X-Git-Url: https://vault307.fbx.one/gitweb/micorpython_ir.git/blobdiff_plain/f2990bb46017fc3723fdf3d8917f94c458f5ee0a..e5768db31f053f95c6f6ede39346281e78cafb04:/README.md diff --git a/README.md b/README.md index 03e013e..3c78771 100644 --- a/README.md +++ b/README.md @@ -2,114 +2,364 @@ 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 entirely compatible with it. +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 a several mutually -incompatible protocols and at least two options for carrier frequency, namely -36KHz and 38KHz. +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. -The drivers support the NEC protocol 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 so any value may be used. The receiver uses a hardware demodulator -which must be specified for the correct frequency. The device driver is carrier -frequency agnostic. +A remote using the NEC protocol is [this one](https://www.adafruit.com/products/389). -# Hardware Requirements +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. There are two options for carrier frequency: 36KHz and 38KHz. The -chip must be selected for the frequency in use by the remote. +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). -# Decoder for IR Remote Controls using the NEC protocol +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. -This protocol is widely used. An example remote is [this one](https://www.adafruit.com/products/389). -To interface the device 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. +# 3. Installation -The driver and test programs run on the Pyboard and ESP8266. +On import, demos print an explanation of how to run them. -# Files +## 3.1 Receiver - 1. `aremote.py` The device driver. - 2. `art.py` A test program to characterise a remote. - 3. `art1.py` Control an onboard LED using a remote. The data and addresss - values need changing to match your characterised remote. +This is a Python package. This minimises RAM usage: applications only import +the device driver for the protocol in use. -# Dependencies +Copy the following to the target filesystem: + 1. `ir_rx` Directory and contents. Contains the device drivers. + 2. `ir_rx_test.py` Demo of a receiver. -The driver requires the `uasyncio` library and the file `asyn.py` from this -repository. +There are no dependencies. -# Usage +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. -The pin used to connect the decoder chip to the target is arbitrary but the -test programs assume pin X3 on the Pyboard and pin 13 on the ESP8266. +## 3.2 Transmitter -The driver is event driven. Pressing a button on the remote causes a user -defined callback to be run. The NEC protocol returns a data value and an -address. These are passed to the callback as the first two arguments (further -user defined arguments may be supplied). The address is normally constant for a -given remote, with the data corresponding to the button. Applications should -check the address to ensure that they only respond to the correct remote. +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. -Data values are 8 bit. Addresses may be 8 or 16 bit depending on whether the -remote uses extended addressing. +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). -If a button is held down a repeat code is sent. In this event the driver -returns a data value of `REPEAT` and the address associated with the last -valid data block. +# 4. Receiver -To characterise a remote run `art.py` and note the data value for each button -which is to be used. If the address is less than 256, extended addressing is -not in use. +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: -# Reliability +```python +import time +from machine import Pin +from pyb import LED +from ir_rx.nec import NEC_8 # NEC remote, 8 bit addresses -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. So applications must check for, and usually ignore, errors. -These are flagged by data values < `REPEAT`. +red = LED(1) -On the ESP8266 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. This tendency is slightly reduced by -running the chip at 160MHz. +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)) -In general applications should provide user feedback of correct reception. -Users tend to press the key again if no acknowledgement is received. +ir = NEC_8(Pin('X3', Pin.IN), callback) +while True: + time.sleep_ms(500) + red.toggle() +``` + +#### Common to all classes -# The NEC_IR class +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 constructor takes the following positional arguments. +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. - 1. `pin` A `Pin` instance for the decoder chip. - 2. `cb` The user callback function. - 3. `extended` Set `False` to enable extra error checking if the remote - returns an 8 bit address. - 4. Further arguments, if provided, are passed to the callback. +Bound variable: + 1. `verbose=False` If `True` emits debug output. -The callback receives the following positional arguments: +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). - 1. The data value returned from the remote. - 2. The address value returned from the remote. - 3. Any further arguments provided to the `NEC_IR` constructor. +A function is provided to print errors in human readable form. This may be +invoked as follows: -Negative data values are used to signal repeat codes and transmission errors. +```python +from ir_rx.print_error import print_error # Optional print of error codes +# Assume ir is an instance of an IR receiver class +ir.error_function(print_error) +``` -The test program `art1.py` provides an example of a minimal application. +#### NEC classes -# How it works +`NEC_8`, `NEC_16` -The NEC protocol is described in these references. +```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. +![Image](images/circuit.png) + +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. +![Image](images/circuit2.png) + +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 @@ -135,25 +385,3 @@ 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. - -# Error returns - -Data values passed to the callback are normally 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.