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| en:iot-open:practical:hardware:sut:esp32:emb1a_1 [2024/03/22 10:01] – [Project information] pczekalski | en:iot-open:practical:hardware:sut:esp32:emb1a_1 [2024/04/09 12:55] (current) – [FAQ] pczekalski |
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| ==== Steps ==== | ==== Steps ==== |
| To use PWM in ESP32, it is best to use built-in ''ledc*'' functions [[https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/peripherals/ledc.html|LEDC documentation on the ESP32 manufacturer's page]]. | To use PWM in ESP32, it is best to use built-in ''ledc*'' functions [[https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/peripherals/ledc.html|LEDC documentation on the ESP32 manufacturer's page]]. |
| The ''leds'' use timers and have channels attached to the timer. We will use one channel numbered 0. The channel controls the PWM duty cycle. Do not be mislead with the use of the ''leds'' functions: they generate PWM signal and it is meaningless either you control a LED, bulb or a fan (as here). | The "leds" use timers and have channels attached to the timer. We will use one channel numbered 0. The channel controls the PWM duty cycle. Do not be misled by the "leds" functions: they generate a PWM signal, and it is meaningless whether you control an LED, bulb, or fan (as here). |
| === Step 1 === | === Step 1 === |
| Define some parameters, including channel numbers, PWM resolution (here 8-bit) and PWM frequency (1000Hz): | Define some parameters, including channel numbers, PWM resolution (here 8-bit) and PWM frequency (1000Hz): |
| |
| === Step 2 === | === Step 2 === |
| Initialise 3 channels for PWM and make them dark: | Initialise fan PWM channel and make it to stop (duty cycle 0): |
| <code c> | <code c> |
| ledcSetup(fanPWMChannel, fanPWMFrequency, fanPWMResolution); | ledcSetup(FAN_PWM_Ch, FAN_PWM_FREQ, FAN_PWM_RESOLUTION); //Initialise channel |
| ledcAttachPin(fanPWMPin, fanPWMChannel); | ledcAttachPin(FAN_PIN, FAN_PWM_Ch); //Bind it to the PWM |
| delay(100); | delay(100); |
| ledcWrite(fanPWMChannel,0); | ledcWrite(FAN_PWM_Ch,0); //Write to CHANNEL, not to PIN! |
| </code> | </code> |
| To control the fan rotation speed (via PWM), use ''ledcWrite(PWM_Channel, duty_cycle_value);''. | |
| === Step 3 === | === Step 3 === |
| | To control the fan rotation speed (via PWM), use ''ledcWrite(FAN_PWM_Ch, duty_cycle_value);''.\\ |
| | <note tip>Note you write to **channel**, not to the **pin**!\\ |
| | A common source code mistake causes the fan not to operate correctly.</note> |
| | A ''ledcWrite'' with a ''duty_cycle_value'' equal to 0 causes the fan to stop.\\ |
| | The maximum ''duty_cycle_value'' is determined by the ''FAN_PWM_RESOLUTION'', which is 8-bit in our case, so maximum is 255. In that case, the fan operates at full speed. |
| |
| <note>There is a number of handy functions in the ''ledc'' library, including (among others): | <note>There is a number of handy functions in the ''ledc'' library, including (among others): |
| **The fan rotates itself. Why?**: It is connected via the MOS FET transistor that tends to saturate when the GPIO (35) is not controlling it. So, to ensure the fan is stopped, bind a PWM channel to it and force the duty cycle set to 0. | **The fan rotates itself. Why?**: It is connected via the MOS FET transistor that tends to saturate when the GPIO (35) is not controlling it. So, to ensure the fan is stopped, bind a PWM channel to it and force the duty cycle set to 0. |
| |
| **The fan is not rotating?**: Besides possible configuration and programming errors, it is essential to understand that setting duty cycle, e.g. to 1, won't start spinning: a minimum value (a threshold) causes rotation. Moreover, the relation between rotation speed, air pressure and duty cycle controlling the fan is not linear. | **The fan is not rotating?**: Besides possible configuration and programming errors, it is essential to understand that setting duty cycle, e.g. to 1, won't start spinning: a minimum value (a threshold) causes rotation. Moreover, the relation between rotation speed, air pressure and duty cycle controlling the fan is not linear. You may also be a victim of the common coding mistake of using a GPIO number instead of the channel number (first parameter) in the ''ledcWrite'' function: use the PWM channel number! |
| \\ | \\ |
| **What is the maximum number of channels?**: the MCU we use here is ESP32-S3, so it has 8 PWM channels. You can use timers and software implementation of the PWM signal if you need more, but that is a bit tricky and may not be as precise as hardware PWM implementation. | **What is the maximum number of channels?**: the MCU we use here is ESP32-S3, so it has 8 PWM channels. You can use timers and software implementation of the PWM signal if you need more, but that is a bit tricky and may not be as precise as hardware PWM implementation. |
