X-Git-Url: https://vault307.fbx.one/gitweb/micorpython_ir.git/blobdiff_plain/8ed1c53cbe389c2ee8a30dfa17853199fed4ae49..3618d67b4e6c865ea946e2011acc5dee8b3f8ecb:/README.md diff --git a/README.md b/README.md index b35bd20..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. @@ -39,295 +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 - -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. - -Constructor: -`NEC_IR` args: `pin`, `callback`, `extended=True`, `*args` -`SONY_IR` args: `pin`, `callback`, `bits=20`, `*args` -`RC5_IR` and `RC6_M0`: args `pin`, `callback`, `*args` - -Args (all protocols): - 1. `pin` is a `machine.Pin` instance configured as an input, connected to the - IR decoder chip. - 2. `callback` is the user supplied callback (see below). - 4. `*args` Any further args will be passed to the callback. - -Protocol specific args: - 1. `extended` NEC specific `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. - 2. `bits=20` Sony specific `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 callback takes the following args: - 1. `data` (`int`) Value from the remote. A negative value indicates an error - except for the value of -1 which signifies an NEC repeat code (see below). - 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. - -Class variable: - 1. `verbose=False` If `True` emits debug output. - -# 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 should check for, and usually ignore, -errors. These are flagged by data values < `REPEAT` (-1). - -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. - -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` (-1) 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 - -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).