-# micropython_ir
-Nonblocking device drivers to receive from IR remotes and for IR "blaster" apps.
+# Device drivers for IR (infra red) remote controls
+
+This repo provides a driver to receive from IR (infra red) remote controls and
+a driver for IR "blaster" apps. The device drivers are nonblocking. They do not
+require `uasyncio` but are compatible with it.
+
+The transmitter driver is specific to the Pyboard. The receiver is cross
+platform and has been tested on Pyboard, ESP8266 and ESP32. See
+[Receiver platforms](./README.md#42-receiver-platforms) for test results and
+limitations.
+
+# 1. IR communication
+
+IR communication uses a carrier frequency to pulse the IR source. Modulation
+takes the form of OOK (on-off keying). There are multiple protocols and at
+least three options for carrier frequency, namely 36KHz, 38KHz and 40KHz.
+
+The drivers support NEC and Sony protocols and two Philips protocols, namely
+RC-5 and RC-6 mode 0. In the case of the transmitter the carrier frequency is a
+runtime parameter: any value may be specified. The receiver uses a hardware
+demodulator which should be purchased for the correct frequency. The receiver
+device driver sees the demodulated signal and is hence carrier frequency
+agnostic.
+
+Examining waveforms from various remote controls it is evident that numerous
+protocols exist. Some are doubtless proprietary and undocumented. The supported
+protocols are those for which I managed to locate documentation. My preference
+is for the NEC version. It has conservative timing and ample scope for error
+detection. RC-5 has limited error detection, and RC-6 mode 0 has rather fast
+timing.
+
+A remote using the NEC protocol is [this one](https://www.adafruit.com/products/389).
+
+Remotes transmit an address and a data byte, plus in some cases an extra value.
+The address denotes the physical device being controlled. The data defines the
+button on the remote. Provision usually exists for differentiating between a
+button repeatedly pressed and one which is held down; the mechanism is protocol
+dependent.
+
+# 2. Hardware Requirements
+
+The receiver is cross-platform. It requires an IR receiver chip to demodulate
+the carrier. The chip must be selected for the frequency in use by the remote.
+For 38KHz devices a receiver chip such as the Vishay TSOP4838 or the
+[adafruit one](https://www.adafruit.com/products/157) is required. This
+demodulates the 38KHz IR pulses and passes the demodulated pulse train to the
+microcontroller. The tested chip returns a 0 level on carrier detect, but the
+driver design ensures operation regardless of sense.
+
+In my testing a 38KHz demodulator worked with 36KHz and 40KHz remotes, but this
+is obviously neither guaranteed nor optimal.
+
+The pin used to connect the decoder chip to the target is arbitrary. The test
+program assumes pin X3 on the Pyboard, pin 23 on ESP32 and pin 13 on ESP8266.
+On the WeMos D1 Mini the equivalent pin is D7.
+
+The transmitter requires a Pyboard 1.x (not Lite) or a Pyboard D. Output is via
+an IR LED which will normally need a transistor to provide sufficient current.
+Typically these need 50-100mA of drive to achieve reasonable range and data
+integrity. A suitable LED is [this one](https://www.adafruit.com/product/387).
+
+The transmitter test script assumes pin X1 for IR output. It can be changed,
+but it must support Timer 2 channel 1. Pins for pushbutton inputs are
+arbitrary: X3 and X4 are used.
+
+# 3. Installation
+
+On import, demos print an explanation of how to run them.
+
+## 3.1 Receiver
+
+This is a Python package. This minimises RAM usage: applications only import
+the device driver for the protocol in use.
+
+Copy the following to the target filesystem:
+ 1. `ir_rx` Directory and contents. Contains device drivers and test script.
+
+There are no dependencies.
+
+The test script may be used to characterise remote controls. To run it issue:
+```python
+from ir_rx import test
+```
+The script will display instructions for running against the various protocols.
+If you are unsure which protocol your remote uses, try each one in turn. If
+none of the options work it may be that an unsupported protocol is in use.
+
+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. Applications should
+instantiate the appropriate class with a callback. The callback will run
+whenever an IR pulse train is received. Example running on a Pyboard:
+
+```python
+import time
+from machine import Pin
+from pyb import LED
+from ir_rx.nec import NEC_8 # NEC remote, 8 bit addresses
+
+red = LED(1)
+
+def callback(data, addr, ctrl):
+ if data < 0: # NEC protocol sends repeat codes.
+ print('Repeat code.')
+ else:
+ print('Data {:02x} Addr {:04x}'.format(data, addr))
+
+ir = NEC_8(Pin('X3', Pin.IN), callback)
+while True:
+ time.sleep_ms(500)
+ red.toggle()
+```
+
+#### 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).
+
+#### NEC classes
+
+`NEC_8`, `NEC_16`
+
+```python
+from ir_rx.nec import NEC_8
+```
+
+Remotes using the NEC protocol can send 8 or 16 bit addresses. If the `NEC_16`
+class receives an 8 bit address it will get a 16 bit value comprising the
+address in bits 0-7 and its one's complement in bits 8-15.
+The `NEC_8` class enables error checking for remotes that return an 8 bit
+address: the complement is checked and the address returned as an 8-bit value.
+A 16-bit address will result in an error.
+
+#### Sony classes
+
+`SONY_12`, `SONY_15`, `SONY_20`
+
+```python
+from ir_rx.sony import SONY_15
+```
+
+The SIRC protocol comes in 3 variants: 12, 15 and 20 bits. `SONY_20` handles
+bitstreams from all three types of remote. Choosing a class matching the 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.
+A single physical remote can issue more than one type of bitstream. The Sony
+remote tested issued both 12 bit and 15 bit streams.
+
+#### Philips classes
+
+`RC5_IR`, `RC6_M0`
+
+```python
+from ir_rx.philips import RC5_IR
+```
+
+These support the RC-5 and RC-6 mode 0 protocols respectively.
+
+# 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
+
+[General information about IR](https://www.sbprojects.net/knowledge/ir/)
+
+The NEC protocol:
+[altium](http://techdocs.altium.com/display/FPGA/NEC+Infrared+Transmission+Protocol)
+[circuitvalley](http://www.circuitvalley.com/2013/09/nec-protocol-ir-infrared-remote-control.html)
+
+Philips protocols:
+[RC5](https://en.wikipedia.org/wiki/RC-5)
+[RC6](https://www.sbprojects.net/knowledge/ir/rc6.php)
+
+Sony protocol:
+[SIRC](https://www.sbprojects.net/knowledge/ir/sirc.php)
+
+# Appendix 1 NEC Protocol description
+
+A normal burst comprises exactly 68 edges, the exception being a repeat code
+which has 4. An incorrect number of edges is treated as an error. All bursts
+begin with a 9ms pulse. In a normal code this is followed by a 4.5ms space; a
+repeat code is identified by a 2.25ms space. A data burst lasts for 67.5ms.
+
+Data bits comprise a 562.5µs mark followed by a space whose length determines
+the bit value. 562.5µs denotes 0 and 1.6875ms denotes 1.
+
+In 8 bit address mode the complement of the address and data values is sent to
+provide error checking. This also ensures that the number of 1's and 0's in a
+burst is constant, giving a constant burst length of 67.5ms. In extended
+address mode this constancy is lost. The burst length can (by my calculations)
+run to 76.5ms.
+
+A pin interrupt records the time of every state change (in µs). The first
+interrupt in a burst sets an event, passing the time of the state change. A
+coroutine waits on the event, yields for the duration of a data burst, then
+decodes the stored data before calling the user-specified callback.
+
+Passing the time to the `Event` instance enables the coro to compensate for
+any asyncio latency when setting its delay period.
+
+The algorithm promotes interrupt handler speed over RAM use: the 276 bytes used
+for the data array could be reduced to 69 bytes by computing and saving deltas
+in the interrupt service routine.
projects / micorpython_ir.git / blobdiff