X-Git-Url: https://vault307.fbx.one/gitweb/micorpython_ir.git/blobdiff_plain/e5768db31f053f95c6f6ede39346281e78cafb04..36140aa568d4a538adafb03e575b26de8a0784ef:/README.md?ds=sidebyside diff --git a/README.md b/README.md index 3c78771..371615f 100644 --- a/README.md +++ b/README.md @@ -2,20 +2,24 @@ 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. +require `uasyncio` but are compatible with it, and are designed for standard +firmware builds. -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. +The receiver is cross platform and has been tested on Pyboard, ESP8266 and +ESP32. The transmitter driver is compatible with Pyboard (1.x and D series) and +also (subject to limitations) with ESP32. For the transmitter a Pyboard is +recommended. + +The transmitter is documented [here](./TRANSMITTER.md) and the receiver is +[here](./RECEIVER.md). # 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. +least three options for carrier frequency: 36, 38 and 40KHz. -The drivers support NEC and Sony protocols and two Philips protocols, namely +The drivers support NEC and Sony protocols plus 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 @@ -25,7 +29,7 @@ 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 +is for the NEC version. It has conservative timing and good provision for error detection. RC-5 has limited error detection, and RC-6 mode 0 has rather fast timing. @@ -39,349 +43,20 @@ dependent. # 2. Hardware Requirements +These are discussed in detail in the relevant docs; the following provides an +overview. + 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. +microcontroller. 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 the device drivers. - 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. 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). - -A function is provided to print errors in human readable form. This may be -invoked as follows: - -```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) -``` - -#### 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. -![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 -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. +The transmitter requires a Pyboard 1.x (not Lite), a Pyboard D or an ESP32. +Output is via an IR LED which will need a transistor to provide sufficient +current. The ESP32 has significant limitations as a transmitter discussed +[here](./TRANSMITTER.md#52-esp32).