RMT

The RMT (Remote Control) module is primarily designed to send and receive infrared remote control signals that use on-off-keying of a carrier frequency, but due to its design it can be used to generate various types of signals.

Quick Usage Example: sending

import machine

# create a RMT object for transmission
rmt = machine.RMT(channel=3, gpio="P20", tx_idle_level=0)
# create series of bits to send    
data = (1,0,1,0,1,0,1,0,1)
# define duration of the bits, time unit depends on the selected RMT channel  
duration = 10000
# send the signal                                         
rmt.send_pulses(duration, data)

Quick Usage Example: receiving

import machine
# create a RMT object
rmt = machine.RMT(channel=3)
# Configure RTM for receiving
rmt.init(gpio="P20", rx_idle_threshold=12000)     
# wait for any number of pulses until one longer than rx_idle_threshold        
data = rmt.recv_pulses()

Constructors

class machine.RMT(channel, …)

Construct an RMT object on the given channel. channel can be 2-7. With no additional parameters, the RMT object is created but not initialised. If extra arguments are given, the RMT is initialised for transmission or reception. See init for parameters of initialisation. The resolution which a pulse can be sent/received depends on the selected channel:

Methods

rmt.init(gpio, {rx_idle_threshold, [rx_filter_threshold]} / {tx_idle_level, [tx_carrier]})

Initialise the RMT peripheral with the given parameters:

• gpio is the GPIO Pin to use.
• rx_idle_threshold is the maximum duration of a valid pulse. The represented time unit (resolution) depends on the selected channel, value can be 0-65535.
• rx_filter_threshold is the minimum duration of a valid pulse. The represented time unit (resolution) depends on the selected channel, value can be 0-31.
• tx_idle_level is the output signal’s level after the transmission is finished, can be RMT.HIGH or RMT.LOW.
• tx_carrier is the modulation of the pulses to send.

Either rx_idle_threshold or tx_idle_level must be defined, both cannot be given at the same time because a channel can be configured in RX or TX mode only. rx_filter_threshold is not mandatory parameter. If not given then all pulses are accepted with duration less than rx_idle_threshold. tx_carrier is not mandatory parameters. If not given no modulation is used on the sent pulses.

The tx_carrier parameter is a tuple with the following structure:

• carrier_freq_hz is the carrier’s frequency in Hz.
• carrier_duty_percent is the duty percent of the carrier’s signal, can be 0%-100%.
• carrier_level is the level of the pulse to modulate, can be RMT.HIGH or RMT.LOW.

rmt.deinit()

Deinitialise the RMT object.

If an RMT object needs to be reconfigured from RX/TX to TX/RX, then either first deinit() must be called or the init() again with the desired configuration.

rmt.pulses_get([pulses, timeout=MAX_DELAY])

Reads in pulses from the GPIO pin. Can only be used in RX mode

• pulses is the amount of pusles read, ignoring anything shorter than rx_filter_threshold or longer than rx_idle_threshold. if not specified, this function will keep reading pulses until the rx_idle_threshold is exceeded.

• timeout is specified, this function will return if the first pulse does not occur within timeout microseconds. If not specified, it will wait indefinitely.

Return value: Tuple of items with the following structure: (level, duration):

• level represents the level of the received bit/pulse, can be 0 or 1.
• duration represents the duration of the received pulse, the time unit (resolution) depends on the selected channel.

A maximum of 128 pulses can be received in a row without receiving “idle” signal. If the incoming pulse sequence contains more than 128 pulses the rest is dropped and the receiver waits for another sequence of pulses. The pulses_get function can be called to receive more than 128 pulses, however the above mentioned limitation should be kept in mind when evaluating the received data.

rmt.pulses_send(duration, [data, start_level])

Generates pulses as defined by the parameters below. can only be used in TX mode

• duration represents the duration of the pulses to be sent, the time unit (resolution) depends on the selected channel.
• data Tuple that represents the sequence of pulses to be sent, must be composed of 0 or 1 elements.
• start_level defines the state (HIGH/LOW) of the first pulse given by duration if data is not given.

data must be a tuple and duration can be a tuple or a single number, with data being optional. In the case that only duration is provided, it must be a tuple and you must also provide start_level which will dictate the level of the first duration, the signal level then toggles between each duration value. If data is provided and duration is a single number, each pulse in data will have have an equal length as set by duration. If data and duration are provided as tuples, they must be of the same number of elements, with each pulse lasting its matching duration.

Constants

• Define the level of the pulse: RMT.LOW, RMT.HIGH