-# 3. Installation
-
-On import, demos print an explanation of how to run them.
-
-## 3.1 Receiver
-
-Copy the following files to the target filesystem:
- 1. `ir_rx.py` The receiver device driver.
- 2. `ir_rx_test.py` Demo of a receiver.
-
-There are no dependencies.
-
-The demo can be used to characterise IR remotes. It displays the codes returned
-by each button. This can aid in the design of receiver applications. The demo
-prints "running" every 5 seconds and reports any data received from the remote.
-
-## 3.2 Transmitter
-
-Copy the following files to the Pyboard filesystem:
- 1. `ir_tx.py` The transmitter device driver.
- 2. `ir_tx_test.py` Demo of a 2-button remote controller.
-
-The device driver has no dependencies. The test program requires `uasyncio`
-from the official library and `aswitch.py` from
-[this repo](https://github.com/peterhinch/micropython-async).
-
-# 4. Receiver
-
-This implements a class for each supported protocol, namely `NEC_IR`,
-`SONY_IR`, `RC5_IR` and `RC6_M0`. Applications should instantiate the
-appropriate class with a callback. The callback will run whenever an IR pulse
-train is received.
-
-#### Common to all classes
-
-Constructor:
-Args:
- 1. `pin` is a `machine.Pin` instance configured as an input, connected to the
- IR decoder chip.
- 2. `callback` is the user supplied callback.
- 3. `*args` Any further args will be passed to the callback.
-
-The user callback takes the following args:
- 1. `data` (`int`) Value from the remote. Normally in range 0-255. A value < 0
- signifies an NEC repeat code.
- 2. `addr` (`int`) Address from the remote.
- 3. `ctrl` (`int`) The meaning of this is protocol dependent:
- NEC: 0
- Philips: this is toggled 1/0 on repeat button presses. If the button is held
- down it is not toggled. The transmitter demo implements this behaviour.
- Sony: 0 unless receiving a 20-bit stream, in which case it holds the extended
- value.
- 4. Any args passed to the constructor.
-
-Bound variable:
- 1. `verbose=False` If `True` emits debug output.
-
-Method:
- 1. `error_function` Arg: a function taking a single arg. If this is specified
- it will be called if an error occurs. The value corresponds to the error code
- (see below).
-
-#### Properties specific to a class
-
-`NEC_IR`:
-`extended` `bool`. Remotes using the NEC protocol can send 8 or 16 bit
-addresses. If `True` 16 bit addresses are assumed. If an 8 bit address is sent
-it will be received as a 16 bit value comprising the address and (in bits 8-15)
-its ones complement. Set `False` to enable error checking for remotes that
-return an 8 bit address: the complement will be checked and the address will be
-returned as an 8-bit value. The default is `True`.
-
-`SONY_IR`:
-`bits` `int`. The SIRC protocol comes in 3 variants: 12, 15 and 20 bits. The
-default will handle bitstreams from all three types of remote. A value matching
-your remote improves the timing reducing the likelihood of errors when handling
-repeats: in 20-bit mode SIRC timing when a button is held down is tight. A
-worst-case 20-bit block takes 39ms nominal, yet the repeat time is 45ms nominal.
-The Sony remote tested issues both 12 bit and 15 bit streams. The default is
-20.
-
-# 4.1 Errors
-
-IR reception is inevitably subject to errors, notably if the remote is operated
-near the limit of its range, if it is not pointed at the receiver or if its
-batteries are low. The user callback is not called when an error occurs.
-
-On ESP8266 and ESP32 there is a further source of errors. This results from the
-large and variable interrupt latency of the device which can exceed the pulse
-duration. This causes pulses to be missed or their timing measured incorrectly.
-On ESP8266 some improvment may be achieved by running the chip at 160MHz.
-
-In general applications should provide user feedback of correct reception.
-Users tend to press the key again if the expected action is absent.
-
-In debugging a callback can be specified for reporting errors. The value passed
-to the error function are represented by constants indicating the cause of the
-error. These are as follows:
-
-`BADSTART` A short (<= 4ms) start pulse was received. May occur due to IR
-interference, e.g. from fluorescent lights. The TSOP4838 is prone to producing
-200µs pulses on occasion, especially when using the ESP8266.
-`BADBLOCK` A normal data block: too few edges received. Occurs on the ESP8266
-owing to high interrupt latency.
-`BADREP` A repeat block: an incorrect number of edges were received.
-`OVERRUN` A normal data block: too many edges received.
-`BADDATA` Data did not match check byte.
-`BADADDR` (`NEC_IR`) If `extended` is `False` the 8-bit address is checked
-against the check byte. This code is returned on failure.
-
-# 4.2 Receiver platforms
-
-Currently the ESP8266 suffers from [this issue](https://github.com/micropython/micropython/issues/5714).
-Testing was therefore done without WiFi connectivity.
-
-Philips protocols (especially RC-6) have tight timing constraints with short
-pulses whose length must be determined with reasonable accuracy. The Sony 20
-bit protocol also has a timing issue in that the worst case bit pattern takes
-39ms nominal, yet the repeat time is 45ms nominal. These issues can lead to
-errors particularly on slower targets. As discussed above, errors are to be
-expected. It is up to the user to decide if the error rate is acceptable.
-
-Reception was tested using Pyboard D SF2W, ESP8266 and ESP32 with signals from
-remote controls (where available) and from the tranmitter in this repo. Issues
-are listed below.
-
-NEC: No issues.
-Sony 12 and 15 bit: No issues.
-Sony 20 bit: On ESP32 some errors occurred when repeats occurred.
-Philips RC-5: On ESP32 with one remote control many errors occurred, but paired
-with the transmitter in this repo it worked.
-Philips RC-6: No issues. Only tested against the transmitter in this repo.
-
-# 4.3 Principle of operation
-
-Protocol classes inherit from the abstract base class `IR_RX`. This uses a pin
-interrupt to store in an array the start and end times of pulses (in μs).
-Arrival of the first pulse triggers a software timer which runs for the
-expected duration of an IR block (`tblock`). When it times out its callback
-(`.decode`) decodes the data and calls the user callback. The use of a software
-timer ensures that `.decode` and the user callback can allocate.
-
-The size of the array and the duration of the timer are protocol dependent and
-are set by the subclasses. The `.decode` method is provided in the subclass.
-
-CPU times used by `.decode` (not including the user callback) were measured on
-a Pyboard D SF2W at stock frequency. They were: NEC 1ms for normal data, 100μs
-for a repeat code. Philips codes: RC-5 900μs, RC-6 mode 0 5.5ms.
-
-# 5 Transmitter
-
-This is specific to Pyboard D and Pyboard 1.x (not Lite).
-
-It implements a class for each supported protocol, namely `NEC`, `SONY`, `RC5`
-and `RC6_M0`. The application instantiates the appropriate class and calls the
-`transmit` method to send data.
-
-Constructor
-All constructors take the following args:
- 1. `pin` An initialised `pyb.Pin` instance supporting Timer 2 channel 1: `X1`
- is employed by the test script. Must be connected to the IR diode as described
- below.
- 2. `freq=default` The carrier frequency in Hz. The default for NEC is 38000,
- Sony is 40000 and Philips is 36000.
- 3. `verbose=False` If `True` emits debug output.
-
-The `SONY` constructor is of form `pin, bits=12, freq=40000, verbose=False`.
-The `bits` value may be 12, 15 or 20 to set SIRC variant in use. Other args are
-as above.
-
-Method:
- 1. `transmit(addr, data, toggle=0)` Integer args. `addr` and `data` are
- normally 8-bit values and `toggle` is normally 0 or 1.
- In the case of NEC, if an address < 256 is passed, normal mode is assumed and
- the complementary value is appended. 16-bit values are transmitted as extended
- addresses.
- In the case of NEC the `toggle` value is ignored. For Philips protocols it
- should be toggled each time a button is pressed, and retained if the button is
- held down. The test program illustrates a way to do this.
- `SONY` ignores `toggle` unless in 20-bit mode, in which case it is transmitted
- as the `extended` value and can be any integer in range 0 to 255.
-
-The `transmit` method is synchronous with rapid return. Actual transmission
-occurs as a background process, controlled by timers 2 and 5. Execution times
-on a Pyboard 1.1 were 3.3ms for NEC, 1.5ms for RC5 and 2ms for RC6.
-
-# 5.1 Wiring
-
-I use the following circuit which delivers just under 40mA to the diode. R2 may
-be reduced for higher current.
-
-
-This alternative delivers a constant current of about 53mA if a higher voltage
-than 5V is available. R4 determines the current value and may be reduced to
-increase power.
-
-
-The transistor type is not critical.
-
-The driver assumes circuits as shown. Here the carrier "off" state is 0V,
-which is the driver default. If using a circuit where "off" is required to be
-3.3V, the constant `_SPACE` in `ir_tx.py` should be changed to 100.
-
-# 5.2 Principle of operation
-
-The classes inherit from the abstract base class `IR`. This has an array `.arr`
-to contain the duration (in μs) of each carrier on or off period. The
-`transmit` method calls a `tx` method of the subclass which populates this
-array. On completion `transmit` appends a special `STOP` value and initiates
-physical transmission which occurs in an interrupt context.
-
-This is performed by two hardware timers initiated in the constructor. Timer 2,
-channel 1 is used to configure the output pin as a PWM channel. Its frequency
-is set in the constructor. The OOK is performed by dynamically changing the
-duty ratio using the timer channel's `pulse_width_percent` method: this varies
-the pulse width from 0 to a duty ratio passed to the constructor. The NEC
-protocol defaults to 50%, the Sony and Philips ones to 30%.
-
-The duty ratio is changed by the Timer 5 callback `._cb`. This retrieves the
-next duration from the array. If it is not `STOP` it toggles the duty cycle
-and re-initialises T5 for the new duration.
-
-The `IR.append` enables times to be added to the array, keeping track of the
-notional carrier on/off state for biphase generation. The `IR.add` method
-facilitates lengthening a pulse as required in the biphase sequences used in
-Philips protocols.
-
-# 6. References
projects / micorpython_ir.git / blobdiff