nRF24L01+ C LIBRARY

• version 1.0
• Reza Ebrahimi

This library is written in portable C, and is MCU independent. It consumes a small amount of RAM (under 50 bytes) and program memory (under 2 KB). In order to implement it to your MCU of choice, you need to manipulate functions inside nrf24l01_low_level.c file (SPI, pin configurations) and leave other files as they are.

nRF24L01+ C library abstracts away the internals of the hardware, using LEVEL 4 functions (description below).

This library is written based on the nRF24L01+ Preliminary Product Specification released by Nordic Semiconductor and is not influenced by other (probably numorous) libraries out there. Any resemblance to pre-existing code is unintentional.

You can use this library in any way, shape or form. I'd be very happy if you mention my name though.

HOW TO USE

As mentioned earlier, first you need to implement low level settings like SPI, delay function and pin configurations inside nrf24l01_low_level.c file (LEVEL 1).

Start by calling nrf24_device(uint8_t device_mode, uint8_t reset_state) function. You can set the device mode to either TRANSMITTER, RECEIVER, POWER_SAVING or TURN_OFF and reset_state to RESET or NO_RESET. if this is the first time nrf24_device is called, nrf24l01+ is reset regardless of reset_state. nrf24_device initializes the low level API like SPI etc, and sets nrf24l01+ with default values and settings. These settings and values can be changed with manipulating macros inside nrf24l01.h, or by calling LEVEL 3 functions. the next steps depend on the chosen device_mode.

For TRANSMITTER: Use nrf24_transmit(uint8_t *payload, uint8_t payload_width, uint8_t acknowledgement_state) to send an array of 1 byte blocks, with the specified payload_width and acknowledgement_state (could be ACK_MODE or NO_ACK_MODE). If nrf24l01+ is set to static payload width, payload_width is ignored. nrf24_transmit has 2 different outputs: TRANSMIT_BEGIN and TRANSMIT_FAIL (in case of wrong mode of operation or full TX FIFO buffer). Next, you can use nrf24_transmit_status() which has no input, but gives back status: TRANSMIT_IN_PROGRESS if the payload is still not sent or if TX buffer is empty, TRANSMIT_DONE if the payload is sent successfully, TRANSMIT_FAILED if the payload has reached he maximum number of retransmits (only in ACK_MODE).

For RECEIVER: nrf24_receive(uint8_t *payload, uint8_t payload_width) can be used to both poll the RX buffer, and receive the payload if its already inside the buffer. payload_width is ignored if nrf24l01+ was set to static payload width mode. nrf24_receive outputs the polling results as: OPERATION_ERROR if not in RECEIVER mode, RECEIVE_FIFO_EMPTY in case of empty buffer (payload array is not updated) and OPERATION_DONE if the received data is saved inside payload array.

For POWER_SAVING or TURN_OFF: You cannot send or receive any data in these modes of operation, these are used only to reduce power consumption. device_mode can be changed mid code.

General considerations: the default value for transmit radio power is set to -6 dbm. the default value for radio channel is set to channel 32. the default payload width is 1 byte and its static. the default value for datarate is 1Mbps.

HOW IT WORKS

Functions can be categorized into different levels: from low level APIs up to higher ones. Lower level APIs are used by higher level APIs. Use LEVEL 4 functions (or sometimes LEVEL 3, if you want to change settings) in your firmware.

LEVEL 1:

• void delay_function(uint32_t duration_ms)
• void SPI_Initializer()
• void pinout_Initializer()
• void nrf24_SPI(uint8_t input)
• uint8_t SPI_send_command(uint8_t command)
• void nrf24_CE(uint8_t input)

LEVEL 2:

• void nrf24_write(uint8_t address, uint8_t *value, uint8_t data_length, uint8_t spi_state)
• void nrf24_read(uint8_t address, uint8_t *value, uint8_t data_length, uint8_t spi_state)
• void nrf24_send_payload(uint8_t *payload, uint8_t payload_width)

LEVEL 3:

• void nrf24_mode(uint8_t mode)
• void nrf24_crc_configuration(uint8_t crc_enable, uint8_t crc_encoding_scheme)
• void nrf24_interrupt_mask(uint8_t rx_mask, uint8_t tx_mask, uint8_t max_rt_mask)
• void nrf24_rf_channel(uint8_t rf_channel)
• void nrf24_rf_power(uint8_t rf_power)
• void nrf24_rf_datarate(uint8_t rf_datarate)
• void nrf24_address_width(uint8_t address_width)
• void nrf24_datapipe_enable(uint8_t number_of_datapipes)
• void nrf24_prx_static_payload_width(uint8_t static_payload_width, uint8_t number_of_datapipes)
• void nrf24_datapipe_address_configuration()
• void nrf24_datapipe_ptx(uint8_t datapipe_number)
• void nrf24_dynamic_payload(uint8_t state, uint8_t datapipe)
• void nrf24_auto_acknowledgment_setup(uint8_t datapipe)
• void nrf24_automatic_retransmit_setup(uint16_t delay_time, uint8_t retransmit_count)
• void nrf24_dynamic_ack(uint8_t state)

LEVEL 4:

• void nrf24_device(uint8_t device_mode, uint8_t reset_state)
• void nrf24_reset()
• uint8_t nrf24_flush(uint8_t fifo_select)
• uint8_t nrf24_receive(uint8_t *payload, uint8_t payload_width)
• uint8_t nrf24_transmit_status()
• uint8_t nrf24_transmit(uint8_t *payload, uint8_t payload_width, uint8_t acknowledgement_state)

EXAMPLE

As an example, a simple byte transmitter for arduino/atmega boards is provided.