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EMB1A: Use of RGB LEDs
This scenario presents how to handle the rotation speed of the fan. It is done using a PWM signal, as presented in this tutorial. The fan pumps the air into the yellow pressure chamber with a pressure sensor inside. Because it is pretty hard to monitor rotation speed with the camera, this scenario should be run along with scenario following scenario EMB1B: Reading environmental data with a Bosch integrated sensor that will indirectly measure rotation speed using pressure changes.
Prerequisites
A good understanding of the PWM signal and duty cycle is necessary. We also use built-in timers to control the PWM hardware channels of the ESP32 chip. In this case, we do not use an external library; instead, we use built-in tools in the Arduino framework for ESP32 so that no additional libraries will be included in the project.
Suggested Readings and Knowledge Resources
Hands-on Lab Scenario
Task to be implemented
Implement a program that will spin the fan using a PWM signal.
Execute your experiment once, e.g. in the
setup() function, but not infinitely, in the loop(). We appreciate letting you keep your fan off when finishing your experiments. They are very noisy, and our servers love silence!
Start
Assuming you will use 8-bit PWM resolution, the minimum value is 0, and the max (full speed) is 255.
Steps
To use PWM in ESP32, it is best to use built-in ledc* functions 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).
Step 1
Define some parameters, including channel numbers, PWM resolution (here 8-bit) and PWM frequency (1000Hz):
#define FAN_PIN 35 #define FAN_PWM_Ch 0 #define FAN_PWM_FREQ 1000 #define FAN_PWM_RESOLUTION 8
GPIO pins controlling the fan is 35.
Step 2
Initialise 3 channels for PWM and make them dark:
ledcSetup(fanPWMChannel, fanPWMFrequency, fanPWMResolution); ledcAttachPin(fanPWMPin, fanPWMChannel); delay(100); ledcWrite(fanPWMChannel,0);
To control the fan rotation speed (via PWM), use ledcWrite(PWM_Channel, duty_cycle_value);.
Step 3
There is a number of handy functions in the
ledc library, including (among others):analogWrite(pin,value);to keep compatibility with genuine Arduino,ledcFade(pin, start_dutycycle, end_dutycycle, fade_time_ms);that you can use instead of the loop to slow down rotation gently,ledcDetach(pin);to detach a pin from the channel (and thus release the PWM channel),ledcWriteNote(pin, note, octave);wherenoteis one of the values: NOTE_C, NOTE_Cs, … (and so on, music notes, up to NOTE_B) - it is useful when PWM controls a speaker, to generate a perfect musical note, but we do not use speakers here, sorry.
Result validation
You can observe rotation change by measuring air pressure in the chamber only. To distinguish whether the fan is stopped or rotating, you can observe it via the video stream.
FAQ
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.
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 bit resolution for PWM?: it is between 1 and 14 bits in this particular MCU.
What PWM frequency should I use?: there is no straightforward answer to this question, but setting too low a frequency will cause the inability to control the fan: 1000Hz (1kHz) seems reasonable and has been tested with this configuration.
Project information
This Intellectual Output was implemented under the Erasmus+ KA2.
Project IOT-OPEN.EU Reloaded – Education-based strengthening of the European universities, companies and labour force in the global IoT market.
Project number: 2022-1-PL01-KA220-HED-000085090.
Erasmus+ Disclaimer
This project has been funded with support from the European Commission.
This publication reflects the views of only the author, and the Commission cannot be held responsible for any use that may be made of the information contained therein.
Copyright Notice
This content was created by the IOT-OPEN.EU Reloaded consortium, 2022,2024.
The content is Copyrighted and distributed under CC BY-NC Creative Commons Licence, free for Non-Commercial use.
