I’m working on a project about cold chain monitoring in food transportation. The project has only two requirements: use very cheap sensor (<= 20$ per unit – this is a very strict requirement) and short range of sensor/receiver (about 50~100 meters in open space). I’m looking for a complete low-cost solution composed by RF temperature sensors and receiver. Moreover, I need to interface each receiver to a single board computer (SBC) via RS232 interface, in order to log data and send analysis to a data center through GPRS communication.
Do you think that I have to build a custom solution (maybe using zigbee?!?) or there are ready to use solution available on the market?
This task would lend itself to ZigBee perfectly. Cost is not down to $20 per unit yet unless you were doing the manufacturing in very large quantities. Hardware is almost out of the box ready but the host software would need to be custom.
Check the XBee kits from Digi International (they also do have system integrators to do the custom software available) for some information on what is being done with ZigBee.
Have you checked out the Thermochron from Dallas/Maxim? It handles the temperature monitoring and logging. Even if it isn’t suitable for your project, it is a great device; reset the mission and drop into your area you want to monitor. The temperature is logged and can be reported back at any time.
Since you don’t need the greatest distances, you can use cheap wireless modules if you’re willing to take the time to write code for them. Or if you’re using arduino devices, there are libraries already written that work with these modules.
On top of those, you’ll still need a microcontroller to interface the temp sensor to the wireless, but you could use atmegaXX8’s or attiny’s for a little less cost.
You can find places with bulk discounts on all these items if need be.
The MSP430 RF2500 kit from TI might do what you want. It has temp. sensor built in. Very low power consumption. The kit comes with an AP which reads signal from other nodes, an end device and a demo app. You can buy extra end device for $20 a piece. The AP can talk to either your PC (demo app) via the USB programming dongle, or can hook to any UART device (3.3v).
It could form a small network of one AP and many nodes as well.
TI also has an ez430-RF2480 zigbee design. Too bad they dont’ sell target boards seperately. But you can get 3 target boards and the USB programmer for $99. The MSP430 processor on the target board has a built in temp sensor.
lyndon:
Yeah, nice thing about ZigBee is that it’s much cheaper than Bluetooth. I should switch over
stevech:
lyndon:
$20/unit in what quantities?
check prices at Mouser/Digikey or Digi direct.
$20 is about Qty 1.
I preach: ZigBee is one of many routing protocols used with the 802.15.4 modules. Most applications don’t use anything more than 802.15.4 itself, sans ZigBee.
ZigBee is not a synonym for 802.15.4 and vice-versa, any more than Ethernet is a synonym for TCP/IP
Just “easier” to think of it that way. As long I can treat each module as a serial I/O device I’ll be happy.
stevech:
lyndon:
Yeah, nice thing about ZigBee is that it’s much cheaper than Bluetooth. I should switch over
stevech:
check prices at Mouser/Digikey or Digi direct.
$20 is about Qty 1.
I preach: ZigBee is one of many routing protocols used with the 802.15.4 modules. Most applications don’t use anything more than 802.15.4 itself, sans ZigBee.
ZigBee is not a synonym for 802.15.4 and vice-versa, any more than Ethernet is a synonym for TCP/IP
There are products along these lines that are sold in the RFID space: RFID tags with attached sensors. Some can only take a reading when energized by the reader; some include a battery and will log temperature/vibration/etc to be downloaded later by a reader. I don’t know any company names offhand but I have heard people talk about them.
wiml:
There are products along these lines that are sold in the RFID space: RFID tags with attached sensors. Some can only take a reading when energized by the reader; some include a battery and will log temperature/vibration/etc to be downloaded later by a reader. I don’t know any company names offhand but I have heard people talk about them.
virtually all RFID tags are short-range, meaning from an inch to a foot. So they are in a different application space.
would an 802.15.4 module, battery powered, long range, stuck on a sensor (Digi has analog and digital inputs, no microprocessor needed) - be called an RFID tag?
The industry is calling these “WSNs”, or wireless sensor networks.
