe, 915 MHz in the USA and Australia, and 2.4 GHz in most jurisdictions worldwide."

If the frequency of operation is open for discussion, perhaps check out some ZigBee stuff. Digikey sells some modules that are in the $20-40 range and have good docs. (I've looked at them for an application)

In terms of a block diagram.... it might look something like this:

SENSOR -> MICRO A (PIC?) -> RF TRANSMITTER

....air.....

RECEIVER -> MICRO B (PIC?) -> DISPLAY DEVICE, or RS-232 or USB to a computer


MICRO A would get sensor data from A/D or other means (I2C) and generate packets to send to the receiver. MICRO B receives data, figures out what it is, and then displays it on an LCD, sends it over RS-232 or USB or whatever. Not much changes if you use ZigBee modules, except that you automatically get bi-directional communication.

But as I stated previously, you might not need/want bi-directional communication. With a somewhat random sleep interval, you could probably save a ton of battery life by letting the modules go to sleep for most of the time and waking up every so often to send a reading back to the receiver. By slightly randomizing the sleep time you can avoid too many collisions when multiple sensor try to transmit at the same time. If you had a bi-directional system where MICRO B polls for readings, the radio in every receiver would have to be on all the time listening for commands.

Since you're using RF, I can only assume that these remote sensors probably don't have a hard-wired power source. This is why I suggest the sleep mode and power savings.
 

pallepop

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wireless weather monitoring project

How can the receiver save the power in sleed mode if yes. how can u synchronization the signal.
 

akilpatrick

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circuit to low power wireless weather station

The topology I mentioned would involve the receiver to be active all the time. I'm imagining a system which would consist of a receiver/display device (or PC) located inside somewhere, connected to mains power so that it's active all the time. The remote sensors would be located outside with their various sensors (temperature, humidity, wind, etc.) and would run on batteries.

In this type of system, the receiver need not be low power to the point of being able to run off batteries for long periods. Only the sensor/transmitters would need to be low power. By using a PIC or similar microcontroller with a very low power sleep mode, and controlling power to your transmitter, sensor, etc. through software, you could make the unit run for months or years on a battery. This is an interesting and very worthwhile design exercise. I suggest you read the following app note. I can't find a link to it on Microchip's website, so I've posted my copy here.


Andrew
 

pallepop

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circuit wireless weather station

Thanks for your response.
But wireless weather station receiver do not have a PC or connected to mains power only 9V battery how ?.
 

akilpatrick

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bi-directional interms of zigbee

Well, that's an interesting question.... I've never reverse engineered one so I don't know.

Perhaps the receiver circuit is low enough power that it can stay on all the time.

Do some calculations based on the info in that app note I posted and find out. :)
 

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