New-Tech Europe Magazine | Aug 2018

possible to set temperatures on all the devices with the same network (multicast) address. As usual, setting up the address involves one command over UART. For example, setting the source network address to 0x01, we use the CMD_SET_REQ (0x09) command with the settings index MAC_SourceNetID (0x0B) and the parameter 0x01. S t a r t signal Command Length Settings Index Parameter CS 0x02 0x09 0x02 0x0B 0x01 0x03 ACK and retries Reliability in communication, especially, in hostile industrial environments requires redundancy. The AMB8826 supports an acknowledgment-retry mechanism where the user data packet is re-sent if the receiver does not acknowledge the receipt of a data packet within a specified time. For the cooling application, with the ACK turned on, the remote host can be sure that the module on-site has received its instructions to increase the fan speed to 1000 rpm. This can be achieved by simply setting the MAC_NumRetrys parameter (with index 0x06) by sending the CMD_SET_REQ(0x09) command with the parameter 0x01. S t a r t signal Command Length Settings Index Parameter CS 0x02 0x09 0x02 0x06 0x01 0x0E Repeater and Mesh network The repeater mode of the AMB8826 offers several benefits including range extension, dead-zone coverage as well as flooding mesh feature. Due to the physical properties of radio wave propagation, it is not always possible to offer full coverage, especially in indoor industrial environments. With the AMB8826 configured in repeater mode, the module simply forwards a packet after a random back-off time. With several nodes in a given neighborhood configured as repeaters, each of them forward packets not addressed to themselves creating a flooding mesh network. Inherently, such networks are simple,

error correction. The available spectrum in both the 868 MHz as well as the 915 MHz band are divided into grids with channel numbers ranging from 100 -140 and 200-252 respectively. This allows the possibility to precisely define the frequency of operation and choose the optimal channel with least congestion. The third pillar of RF link, the transmitting power, is also configurable from 0-14 dBm in steps of 1 dBm completing a fully flexible physical layer configuration. Changing the radio profile, operating channel and transmitting power involves sending a single command over the UART against complex calculations of multiple register values. For example, setting the RF power to +14 dBm (0x0E in hex) uses the following command. Network Creating a wireless network is often essential when multiple radios are collocated, sharing the same radio channel. In the case of our temperature monitoring examples, let us assume that in a large industrial complex, multiple machines are fitted with our wireless temperature monitoring system. The central host, which controls all these systems, receives temperature data from all these systems. Now, the question is which temperature belongs to which machine. To address this issue, the AMB8826 allows allocation of up to 3-byte addresses to each module. Based on the mode of addressing, the AMB8826 module can have 0/1- byte network address and 0/1/2- byte device address. Having a byte reserved for the network address allows the possibility of multicast and broadcast messages. What this means in terms of our sensor application is that, with a single multicast message, it would be S t a r t signal Command Length Power CS 0x02 0x11 0x01 0x0E 1C

Start signal Command Length Payload

CS

0x1C

0x02

0x00

0x16 0x53 0x45 0x54 0x20 0x54 0x45 0x4d 0x50 0x20 0x35 0x35 0x20 0x53 0x50 0x45 0x45 0x44 0x20 0x31 0x30 0x30 0x30

The module itself then responds with the following confirmation to the remote host. Start signal Command | 0x40 Length Status CS 0x02 0x40 0x01 0x00 0x43 The on-board microcontroller receives this message and sets the thresholds accordingly. From, the example above it is clear that with a very simple command interface, messages could be exchanged easily between the two or more stations. Step 3: Certification The AMB8826 and its counterpart AMB9826 operate in the unlicensed 868 MHz and the 915 MHz bands respectively. “Unlicensed” does not mean “unregulated”, and every device that uses this spectrum has to conform to the local spectrum regulations. The good news here is that the AMB8826/AMB9826 comes pre-certified to RED, FCC and IC standards. What this means for our industrial temperature controller application is that the end product can be certified in Europe and North America with minimum effort, money and time. Radio configuration Flexibility in physical layer configuration is very important to tailor to the needs of the application. Some applications require higher data throughput while other may require greater range. Catering specifically to these requirements, the AMB8826 offers six different radio profiles. At one extreme, a high data rate of 400 Kbit/s with 224- byte payload is available for bandwidth- hungry applications. On the other hand, apt for hostile industrial environments, long-range mode offers reliable transfer of small 48-byte packets with forward

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