View source for Experiment 26: MQ-2 Smoke Sensor Experiment

*[[Basic Experiment Kits For Arduino]]
*[[Basic Experiment Kits For Raspberry Pi]]
== Arduino ==
=== Experimental Phenomenon ===
* Print data collected by the module through the serial port.

=== Notes ===
*After powering on, wait for 1 minute for preheating before measurement. After preheating, you can feel significant heat from the probe.

=== Circuit Connection ===
* [[File:实验二十六：MQ-2烟雾传感器实验_接线.png|800px]]

=== Reference Program ===
<pre>
void setup()
{
  Serial.begin(9600); //Set serial baud rate to 9600 bps
}
void loop()
{
  int val;
  val=analogRead(0);//Read Gas value from analog 0
  Serial.println(val,DEC);//Print the value to serial port
  delay(100);
}
</pre>

== Raspberry Pi ==
=== Circuit Connection ===
*[[File:实验二十六：MQ-2烟雾传感器实验_接线1.png|800px]]

=== Program Execution ===
==== Python ====
* Install the gpiozero library
**You can use the following command to install the library:
<pre>
sudo apt update
sudo apt install python3-gpiozero
</pre>
:*For other systems on the Raspberry Pi, you can use the following command to install the library:
<pre>
sudo pip3 install gpiozero
</pre>
:*Run the following command to view the GPIO pin definitions on the Raspberry Pi:
<pre>
pinout
</pre>
*Enable the SPI interface
<pre>
sudo raspi-config
Select Interfaces oOptions -> SPI -> “Would you like the SPI interface to be enabled? ”Select Yes -> “The SPI interface is enabled” Select Yes -> Select finish
</pre>
*Shut down the Raspberry Pi. With the power off, connect the corresponding modules to the circuit according to the provided circuit connection, and then start the Raspberry Pi.
*Download the Raspberry Pi reference example, unzip the file, copy it to the user directory, and run it:
<pre>
cd raspberrypi/26/python_gpiozero
python sensor.py
</pre>
*You can see the Raspberry Pi running the program correctly. To exit, press ctrl+C.
*Instruction Description: '''gpiozero.Button(pin, pull_up, active_state, bounce_time, hold_time, hold_repeat)'''
** Button inherits from DigitalInputDevice and represents a simple button or switch. One end of the button is connected to the ground, and the other end is connected to any GPIO pin; alternatively, one end of the button is connected to the 3V3 pin, and the other end is connected to any GPIO pin. Then, set pull_up to False in the Button's initialization method.
** Main Parameters:
*** pin: GPIO pin number;
*** pull_up: Internal pull-up/pull-down resistor setting,
**** When set to True (default), the GPIO pin is pulled high, and the other end of the button should be connected to ground.
**** When set to False, the GPIO pin is pulled low, and the other end of the button should be connected to 3V3.
**** When set to None, the GPIO pin is floating, and gpiozero cannot guess the active state; you must set active_state.
*** active_state:
**** When set to True, the software considers the pin state as "high" when the hardware pin state is "high".
**** When set to False, the input polarity is reversed; when the hardware pin state is "high", the software considers the pin state as "low".
**** Use this parameter to set the unknown pin active state when pull_up is set to None.
**** When pull_up is set to True or False, the pin's active state is automatically assigned.
*** bounce_time: Software debounce time. Generally, a switch has unstable signals within about 20ms, known as "switch bounce".
**** When set to None, no software debounce compensation is performed; otherwise, this parameter is the length of time (in seconds) that the component ignores after an initial change, with a default of 1s.
*** hold_time: The time after pressing the button until when_held is triggered, in seconds.
*** hold_repeat:
**** If True, when_held will continue to be triggered every hold_time interval as long as the button remains pressed.
**** If False, when_held will only trigger once.

*For more commands, please refer to the [https://gpiozero.readthedocs.io/en/latest/installing.html gpiozero documentation]

== Example Download ==
* [[:File:Basic Experiment Kits For Arduino.zip|Arduino Example Programs]]
* [[:File:Basic Experiment Kits For Raspberry Pi.zip|Raspberry Pi 5 Example Programs in Python]]

== Related Examples ==
{{Arduino and Raspberry Pi Case}}