How to test the IR sender beo4_tx_task()

[aanban]

Here I would like to share ideas for testing the transmit routine.

The frame consists of 455kHz bursts (about 200µs) followed by pauses. The length of the pause is determined by the pulse code, e.g. 3125µs for a BEO_ZERO. For the burst the ESP32 must generate a PWM signal with a 50% pulse/pause ratio and a frequency of 455kHz. During the pauses, the ratio is set to 0, then the output signal remains low.

The platformio IDE somehow does not support the newer Version. It's a shame that the espressif people let platformio down like this. To use the newer boards like ESP32-C6 and so on you have to switch to the pioarduino repository. The platformio.ini must explicitly refer to this platform, like so:

[env:esp32dev]
platform = https://github.com/pioarduino/platform-espressif32/releases/download/stable/platform-espressif32.zip
board = esp32dev
framework = arduino

;##### Serial Port Settings #####
monitor_filters = esp32_exception_decoder, log2file
monitor_speed   = 115200
;monitor_port    = COM4

;##### Upload-Port-Settings #####
upload_speed    = 921600
;upload_port     = COM4

;##### Build parameters #####
build_flags = 
  ;-DBOARD_HAS_PSRAM
  ;-mfix-esp32-psram-cache-issue
  ;-DCORE_DEBUG_LEVEL=5

;##### additional Libs #####
lib_deps = 
  https://github.com/knolleary/pubsubclient.git @ ^2.8.0
  https://github.com/bblanchon/ArduinoJson.git @ 7.3.0
  https://github.com/aanban/esp32_beo4

I will therefore rely on this platform and adapt the functions affected by the migration, e.g. ledcSetup() does not exist anymore and is included within ledcAttach(). And the channel is selected automatically.

old

    // setup the PMW and attach to IR transmit pin
    ledcSetup(beo4->m_tx_pwm,455000,4);  // pCarrier=455kHz,duty_range=[0..15]
    ledcAttachPin(beo4->m_tx_pin,beo4->m_tx_pwm); // attach to transmit pin
    ledcWrite(beo4->m_tx_pwm,0);         // duty=0 --> wake up with output=low

new

    constexpr uint32_t t_freq=455000;      ///< 455kHz carrier frequency
    constexpr uint32_t t_resolution=4;     ///< duty resolution (bits) --> range = [0..15] --> duty=8=50%

    // attach to pin, set carrier=455kHz and set resolution for duty-range=[0..15]
    ledcAttach(beo4->m_tx_pin,t_freq,t_resolution);  
    ledcWrite(beo4->m_tx_pin,0);  // duty=0 to start everything with output=low

example of BEO_SRC_AUDIO - BEO_CMD_RADIO frame

detail of 455kHz burst

[aanban]

The investigations were continued. A setup with a TSAL6200 IR emitting diode and an NPN transistor was not satisfactory. The loose wiring on the breadboard also resulted in poor signal quality, so I now soldered this circuit onto a hole pattern board.

The control of the diodes now works well, but I found that the 200µs burst was sometimes too long, and the pauses were also not consistent. Further attempts were made by replacing the one-shot-timer mimic with delayMicroseconds() pauses. I also blocked the interrupts using critical sections for the duration of the transmission. And last but not least, I found an error when extracting the data bits. Of course, they have to be read out in the opposite direction.

Code-Snippet from beo4_tx_task() showing the taskENTER_CRITICAL(), and shifting beoCode in oposite direction

    for(;;) {  // wait until beoCodes arrive at queue
      if(pdTRUE != xQueueReceive(beo4->m_beo4_tx_queue,&beoCode,portMAX_DELAY)) { 
        ets_printf("TaskBeoTx().xQueueReceive() failed ");  
        continue;
      }
      // generate carrier pulses and pauses according to beoCode
      taskENTER_CRITICAL(&my_spinlock);
      beo4->tx_pc(bZero);        // send start sequence: 1,1,5
      beo4->tx_pc(bZero);
      beo4->tx_pc(bStart);
      beo4->tx_pc(bZero);        // send beoLink (always bZero)
      curBit=preBit=0;           // init current and previous Bit
      for(jc=15,ic=0;ic<16;ic++,jc--) {     // generate 16 data bits of BeoCode
        uint8_t pulseCode=0;
        curBit=(beoCode>>jc) & 1;
        if(curBit==preBit) pulseCode=bSame;
        else if(1==curBit) pulseCode=bOne;
        else               pulseCode=bZero;
        preBit=curBit;
        beo4->tx_pc(pulseCode);  // send pulsecode for current Bit
      }
      beo4->tx_pc(bStop);        // send stop code
      beo4->tx_pc(0);            // finish frame with final carrier pulse
      taskEXIT_CRITICAL(&my_spinlock);
    }

unsing delayMicroseconds() instead of one-shot-timers

    inline void tx_pc(uint8_t pulsecode) { 
      uint32_t pulse_width=(uint32_t)(((uint64_t)pulsecode*t_pc)-t_low_pulse);
      ledcWrite(m_tx_pin,8); // turn carrier on
      delayMicroseconds(200);
      ledcWrite(m_tx_pin,0); // turn carrier off
      if(0 < pulsecode) {    // no timer for the final carrier-pulse
        delayMicroseconds(pulse_width);
      }
    }

--> See commit ec979dc

I was able to successfully send from one ESP32 + TSAL6200 and receive with a second ESP32+TSO7000. I will provide the sources for the two main.cpp.

[aanban]

A further investigation and simulation with LTSPICE. Darlington transistors are more suitable than the BS170 mosfets from above. The 25 year old BeoCenter 2500 was able to receive various IR frames. IR-Leds with 880nm wavelength fit better to B&O systems. The current transmitting circuit consists of a TIP121 and TSHA6200 IR diodes.

The range of the transmitting diodes can certainly be increased even further. This original circuit from B&O will probably fit best. This is also a Darlington circuit with discreet transistors, each driving only one IR diode, and a very small resistor (0.82 Ohm). The forward current will then be approx. 1A.

[aanban]

My current circuit works with two TSHA6500 IR transmitter diodes, each driven by a own TIP121 darlington transistor.It is also possible to place the transmitter at the other end of the room (approx. 7m) and the BeoSystem 2500 responds reliably.

edit: grammar