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I have a data logger board with a SIM808 on it. It has Bluetooth 3.0 capability by the SIM808. The board itself implements a battery management system, capable of performing weight, humidity and temperature measurements and also can detect device displacements. All collected data is transferred by GPRS connection to a remote server.

The device itself can be installed into beehives, but it would not be cost effective to have a SIM card for hundreds of hives. So this will only act as a master, that have data logging capabilities as well beside the GPRS capability.

Thus, I am planning to implement slave boards without the SIM808 modules. So instead of the SIM808, a simple wireless communication unit is needed to enable local, wireless communication between the hives.

The master would query all the slaves for their data, and then it would transfer everything via GPRS.

It should look like this, only with a hundred hives:

enter image description here

Now the possibilities for local wireless communication:

  1. Bluetooth, as I said the master device already have Bluetooth 3.0. But I am not entirely sure that Bluetooth is the right way to query a hundred slave for 1 kBs of data.
  2. The master device has an I2C bus, so I can connect I2C compatible ZigBee or other RF module which could be added to the slave boards as well.

Collectable data from slaves won't exceed 1 kB/query.

So all in all can I stay at Bluetooth or should I add ZigBee for example to my devices or are there any other options?

Some more details:

  • range is max 30 meters
  • also as the devices are battery powered, a solution with low power consumption would be good
  • the master would run a query in every 15 mins

The main goal is to make the master able to query the slaves efficiently, and this should be done without modifying the PCB of the master. The two possibilities are Bluetooth 3.0, which is already available for the master, or other technologies that I can connect to the master board via the I2C bus of the on-board MCU. (I do not insist on using Bluetooth, it was the starting point because I already had a BT 3.0 by the SIM808.)

enter image description here

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    I have a distant thought that bluetooth can only support 16 slaves at once. Other than that, seems OK (and a good real-world IoT design problem). Have you considered range?
    – Sean Houlihane
    Jan 17, 2017 at 16:33
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    Seems the limit is 7, but its not a blocking issue. superuser.com/questions/332767/…
    – Sean Houlihane
    Jan 17, 2017 at 16:44
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    Range (and the future-proofing of the range) would be my primary concern with Bluetooth. If you decide to move things around in the future, or deploy more hives, you could find yourself running into trouble fairly quickly. If I were building this I think I'd opt for an el-cheapo Android phone as the hub and an ESP8266 at each hive. That'd shift all your local comms to WiFi, and provide you with highly replaceable parts should you ever need to upgrade.
    – goobering
    Jan 17, 2017 at 16:44
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    Bluetooth seems like a poor solution in this case - the problem just screams mesh network to me (ZigBee would probably work well). If the range required is 30m, you might be looking at some serious power usage (see the table here). At 100mW usage, you'd be looking at mere hours or days of battery life, I suspect, depending on the frequency of transmission. What sort of batteries are you thinking of exactly?
    – Aurora0001
    Jan 17, 2017 at 17:17
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    BTLE would probably be a better fit than classic BT for nodes that need to be battery powered in the long term, but 30 meters will be a stretch for reliability with either. Depending on how much data you need to send, you could consider LoRa, possibly with a Thing Network style gateway, either your own or if there already is one in range.
    – Chris Stratton
    Jan 17, 2017 at 18:15

3 Answers 3

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+50

Alternatively it might be worth to consider wireless Hart (Highway Addressable Remote Transducer). This is a 2.4GHz ( license free frequency band) Smart mesh networking technology that uses 802.15.4 standard. WHart use direct-sequence spread spectrum technology and needs at minimum three main components. Namely wireless devices, gateway and network manager.

Wireless hart network

Click on image for a larger version of the image.

Additionally depending on the network, security manager, adapters, and handheld terminals can be added.

Dust network offers a SOC option and some of them have I2C interface. Attach below is a links to some of the datasheet. Unfortunately my knowledge on this technology is pretty limited thus warrant further research.

References

  1. LTP5901-IPM/LTP5902-IPM
  2. WirelessHART - How it works
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From the perspective of power usage, Bluetooth 3.0 does not seem like a viable choice, given your constraints.

Let us assume that you want to transmit data for 2 seconds every minute, and then sleep for the rest of the time. Given your range requirements of 30 metres, you will likely need to use a Class 1 Bluetooth Radio:

Class 1, primarily for industrial use cases, [have a range of up to] 100 metres (300 ft). Bluetooth Marketing qualifies that Class 1 range is in most cases 20–30 metres (66–98 ft)

I would imagine the lower range would occur in situations where there was not a clear path for the radio transmissions, and perhaps in challenging radio environments. Outside, I would imagine this is less of a problem.

So, assuming the above is true: you will be transmitting for 1/30th of an hour, at approximately 100mW during the transmission phase.

Hence, per hour, you will consume approximately 0.00333 Wh of energy. For comparison, a 'long-life' alkaline AA battery stores around 2.6 Wh of energy. Therefore, your battery would last about 30 days with Bluetooth 3.0, which isn't really bad, but could be a lot better.

These calculations are all very rough, but they should be in the ballpark if the assumptions are correct. EE Times suggests that 5% of the time transmitting is on the high end, and my estimate of 2 seconds / minute is roughly 3.33%.

Bluetooth Low Energy (BLE) might be more viable; this page suggests 10mW power for a 77m range, which would give a battery life closer to 1 year (325 days, more precisely!). However, this would require new hardware, which is, admittedly, a disadvantage.

As I mentioned in a comment, this sort of setup seems perfect for a mesh network, and that should reduce your range requirements significantly, since you won't have to transmit 30 metres to the hub, just 2 or 3 metres to the next beehive. In that case, you could probably get away with a much less powerful radio, which would save battery life.

It may be worth considering one of the mesh protocols such as ZigBee or the new BLE Mesh protocol, which would both suit your use-case well.

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    As per your comment above, as soon as I read the description it was obvious that a mesh network was the answer. Although the OP asked about BT, and the answers are BT related, it may be that he doesn't know about mesh networks. I think that we should explain more and push him in that direction. This would also be informative for future readers. @Bence, start reading at en.wikipedia.org/wiki/Mesh_networking
    – Mawg says reinstate Monica
    Jan 18, 2017 at 8:12
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    @Mawg I don't use but SIM808 offers BT 3.0, that's why I asked about BT first. I know a little about mesh networks (ZigBee initially mentioned in the question), but if Bluetooth could have solved the problem I would not have invested into another module. But it seems that BT 3.0 is not the way for it. So I would welcome a detailed answer about mesh networks or ZigBee especially.
    – Bence Kaulics
    Jan 18, 2017 at 11:11
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    @Mawg I primarily left that bit out because it's not something I can answer particularly well, so I left it out for someone else to address more properly. If you (or someone else) could address the mesh network part more directly, I'd happily upvote that!
    – Aurora0001
    Jan 18, 2017 at 15:05
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I have document some aspect of BLE low power aspects as a response to What is the difference between Bluetooth Low Energy and Bluetooth BR/EDR in Park mode?. Here are is a suggestion.

Looks like a SIM808 has a serial interface. So I suggest integrate the SIM808 module with a Dual Mode Class 1 BLE such as KC-5170. I think you could use a single mode BLE too.

SIM808 Serial Interface

SIM808 Serial Interface

KC5170 Serial Interface

KC5170 Serial Interface

Configure above is a master device, with BLE Class 1 single mode devices as slave devices.

BLE Master Salve Proposal

I suggest using a BLE Class 1 Single module such as the BR-LE4.0-S2A. I believe an unlimited amount of slaves can be connected to the master (needs conformation)

Also below is simplified block diagram of BLE dual and single mode.

BLE 4.0 Configuration

BLE power consumption Graph

BLE Power Consumption Graph

I suggest reading references for additional details.

Update (1/22/2017): Base on the provided information not too sure the available GPIO's, SPI bit banging might be another option to connect to SPI based BLE module. A I2C base big banging tutorial is attached for you reference.

Another option is to use BLE SOC such as TI CC2640, which supports I2C. The compromise is the device is a class 2 device.

CC2640 BLE
Click on image for a larger version of the image.

References

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    This proposed BLE above BT 3.0 (which seems reasonable), but doesn't address the question of would a mesh protocol be better (I guess it is similar, so cost and familiarity could be the deciding factor).
    – Sean Houlihane
    Jan 18, 2017 at 9:26
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    Please clarify on each picture and picture what the source is rather than just adding a list of references on the bottom.
    – Helmar ♦
    Jan 18, 2017 at 10:06
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    The master board is already manufactured. So I can go either with BT 3.0 or something that can be connected via I2C, these are the already mentioned possibilities for me.
    – Bence Kaulics
    Jan 18, 2017 at 10:15
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    @Helmar, I have explained this in greater detail here. Sorry I don't have free time to duplicate effort for an volunteer effort. But the research has been done, and the references linked for the interested. I am sorry, no more free time.
    – Mahendra Gunawardena
    Jan 18, 2017 at 11:42
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    @SeanHoulihane All I have done is shared some of my research mostly in power consumption, to help OP to make a decision. In engineering there are many technical and non-technical factors that play into to making the change. Also I think TI has a module that you can load either Zigbee or BLE stack that is something to consider when building HW.
    – Mahendra Gunawardena
    Jan 18, 2017 at 11:46

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