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en:examples:digi:switch [2015/11/05 08:13] – heikopikner | en:examples:digi:switch [2020/07/20 09:00] (current) – external edit 127.0.0.1 | ||
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====== Switch ====== | ====== Switch ====== | ||
- | //Neccesary knowledge: [HW] [[en: | + | //Neccesary knowledge: |
+ | [HW] [[en: | ||
+ | [AVR] [[en: | ||
+ | [LIB] [[en: | ||
+ | [PRT] [[en: | ||
===== Theory ===== | ===== Theory ===== | ||
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- | ^ Push button switch ^ Toggle switch ^ Rocker | + | ^ Push button switch ^ Toggle switch ^ Rocker switch ^ |
- | |{{: | + | |{{: |
- | | {{: | + | | {{: |
+ | |||
+ | |||
+ | ^ Micro switch ^ DIL switch ^ | ||
+ | |{{: | ||
+ | | {{: | ||
In order to use a switch as a sensor connected to a microcontroller, | In order to use a switch as a sensor connected to a microcontroller, | ||
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| | ||
<code c> | <code c> | ||
- | // | ||
// Homelab User interface board button test code | // Homelab User interface board button test code | ||
- | // | ||
#include < | #include < | ||
- | // | ||
// Main program | // Main program | ||
- | // | ||
int main(void) | int main(void) | ||
{ | { | ||
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// Endless loop | // Endless loop | ||
- | while (true) | + | while (1) |
{ | { | ||
// green LED turns on when switch S1 is pressed | // green LED turns on when switch S1 is pressed | ||
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</ | </ | ||
- | ===== Practice ===== | + | ==== Filtration of switch bounce |
+ | [{{ : | ||
- | There are three push button-switches | + | Main method used for avoiding flickering caused by the bouncing of contacts is filtering. Filtering can be done electrically or by software. To filter electrically the switch must be connected through a low-pass filter – for example a RC filter – witch smoothed changes of voltage and therefore the pin of microcontroller does not have transient values. RC filter is shown on the drawing. Filtering by software is done by assessing |
- | The switches | + | Several software solutions |
- | Sample code for using buttons is based on the HomeLab pins library, | + | A program |
- | | ||
- | |||
- | |||
- | |||
- | |||
- | |||
- | ===== Filtration of switch bounce ===== | ||
- | |||
- | As mentioned in the introductory chapter of switches, there exists an issue of bouncing or flickering when dealing with mechanical switches. Problem arises since contacts are made of metal which has some elasticity, at the moment of connecting or disconnecting the contacts bounce and this results in number of false switching’s. The number and duration of the switching' | ||
- | |||
- | |||
- | [{{ : | ||
- | |||
- | Main method used for avoiding flickering caused by the bouncing of contacts is filtering. Filtering can be done electrically or by software. To filter electrically the switch must be connected through a low-pass filter – for example a RC filter – witch smoothed changes of voltage and therefore the pin of microcontroller does not have transient values. RC filter is shown on the drawing. Filtering by software is done by assessing the value of the pin where the switch is connected; if the value remains the same at number of times in pre set time limit, it is considered to have a steady position and hence has no flickering problem. However, with each type of filtering a delay factor in defining the status must be taken under consideration. | ||
- | |||
- | |||
===== Practice ===== | ===== Practice ===== | ||
- | Electrical filtering is not used on HomeLab switches, since it would not allow practicing the elimination of miss switching’s with software. The exercise is in two parts. The goal of the first part is to demonstrate the bouncing of User interface module switches. The following program is used for this; each pressing on the button will light the next LED in line. Wrongly pressed button will causes LEDs to light several times and it appears as the LEDs light randomly. | ||
- | <code c> | + | There are three push button-switches on the User interface |
- | // | + | |
- | // Homelab | + | |
- | // | + | |
- | #include < | + | |
- | // | + | Switch positions are shown in the hardware description. In order to read the status of the switches, the corresponding |
- | // Main program | + | |
- | // | + | |
- | int main(void) | + | |
- | { | + | |
- | int counter = 0; | + | |
- | + | ||
- | // Set LED pins as output and switch | + | |
- | pin_setup_output(led_red); | + | |
- | pin_setup_output(led_yellow); | + | |
- | pin_setup_output(led_green); | + | |
- | + | ||
- | pin_setup_input(S1); | + | |
- | // Endless loop | + | Below is a function for reading filtered values of a button for User interface module: |
- | while(1) | + | |
- | { | + | |
- | // Check if switch S1 is pressed | + | |
- | if(pin_get_value(S1) == 0) | + | |
- | { | + | |
- | // Light the corresponding LED | + | |
- | if(counter == 0) led_on(led_green); | + | |
- | else led_off(led_green); | + | |
- | if(counter == 1) led_on(led_yellow); | + | |
- | else led_off(led_yellow); | + | |
- | if(counter == 2) led_on(led_red); | + | |
- | else led_off(led_red); | + | |
- | + | ||
- | // Add counter and take a module | + | |
- | counter = (counter + 1) % 3; | + | |
- | + | ||
- | // Wait until switch is unpressed | + | |
- | while(pin_get_value(S1) == 0); | + | |
- | } | + | |
- | } | + | |
- | } | + | |
- | </ | + | |
- | + | ||
- | Several software solutions are used for filtering, this can be performed either easy or complex way both with its advantages and disadvantages. If the program is set to have only few infrequent pressings of the button, a long pause can be set to follow the pressing, this will rule out reaction to the switching caused by bounce. However, while using this solution must be considered – in case the user holds the button down for a long period of time, the program reacts also on the miss witching caused by the release of the button. A program which controls the state of the switch several times in fixed period of time is more dependable (the longer is the time and the higher is the number of controls performed, the better is the result). | + | |
<code c> | <code c> | ||
- | // | + | // Function for reading filtered values of a IO extension module |
- | // Function for reading filtered values of a IO extension module. | + | |
- | // | + | |
unsigned char button_read(pin button) | unsigned char button_read(pin button) | ||
{ | { | ||
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while (timeout-- > 0) | while (timeout-- > 0) | ||
{ | { | ||
- | // Having 8 place (bit) bufffer of state. | + | // Having 8 place (bit) bufffer of state |
// All previous states (bits) are shifted to left | // All previous states (bits) are shifted to left | ||
- | // and a new state(bit) is added to the right. | + | // and a new state(bit) is added to the right |
buffer <<= 1; | buffer <<= 1; | ||
buffer |= (pin_get_value(button) ? 0x01 : 0x00); | buffer |= (pin_get_value(button) ? 0x01 : 0x00); | ||
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} | } | ||
- | // If all 8 bits are low, then the button is definitely up. | + | // If all 8 bits are low, then the button is definitely up |
if (buffer == 0x00) | if (buffer == 0x00) | ||
{ | { | ||
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} | } | ||
- | // 1 ms break. | + | // 1 ms break |
- | // This function can be found from the library of the HomeLab. | + | // This function can be found from the library of the HomeLab |
_delay_ms(1); | _delay_ms(1); | ||
} | } | ||
- | + | // If can't examine the state, then assume that button was not pressed | |
- | // If can't examine the state, then assume that button was not pressed. | + | |
return 0; | return 0; | ||
} | } | ||
</ | </ | ||
- | This function generates a delay using a function which is explained in corresponding exercise. At this moment all we need to know about the delay function is that it generates a 1 ms delay at the end of each cycle for reading the state of the button. If the button is in the same position during 8 readings, it returns to the counted position. In case the button is unstable the entire procedure may take up to 100 ms. This function is included in the library of pins, hence there is no need to add it to the program for passing the example. | + | This function generates a delay using a function which is explained in corresponding exercise. At this moment all we need to know about the delay function is that it generates a 1 ms delay at the end of each cycle for reading the state of the button. If the button is in the same position during 8 readings, it returns to the counted position. In case the button is unstable the entire procedure may take up to 100 ms. This function is included in the library of pins, hence there is no need to add it to the program for passing the example. |
+ | |||
+ | The following example illustrates | ||
<code c> | <code c> | ||
- | // | + | // The program for filtering the debounce of buttons of User interface module |
- | // The program for filtering the debounce of buttons of User interface module. | + | |
- | // | + | |
#include < | #include < | ||
- | // | ||
// Main program | // Main program | ||
- | // | ||
int main(void) | int main(void) | ||
{ | { | ||
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// Wait until switch is unpressed | // Wait until switch is unpressed | ||
- | while(pin_get_value(S1) == 0); | + | while(button_read(S1) != 0); |
} | } | ||
} | } | ||
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<code c> | <code c> | ||
- | // Button demonstration example of User interface module. | + | // Button demonstration example of User interface module |
#include < | #include < | ||