-In general applications should provide user feedback of correct reception.
-Users tend to press the key again if the expected action is absent.
-
-Data values passed to the callback are zero or positive. Negative values
-indicate a repeat code or an error.
-
-`REPEAT` A repeat code was received.
-
-Any data value < `REPEAT` denotes an error. In general applications do not
-need to decode these, but they may be of use in debugging. For completeness
-they are listed below.
-
-`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` Where `extended` is `False` the 8-bit address is checked
-against the check byte. This code is returned on failure.
-
-# 4.2 Receiver platforms
-
-The NEC protocol has been tested against Pyboard, ESP8266 and ESP32 targets.
-The Philips protocols - especially RC-6 - have tighter timing constraints. I
-have not yet tested these, but I anticipate problems.
-
-# 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