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en:iot-open:practical:hardware:sut:stm32:emb10_1 [2024/04/10 17:22] – created ktokarzen:iot-open:practical:hardware:sut:stm32:emb10_1 [2024/04/10 19:09] (current) – [EMB10: Controlling standard servo] ktokarz
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-====== EMB10: Controlling standard servo ====== +====== STM_10: Controlling standard servo ====== 
-You will learn how to control a standard miniature servo with the STM32 System on Chip. Standard miniature analogue servo is controlled with a PWM signal of frequency 50Hz with a duty cycle period between 1 ms (rotate to 0) and 2 ms (rotate to 180 degrees), where 1.5 ms corresponds to 90 degrees. +You will learn how to control a standard miniature servo with the STM32 System on Chip. Standard miniature analogue servo is controlled with a PWM signal of frequency 50Hz with a duty cycle period between 1 ms (rotate to 0) and 2 ms (rotate to 180 degrees), where 1.5 ms corresponds to 90 degrees. Some servos have other duty cycle minimum and maximum values, always refer to the documentation.
 <note warning>Do not keep the servo rotating when leaving the lab. Implement your code as non-repeating. A servo that remains rotating for a long time may easily wear out its gears, overheat and even burn!</note> <note warning>Do not keep the servo rotating when leaving the lab. Implement your code as non-repeating. A servo that remains rotating for a long time may easily wear out its gears, overheat and even burn!</note>
 A servo has a red arrow presenting the gauge's current position. <note important>Note that servos tend to have relatively high implementation inaccuracy. Moreover, as the arrow is not in the centre of view of the camera but instead to the corner, the reading may be subject to error because of the parallaxes and lens distortion.</note>  A servo has a red arrow presenting the gauge's current position. <note important>Note that servos tend to have relatively high implementation inaccuracy. Moreover, as the arrow is not in the centre of view of the camera but instead to the corner, the reading may be subject to error because of the parallaxes and lens distortion.</note> 
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 The servo is an example of a physical actuator. It requires some time to operate and change the position. Please give it time to set a new position between consecutive changes of the control PWM signal. Moreover, because of the observation via camera, too quick rotation may not be observable at all depending on the video stream fps. A gap of 2s between consecutive rotations is usually a reasonable choice. The servo is an example of a physical actuator. It requires some time to operate and change the position. Please give it time to set a new position between consecutive changes of the control PWM signal. Moreover, because of the observation via camera, too quick rotation may not be observable at all depending on the video stream fps. A gap of 2s between consecutive rotations is usually a reasonable choice.
 ===== Prerequisites ===== ===== Prerequisites =====
-To ease servo control, instead of use of ''ledc'' we will use a dedicated library: +A good understanding of the PWM signal and duty cycle is necessary. In this scenario, we use built-in timers to control the PWM hardware channels of the STM32WB55 chip. In this case, we do not use any external library; instead, we use the hardware timer library built in the Arduino Core STM32 framework for STM32WB55 (stm32duino)(("stm32duino", https://github.com/stm32duino)) so that no additional external libraries will be included in the project. 
-<code bash> +\\ 
-ib_deps = dlloydev/ESP32 ESP32S2 AnalogWrite@^5.0.2 +Some servos tend to go below 1 ms and above 2 ms to achieve a full 180-degree rotation range. For example, the servo in our laboratory (MG90/SG90) accepts values starting from 500 ms, and ending at 2500 ms. If there is a need for a high accuracy of rotation, it is possible to fine-tune the minimum and maximum duty cycle values.
-</code> +
-This library requires minimum setup but, on the other hand, supports, i.e. fine-tuning of the minimum and maximum duty cycle as some servos tend to go beyond 1ms and above 2ms to achieve a full 180-degree rotation range. It is usually provided in the technical documentation accompanying the servo.+
  
 ===== Suggested Readings and Knowledge Resources ===== ===== Suggested Readings and Knowledge Resources =====
   * [[en:iot-open:introductiontoembeddedprogramming2:cppfundamentals]]   * [[en:iot-open:introductiontoembeddedprogramming2:cppfundamentals]]
-  * [[en:iot-open:hardware2:esp32|]] +  * [[en:iot-open:hardware2:stm32]]
-  * [[en:iot-open:practical:hardware:sut:esp32|]] +
-  * [[en:iot-open:embeddedcommunicationprotocols2:pwm|]]+
   * [[en:iot-open:hardware2:actuators_motors|]]   * [[en:iot-open:hardware2:actuators_motors|]]
 +  * [[en:iot-open:practical:hardware:sut:stm32|]]
 +  * [[en:iot-open:embeddedcommunicationprotocols2:pwm|]]
 ===== Hands-on Lab Scenario ===== ===== Hands-on Lab Scenario =====
  
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 ==== Start ==== ==== Start ====
-Check if the servo is in the camera view. The servo is controlled with GPIO 37.+In the laboratory equipment, the servo and the fan are connected to the same hardware timer instance. It means that both elements use the same base frequency of the PWM signal. If you use a fan and servo in the same project the frequency of the PMW signal needs to match the servo requirements. 
 +\\ 
 +The hardware timer library implements functions which allow us to control the duty cycle of the PWM signal and express it in different formats, including percentages. In the case of setting the PWM duty cycle expressed in percentages, the minimum value is 0, and the maximum is 100. We can also express the duty cycle in microseconds which is easier to calculate for the servo.
  
 ==== Steps ==== ==== Steps ====
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 <note warning>Do not keep the servo rotating when leaving the lab. Implement your code as non-repeating. A servo that remains rotating for a long time may easily wear out its gears, overheat and even burn!</note> <note warning>Do not keep the servo rotating when leaving the lab. Implement your code as non-repeating. A servo that remains rotating for a long time may easily wear out its gears, overheat and even burn!</note>
 === Step 1 === === Step 1 ===
-Include servo control library, specific for ESP32 and declare GPIO, minimum and maximum duty cycle values:+Include Arduino and timer libraries, specific to STM32. The servo is controlled with GPIO PA_10 (the PA_10 name is the STM Nucleo naming convention). Define the pin name constant.
 <code c> <code c>
-#include <Servo.h> +#include "Arduino.h" 
-#define SRV_PIN 37+#include <HardwareTimer.h> 
 +#define SERVO_PWM_PIN PA0
 </code> </code>
-MG 90 servos that we use in our lab are specific. As mentioned above, to achieve a full 180-degree rotation range, their minimum and maximum duty cycle timings go far beyond standards. Here, we declare minimum and maximum values for the duty cycle (in microseconds) and a PWM control channel (2):+ 
 +We will also need some variables:
 <code c> <code c>
-#define PWMSRV_Ch     2 +// PWM variables definitions 
-#define srv_min_us  550 +TIM_TypeDef *SRVInstance;        //General hardware instance 
-#define srv_max_us 2400+uint32_t channelSRV;             //2 channel for the servo 
 +HardwareTimer *MyTimServo;       //Hardware Timer class for Servo PWM
 </code> </code>
  
 === Step 2 === === Step 2 ===
-Define a servo controller object:+The hardware timer library uses internal timer modules and allows us to define channels attached to the timer. Channels represent the output pins connected to the hardware elements. Our laboratory board uses the same timer to control the servo and fan. In this example, we will use one channel for the servo only setting the proper PWM frequency of the timer. The channel connected to the servo controls the PWM duty cycle. 
 + 
 +Create the timer instance type based on the servo pin: 
 <code c> <code c>
-static Servo srv;+TIM_TypeDef *SRVInstance = (TIM_TypeDef *)pinmap_peripheral(digitalPinToPinName(SERVO_PWM_PIN), PinMap_PWM);
 </code> </code>
 +<note>
 +The same timer is used for the fan in the scenario STM_1A.
 +</note>
  
-=== Step 3 === +Define the channel for servo:
-Initialise parameters (duty cycle, channel, GPIO):+
 <code c> <code c>
-srv.attach(SRV_PIN, PWMSRV_Ch,srv_min_us, srv_max_us);+channelSRV = STM_PIN_CHANNEL(pinmap_function(digitalPinToPinName(SERVO_PWM_PIN), PinMap_PWM));
 </code> </code>
-50Hz frequency is standard, so we do not need to configure it. 
  
 +Instantiate HardwareTimer object. Thanks to 'new' instantiation, HardwareTimer is not destructed when setup() function is finished.
 +<code c>
 +MyTimServo = new HardwareTimer(SRVInstance);
 +</code>
 +
 +Configure and start PWM
 +<code c>
 +MyTimServo->setPWM(channelSRV, SERVO_PWM_PIN, 50, 5); // 50 Hertz, 5% dutycycle.
 +</code>
 +
 +=== Step 3 ===
 +MG 90 servos that we use in our lab are specific. As mentioned above, to achieve a full 180-degree rotation range, their minimum and maximum duty cycle timings go far beyond standards. We will create a function for calculating the duty cycle for the servo with the angle as the input parameter.
 +
 +<code c>
 +void fSrvSet(int pAngle)
 +{
 +  if (pAngle<0) pAngle=0;        //check boudaries of angle
 +  if (pAngle>180) pAngle=180;
 +  int i_srv=500+(200*pAngle)/18; //minimal duty cycle is 0,5ms, maximal 2,5ms
 +  MyTimServo->setCaptureCompare(channelSRV, i_srv, MICROSEC_COMPARE_FORMAT);  //modify duty cycle
 +};
 +</code>
 === Step 4 === === Step 4 ===
-Rotating a servo is as easy as writing the desired angle to the controller class, e.g.:+Rotating a servo is as easy as calling our function with the desired angle as the parameter, e.g.:
 <code c> <code c>
-srv.write(SRV_PIN,180);+fSrvSet(90);
 delay(2000); delay(2000);
 </code> </code>
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 **How do I know minimum and maximum values for the timings for servo operation?**: Those parameters are provided along with servo technical documentation, so you should refer to them. Our configuration reflects the servos we use (MG90/SG90), and as you can see, it goes far beyond the standard servo rotation control that is a minimum of 1000us and a maximum of 2000us. Using standard configuration, your servo won't rotate at full 180 degrees but at a shorter rotation range. **How do I know minimum and maximum values for the timings for servo operation?**: Those parameters are provided along with servo technical documentation, so you should refer to them. Our configuration reflects the servos we use (MG90/SG90), and as you can see, it goes far beyond the standard servo rotation control that is a minimum of 1000us and a maximum of 2000us. Using standard configuration, your servo won't rotate at full 180 degrees but at a shorter rotation range.
 +**Would it be possible to control the servo and fan with the same program?**: Yes, but you have to remember that servo has very strict timing requirements. Because both elements share the same timer, they also share the same frequency which must be set according to the servo requirements.
  
 ==== Result validation ==== ==== Result validation ====
en/iot-open/practical/hardware/sut/stm32/emb10_1.1712769764.txt.gz · Last modified: 2024/04/10 17:22 by ktokarz
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