The radio communication technology is the heart of the BigClown IoT Kit. This document describes the basic operation of the radio.
With BigClown, you can build your own network in the Sub-GHz band.
The radio frequency 868 MHz (for Europe) or 915 MHz (for the U.S.) allows long distance communication and offers low-power operation. Since this frequency band is used for signal messages, you will not encounter interference with streaming protocols like WiFi, Bluetooth, etc.
We have done several radio communication tests. We claim, that from a single point, you are typically able to provide a full-house radio coverage.
On the other hand, several factors influence the communication distance - the most important is the building material from which you have built your house, obstacles in the path, interference from other appliances, etc.
The only objective radio communication range measurement is a so-called line-of-sightdistance measured outdoor.
On the other hand, if the radio communication range is not sufficient, the network can be expanded on IP level thanks to MQTT message replication to a master server.
BigClown supports only star network topology. Such configuration offers high reliability, easy troubleshooting and deterministic service time from batteries.
There are two types of devices in the BigClown radio network:
You can pair up to 32 devices.
Every node has to be paired to the gateway. A node device can be some sensor (e.g. temperature, humidity, CO2) or actuator (power relay, LCD display, LED strip controller).
Pairing process is very straightforward procedure:
This is done by cycling the power on the node device. On battery-operated node, you simple remove the batteries, wait a few seconds (to get the capacitors discharged) and insert the batteries back. The pairing request is sent on the boot.
All battery operated radio nodes have turned off the radio receiver when they are sleeping. The gateway is listening all the time. This way it is very easy to send data anytime from battery operated node to the gateway.
The other way - communication from gateway to the remote node is a bit tricky. Let's say you would like battery operated node with Relay Module which is bistable and needs energy only when changing its state. There is few solutions for this functionality:
By using Power Module or micro USB cable to power Core Module constantly you can enable in your firmware radion in listening mode BC_RADIO_MODE_NODE_LISTENING.
In the firmware you can set the time that the sleeping node will listen after every send message from Node to the Gateway. You set it by calling bc_radio_set_rx_timeout_for_sleeping_node API.
This way let's say you send the measured temperature every 10 minutes and in your Node-RED or server code you will react to this MQTT temperature message and immediatelly response with MQTT message to toggle the relay. We did some tests and 400 ms is more then enought timeout for Node-RED to send the response MQTT message.
This solution adds to the power consumption and you have to find right ballance between battery life and response time the relay can be switched.
With RTC support in SDK it is possible to synchronize the clock of the nodes and create a firmware that will for example listen for 1 second in every 10 minutes. This way the node does not need to send packet like in previous solution, but it needs to be perfectly time-synchronized with the gateway and Node-RED.
Communication frequency (Europe)
Communication frequency (U.S.)
TX Frequency Deviation
TX Transmit Power
RX Filter Bandwidth
For parts of the world where the ISM band is 915 MHz, you cannot use default 868 MHz communication frequency. During the code compilation you have to pass
BAND parameter to the
make like this:
Right now it is not possible to use
bcf tool because all the firmwares are pre-compiled with 868 MHz band. Make sure you also compile Radio Dongle firmware with this parameter.
Explanation of the fields:
This part is called preamble and consists of alternating sequence of zeroes and ones (32 bits).
This part is called synchronization word and has a fixed value of
This part determines the length of the
DATA plus 1 (
DST field is also counted).
This is destination address (for logic network addressing).
Variable length payload data field.
Checksum calculated over all fields excluding
SYN fields. The polynomial of the CRC engine is