TRANSMITTER.md: remove dubious MOSFET idea.

[micorpython_ir.git] / TRANSMITTER.md

diff --git a/TRANSMITTER.md b/TRANSMITTER.md
index 3478ba83e7bf30020be416a60fcd222c6d1f65b0..24cd24423b22c16bcd125372837dba657cbee883 100644 (file)
--- a/TRANSMITTER.md
+++ b/TRANSMITTER.md
@@ -5,7 +5,7 @@
 # 1. Hardware Requirements
 
 The transmitter requires a Pyboard 1.x (not Lite), a Pyboard D or an ESP32.
 # 1. Hardware Requirements
 
 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
+Output is via an IR LED which needs a simple circuit to provide sufficient

 current. Typically these need 50-100mA of drive to achieve reasonable range and
 data integrity. A suitable 940nm LED is [this one](https://www.adafruit.com/product/387).
 
 current. Typically these need 50-100mA of drive to achieve reasonable range and
 data integrity. A suitable 940nm LED is [this one](https://www.adafruit.com/product/387).
 


@@ -13,10 +13,10 @@ On the Pyboard 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. The driver uses timers 2 and 5.
 
 be changed, but it must support Timer 2 channel 1. Pins for pushbutton inputs
 are arbitrary: X3 and X4 are used. The driver uses timers 2 and 5.
 

-On ESP32 pin 23 is used for IR output and pins 18 and 19 for pushbuttons. The
-ESP32 solution has limitations discussed in [section 5.2](./TRANSMITTER.md#52-esp32).
+On ESP32 the demo uses pins 21 and 23 for IR output and pins 18 and 19 for
+pushbuttons. These pins may be changed.

 
 

-## 1.1 Wiring
+## 1.1 Pyboard Wiring

 
 I use the following circuit which delivers just under 40mA to the diode. R2 may
 be reduced for higher current.  
 
 I use the following circuit which delivers just under 40mA to the diode. R2 may
 be reduced for higher current.  


@@ -33,20 +33,37 @@ 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.__init__.py` should be changed to 100.
 
 which is the driver default. If using a circuit where "off" is required to be
 3.3V, the constant `_SPACE` in `ir_tx.__init__.py` should be changed to 100.
 

-# 2. Installation
+## 1.2 ESP32 Wiring

 
 

-The transmitter is a Python package. This minimises RAM usage: applications
-only import the device driver for the protocol in use.
+The ESP32 RMT device does not currently support the carrier option. A simple
+hardware gate is required to turn the IR LED on when both the carrier pin and
+the RMT pin are high. A suitable circuit is below.  
+![Image](images/gate.png)

 
 

-Copy the following to the target filesystem:
- 1. `ir_tx` Directory and contents.
+The transistor type is not critical.
+
+# 2. Dependencies and installation
+
+## 2.1 Dependencies

 
 The device driver has no dependencies.
 
 
 The device driver has no dependencies.
 

+On ESP32 a firmware version >= V1.12 is required. The Loboris port is not
+supported owing to the need for the RMT device.
+

 The demo program requires `uasyncio` from the official library and `aswitch.py`
 The demo program requires `uasyncio` from the official library and `aswitch.py`

-from [this repo](https://github.com/peterhinch/micropython-async). The demo is
-of a 2-button remote controller with auto-repeat. It may be run by issuing:
+from [this repo](https://github.com/peterhinch/micropython-async).

 
 

+## 2.2 Installation
+
+The transmitter 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_tx` Directory and contents.
+
+The demo is of a 2-button remote controller with auto-repeat. It may be run by
+issuing:

 ```python
 from ir_tx.test import test
 ```
 ```python
 from ir_tx.test import test
 ```


@@ -61,18 +78,16 @@ It implements a class for each supported protocol, namely `NEC`, `SONY_12`,
 common abstract base class in `__init__.py`. The application instantiates the
 appropriate class and calls the `transmit` method to send data.
 
 common abstract base class in `__init__.py`. The application instantiates the
 appropriate class and calls the `transmit` method to send data.
 

-The ESP32 platform is marginal in this application because of imprecision in
-its timing. The Philips protocols are unsupported as they require unachievable
-levels of precision. Test results are discussed [here](./TRANSMITTER.md#52-esp32).
+#### Common to all classes

 
 

-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.
+Constructor args:  
+ 1. `pin` A Pin instance instantiated as an output. On a Pyboard this is a
+ `pyb.Pin` instance supporting Timer 2 channel 1: `X1` is employed by the test
+ script. On ESP32 any `machine.Pin` may be used. 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.
  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.
+ 3. `verbose=False` If `True` emits (a lot of) debug output.

 
 Method:
  1. `transmit(addr, data, toggle=0)` Integer args. `addr` and `data` are
 
 Method:
  1. `transmit(addr, data, toggle=0)` Integer args. `addr` and `data` are


@@ -93,9 +108,9 @@ The NEC protocol accepts 8 or 16 bit addresses. In the former case, a 16 bit
 value is transmitted comprising the 8 bit address and its one's complement,
 enabling the receiver to perform a simple error check. The `NEC` class supports
 these modes by checking the value of `addr` passed to `.transmit` and sending
 value is transmitted comprising the 8 bit address and its one's complement,
 enabling the receiver to perform a simple error check. The `NEC` class supports
 these modes by checking the value of `addr` passed to `.transmit` and sending

-the complement for 8 bit values.
+the complement for values < 256.

 
 

-`toggle` is ignored.
+A value passed in `toggle` is ignored.

 
 #### Sony classes
 
 
 #### Sony classes
 


@@ -119,17 +134,15 @@ Both send a `toggle` bit which remains constant if a button is held down, but
 changes when the button is released. The application should implement this
 behaviour, setting the `toggle` arg of `.transmit` to 0 or 1 as required.
 
 changes when the button is released. The application should implement this
 behaviour, setting the `toggle` arg of `.transmit` to 0 or 1 as required.
 

-# 4. Test results
+# 4. Principle of operation

 
 

-# 5. Principle of operation
-
-## 5.1 Pyboard
+## 4.1 Pyboard

 
 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. This is done by two methods of the base class, `.append` and `.add`. The
 
 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. This is done by two methods of the base class, `.append` and `.add`. The

-former takes a list of times (in μs) and appends them to the array. A bound
+former takes a list of times (in ) and appends them to the array. A bound

 variable `.carrier` keeps track of the notional on/off state of the carrier:
 this is required for bi-phase (manchester) codings.
 
 variable `.carrier` keeps track of the notional on/off state of the carrier:
 this is required for bi-phase (manchester) codings.
 


@@ -150,33 +163,17 @@ 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.
 
 next duration from the array. If it is not `STOP` it toggles the duty cycle
 and re-initialises T5 for the new duration.
 

-## 5.2 ESP32
-
-This is something of a hack because my drivers work with standard firmware.
-
-A much better solution will be possible when the `esp32.RMT` class supports the
-`carrier` option. A fork supporting this is
-[here](https://github.com/mattytrentini/micropython). You may want to adapt the
-base class to use this fork: it should be easy and would produce a solution
-capable of handling all protocols.
-
-A consequence of this hack is that timing is imprecise. In testing NEC
-protocols were reliable. Sony delivered some erroneous bitsreams but may be
-usable. Philips protocols require timing precision which is unachievable; these
-are unsupported and an exception will be thrown on an attempt to instantiate a
-Philips class on an ESP32.
+## 4.2 ESP32

 
 

-The ABC stores durations in Hz rather than in μs. This is because the `period`
-arg of `Timer.init` expects an integer number of ms. Passing a `freq` value
-enables slightly higher resolution timing. In practice timing lacks precision
-with the code having a hack which subtracts a nominal amount from each value to
-compensate for the typical level of overrun.
+The carrier is output continuously at the specified duty ratio. A pulse train
+generated by the RMT instance drives a hardware gate such that the IR LED is
+lit only when both carrier and RMT are high.

 
 

-The carrier is generated by PWM instance `.pwm` with its duty cycle controlled
-by software timer `._tim` in a similar way to the Pyboard Timer 5 described
-above. The ESP32 duty value is in range 0-1023 as against 0-100 on the Pyboard.
+The carrier is generated by PWM instance `.pwm` running continuously. The ABC
+constructor converts the 0-100 duty ratio specified by the subclass to the
+0-1023 range used by ESP32.

 
 

-# 6. References
+# 5. References

 
 [General information about IR](https://www.sbprojects.net/knowledge/ir/)
 
 
 [General information about IR](https://www.sbprojects.net/knowledge/ir/)