More Thoughts From RF Integration Chat: Wakeup Radio

During our RF integration chat session last week, an additional design concept was brought up. Dirceu Rodrigues talked about a radio link used to bring the rest of a complex system out of its sleep state. The link uses a ultra-low-power RF receiver. When it hears the proper signal, it wakes up the rest of the system. Rodrigues used the example of a ZigBee radio.

A radio using the ZigBee protocol or specs is already considered a low-power device (as networks go), but power draw can be reduced further. In fact, some devices are powered from coin cells, other very small battery packs, or super-caps. The latter are typically used in conjunction with energy harvesting systems.

For these applications, you would want miniscule power draw all the time. The technique here is to combine the ultra-low-power receiver (always on) with burst-mode sensors, a microcontroller (MCU), and the ZigBee radio. When the system wakes up, the digital clock source is enabled, and so is the MCU. The sensors monitor their respective aspects, and the MCU processes the sensor information. The ZigBee radio is enabled, joins the network, and sends the data. Then everything goes back to sleep.

If you could combine the wakeup receiver, the ZigBee radio, the MCU, and perhaps a real-time clock, you could make a device that not only uses little power but also takes up little space. Rodrigues suggested that such a device would be suitable for inventory control. It could be attached to each piece of merchandise. You could walk into your warehouse and quickly check stock/inventory levels. Or, in a tool crib, you could quickly locate a particular tool (or see if it's been loaned out).

There is work being done along these lines. A synopsis on the University of Michigan's Association of University Technology Managers indicates that researchers are already working on such a radio design.

While consuming 98 nW of power during transmission and 11 nW while [idle], this wake-up radio has a sensitivity of -41dB at 915 MHz and has a transmission range up to 6 m. It has been developed for on-off keying (OOK) modulation, can transfer data at 100 kbps and has a chip space requirement of 0.03 mm2 .

Have you done design work with such RF devices? Let us know about frequency of operation, data rate, power draw, and range.

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5 comments on “More Thoughts From RF Integration Chat: Wakeup Radio

  1. David Maciel Silva
    July 31, 2013

    My experience with RF systems is applied for data transmission, I used the modules ready telecontrolli,

    The working frequency of these items is 433Mhz, 5V and a current of 7 mA approximately

    the link below for analysis of the data sheet, these modules typically applied to telemetry systems, temperature, and other information obtained by the maximum distance without obstacles was 200mts.

  2. ZekeR0
    August 6, 2013

    “If you could combine the wakeup receiver, the ZigBee radio, the MCU, and perhaps a real-time clock, you could make a device that not only uses little power but also takes up little space.”

    Linear Technology recently acquired a company called Dust Networks which makes products that do just that. The products use duty-cycling to minimize power consumption while forming a mesh network and optimizing packet flow, all through a robust and secure protocol. It's largely aimed at large sensor networks for industrial control and monitoring, and can be powered by energy harvesters or by batteries that last for years. Pretty impressive system.

  3. Brad_Albing
    August 6, 2013

    @ZekeR – Good info – I'll check that out. Great minds think alike, I guess.

  4. RedDerek
    August 6, 2013

    Put the pieces to gether and then add a few of transmitters in the house. Now when you want to know where an object is (that is attached to the device), it could triangulate itself based on the transmitters and then one can walk to it. It then would not matter if you forgot where you placed the remote. I am talking a mini GPS system within the house. Have the house mapped relative to the tranmitters and an application would pinpoint the object you queried.

  5. Brad_Albing
    August 11, 2013

    @RedDerek – It won't be long before this will be done – just a matter of getting ultra low power devices fabricated and then getting them produced in sufficiently large quantities to get the cost down to something reasonable. Maybe in a couple of years we will be there.

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