SparkFun Forums

[marckam]

Hello all,
I need to have following monitoring system, and I would like to hear your opinions what is the cheapest way to do it, what is the cost for parts approximately and how much would it cost if someone builds it for me?

- 10 battery powered wireless temp&humidity sensors, battery life time 1 year. Each sensor can be powered by 2-4 AA or AAA batteries.
- One receiver. It has to tell the status of each sensor by led indicators. Green led if temp&humidity is within the specified limits, and red led if it´s out of the limits. Status update rate 1Hz. Receiver can be powered by 12v power supply.
- Max distance between transmitter and receiver up to 35 meters

I really appreciate if you can give me your comments!

Thanks in advance,
Mark

[waltr]

Not the cheapest but the easiest is to use XBEE series 1 modules and an Arduino at the "Reciever" end to get the data from each node and run the display LEDs.
1Hz update rate and 35 meters is quite reasonable for this setup.

[Valen]

I'd say get a bunch of commercial weather station sensor modules. One year battery life might be stretching it though. Depends on the battery (chemistry) and outside temp and humidity. Hack the receiver of the base station to an arduino that lights the leds. Materials probably doesn't get any cheaper than that. The most cost would be found in investing time to reverse-engineer the wireless protocol of how the temperature and humidity is embedded. And use that knowledge to write the basestation code in the Arduino. With luck someone else has already hacked the wireless protocol and published his finding on the internet.

[EDIT] The ones I found in a local discount store (because most were defective and not complete) for myself only reported temperature in around 45 second intervals. I doubt the temperature changes that quickly outside anyway. So, I'm curious why you need 1 Hz update rate. But the modules are not transmitting synchronous, so I guess that would only apply to the basestation updates giving last received statuses.

[marckam]

Thanks for the replies!
Zigbee could be the best solution, but I´m afraid it´s going to be too expensive when looking at the cost of xbee modules...
Weather station would be good idea too, I have to look if I can find one with ten sensors and higher update rate. 1Hz is about what I need, because it has to tell fast enough when something is wrong...

What do you think, could this be made using cheap RF 433 transmitters and receiver?

I appreciate your comments!

[waltr]

Yes it could be done with cheap 433MHz tx/rx but these will require a processor on each TX to encode the data for reliable transmission. These cheap TX/RX use OOK modulation which needs at least Manchester encoding.
Not hard to do since many people have done this and there are plenty of examples on the web with code. look up "virtual Wire".

[marckam]

Thanks Waltr, that´s exactly what I wanted to hear. I have to start studying this. I´m glad about any tips you can give about component choices etc.

Markus

[waltr]

I'll suggest getting one of the Arduno boards then start learning how to program it. Start with learning how to blink an LED.
You will need to use its Analog input and the ADC to digitize the temperature sensor, if the one you use outputs an analog Voltage. Or learn how to do I2C or SPI if the temperature sensor uses one of these serial busses.
Then learn to interface to the RF TX and RX to send and receive the data.

Last is transfer and you learned onto a smaller Arduino boards and write code for the Receiver side to gather all the data and run the status lights.