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CC2650: Ultra low-power sensor mesh network

roman ivnitzki
Prodigy 40 points
Part Number: CC2650
Other Parts Discussed in Thread: CC2630, CC2530, CC2538, Z-STACK

Hi all,

I'm an experienced embedded developer with plenty of 8/32 bit MCUs and many kinds of communication modules. I have been asked to do some research on possible solutions for the following system description:

1. The system will include 20-100 standalone microwave radar sensors for human movement detection. Standalone meaning that each sensor will be battery powered and have an MCU and a transciever. Each mA matters .

2. The sensors need to be sampled at minimum of 3/4Hz, preferably constantly sampling. Upon detection of trigger event (voltage level drop), the mcu should transmit its' ID to central node/modem  for further processing.

3. The sensors will be spread in large outdoor areas with maximum of 30 meters between closest units.  The placement procedure is to be as simple as possible (just turning a switch on or something like that),  avoiding the use of repeaters and such. Think of it as a sensors mine field.

A few questions:

1. From the information I gathered so far I think that the CC2650/30 is the best suit for this purpose. Is that a correct assumption?

2. Using the Zigbee protocol with the mesh networking setup sounds like exactly what I need, as the distances between nodes and the data rate is very low.

3. I am not familiar with the depths of the Zigbee protocol and have no experience with the CC2xxx family. I have seen that there are different versions of ZStack and different supports for the mesh networking on the CC2xxx. Im also not familiar with the terms used for Zstack/Zigbee (ZAP/ZAR/ZC/ZP  etc.).

4. Can you please point me in the direction of the correct layout, version and documantation sources for the rigth MCU/ZStack and any other recommendations you have

Thank you very much in advance,

Roman Ivnitzki

  • 0
    TI__Expert 8950 points
    Hi Roman,

    I will start by clarifying some things about ZigBee mesh networking. There are three types of nodes in a ZigBee network: A Coordinator (ZC), Routers (ZR), and End Devices (ZED). ZC and ZR are non-battery powered devices. Every regular ZigBee network is formed and managed by a ZC, and ZRs can be used to route packets from a one device to another. ZEDs are generally sleepy (i.e. RX off unless polling), battery-powered devices, so this is configuration is what you'd want to use for your sensor nodes. Note that ZEDs do not route packets from other device, and they must be the direct child of a single parent node (ZC or ZR). There are various ways you can lay out your network, but my suggestion would be to have 1 ZC, a few strategically placed ZRs if possible, and then your 20-100 ZED nodes. This way, you do not have (potentially) 100 ZEDs connected to a single parent (ZC), but rather maybe 20 ZEDs connected to each parent, which takes better advantage of the mesh network topology and lessens the load on a single parent device.

    There are also 2 modes that our stack can run in on our devices: SoC mode, which means our chip runs the full application and ZigBee stack, or ZNP mode, where our chip acts only as the network processor (ZNP), and then communicates with another device that acts as the application processor (ZAP) via some interface, e.g. UART.

    For your questions:

    1. The CC2630/50 can only support the ZED configuration in SoC mode, this is due to flash constraints on this device. For your end device nodes this device would be fine. For ZC and ZR devices, you can either use the CC2650 in ZNP mode with separate application processor, or you can use one of our other chips that support ZigBee, the CC2538 or CC2530. Both of these devices can act as a ZC or ZR in SoC mode, and since these nodes are not battery powered the ultra low power mode is not important.

    All of these devices are supported by Z-Stack Home 1.2.2a, available here:
    www.ti.com/.../z-stack-archive

    Our newest Z-Stack 3.0 release only supports the CC2530/CC2538 platforms due to the CC2650 flash constraints, but it is available here:
    http://www.ti.com/tool/z-stack

    Documentation on our stack, APIs, and sample applications are included with the stack download. For more information on ZigBee, you can refer to the ZigBee PRO specification (download at the bottom):

    www.zigbee.org/.../

    2. ZigBee would be good for this use case, but like I mentioned above, if you want to take advantage of mesh networking you will need to include ZR nodes in your network. With only ZC and ZED nodes, your network will effectively be star topology, since ZEDs cannot communicate with each other without an intermediate parent. That being said, using star network topology is also totally fine if you would rather use that for your network.

    3/4. I addressed some of this above, let me know if you have any other specific questions.
  • 0 in reply to JasonB
    Prodigy 40 points
    Thanks Jason,
    This covers my questions completely.
    Roman