arduino microcontroller and nrf24l01+ transceivers
TRANSCRIPT
Arduino microcontroller and nRF24L01+ transceivers
Pavlos Kallis
Supervisor : prof. Leandros Tassiulas
University of Thessaly
Network implementation testbed laboratory (NITLAB)
Purpose
Deployment of a wireless sensor network using arduino microcontrollers and nRF24L01+
transceivers
Wireless sensor network
● Nodes receive measurements through sensors
● Nodes forward measurements to a central node
Arduino Leonardo
NRF24L01+ Transceiver
RF24L01+ TransceiverΝ
Low CostAlternative to Xbee
NRF24L01+ Transceiver
Data Rates: 250 kbps, 1 Mbps, 2 Mbps
NRF24L01+ Transceiver
Frequency: 2400-2525 MHz
NRF24L01+ Transceiver
Channels : 126
NRF24L01+ Transceiver
Modulation: GSFK
NRF24L01+ Transceiver
Line-of-sight range : ~40m
NRF24L01+ Transceiver
Channel sensing
NRF24L01+ TX/RX
● Auto packet assembly
● Auto ACKs and retransmissions
– Configurable # of retries
– Configurable delay between retries
NRF24L01+ Packet structure
NRF24L01+ pipes
Transmitter Receiver
Pipe
Write 0x01
Read 0x01
NRF24L01+ pipes
ReceiverPipe
Read 0x05Pipe
Pipe
Pipe
Pipe
Read 0x04
Read 0x03
Read 0x02
Read 0x01
Write 0x01
Write 0x05
Write 0x04
Write 0x03
Write 0x02
Transmitters
RF24 library
● Software for Point-to-point communication between nRF24L01+ transceivers
● Abstracts low-level communication between the microcontroller and the transceiver
RF24 libraryconfiguration
● Channel● Payload size● Data rate● ACKs or no● Retry delay● Number of retries● CRC length
Schematic to connect arduino leonardo with nRF24L01+ transceivers
RF24 Library example setup
1) Ping role sends its
timestamp
2) Pong role replies with timestamp
3) Ping role calculates round-trip
time
Ping RolePong role
RF24 Library transmission mechanism
● When two transmitters send a packet simultaneously
RF24 Library transmission mechanism
● When two transmitters send a packet simultaneously
– A collision occurs
TX
RX
TX
RF24 Library transmission mechanism
● When two transmitters send a packet simultaneously
– A collision occurs
– Receiver cannot decode the message
TX
RX
TX
RF24 Library transmission mechanism
● When two transmitters send a packet simultaneously
– A collision occurs
– Receiver cannot decode the message
– The transmitters will retry in the SAME time slots
– Until maximum no. of retries reached
Proposed mechanism
● If a transmitter fails to transmit a packet(no ack received)
– It will wait for a random period, then retransmit
Proposed mechanism
● If a transmitter fails to transmit a packet(no ack received)
– It will wait for a random period, then retransmit
– The random period is selected from a contention window, that is doubled every time the TX fails to transmit a packet
Proposed mechanism
● If a transmitter fails to transmit a packet(no ack received)
– It will wait for a random period, then retransmit
– The random period is selected from a contention window, that is doubled every time the TX fails to transmit a packet
– Until the maximum number of retries is exceeded
Proposed mechanism : Implementation
● Disabled the retransmission mechanism by calling setRetries(0, 0)
● Built on top of write(buf, len)
Proposed mechanism : Implementation
● Problem : The function write was poweringDown() the transmitter after a packet transmission
– Increased delay to wake ( 1.5 ms)
– Our random backoff time was much less than that
● Solution : We disabled the powerDown() function
RF24Network Library
● Network layer software library for nRF24L01+ transceivers
● Built on top of RF24 library● Handles transmissions in network layer
RF24Network Library
● Tree topology– Max no. of children = 5
WSN Addressing
WSN Setup
Base Node
Relay Node
Leaf Node
Thank you