Allwinner R128 chip application development case - ADC driving smoke sensor

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Allwinner R128 chip application development case - ADC driving smoke sensor [Copy link]

 

# ADC driven smoke sensor | Case code in this article | Download address | | ---------------------- | -------------------------------------- | | ADC driven smoke sensor case code | https://www.aw-ol.com/downloads?cat=24 | ## Principle introductionMQ-2 smoke sensor is a tin dioxide semiconductor gas-sensitive material, which is a surface ion N-type semiconductor. When it is at a temperature of 200 or 300°C, tin dioxide adsorbs oxygen in the air to form negative oxygen ions, which reduces the electron density in the semiconductor and increases its resistance. When in contact with smoke, if the potential barrier at the grain boundary is modulated by the smoke and changes, it will cause a change in the surface conductivity. This can be used to obtain information about the presence of this smoke. The greater the smoke concentration, the greater the conductivity and the lower the output resistance. MQ2 gas sensor can sensitively detect smoke, liquefied gas, butane, propane, methane, alcohol, hydrogen and other gases in the air. First, we build the circuit as follows:  | Pin | Button | | ---- | -------- | | PB0 | MQ2 AO pin | | GND | MQ2 GND | | 3V3 | MQ2 VCC | ## Loading scheme The development board we use is R128-Devkit, and we need to develop applications for the C906 core, so select `r128s2_module_c906` for the loading scheme ```bash $ source envsetup.sh $ lunch_rtos 1 ```  ## Check the GPADC driver `mrtos_menuconfig` Find the following drivers``` Drivers Options ---> soc related device drivers ---> GPADC devices ---> [*] enable gpadc driver [*] enable power protect driver ```  ## Write a program Open your favorite editor and modify the file: `lichee/rtos/projects/r128s2/module_c906/src/main.c`  ### Introduce header file ```c #include<sunxi_hal_gpadc.h> ```  Since the MQ2 is a heater-driven sensor, the sensor's calibration may drift if stored for a long time. When used for the first time after a long storage period, the sensor must be fully warmed up for 24-48 hours to ensure maximum accuracy. If the sensor has been used recently, it only takes 5-10 minutes to fully warm up. During the warm-up period, the sensor readings are usually high, and then gradually decrease until they stabilize. In order to implement the warm-up function, we first implement a `sleep` function to wait for the warm-up to complete before reading the ADC voltage value. ```c static inline int msleep(int ms) { vTaskDelay(ms / portTICK_RATE_MS); } ```  ## ADC function configuration#### GPADC initialization interface GPADC module initialization, mainly initializes the clock, interrupt and sampling rate configuration, etc. Here we initialize and check. ```c int hal_gpadc_init(void) ``` #### GPADC channel initialization Select and configure a GPADC channel, here configure and initialize channel 0. ```c hal_gpadc_channel_init(0); ``` #### GPADC read voltage interface reads the ADC voltage data of channel 0. ```c ret = gpadc_read_channel_data(0) ``` ### The complete code is as follows```c // Preheat module msleep(20000); // Initialize GPADC if(hal_gpadc_init() != 0){ printf("ADC Init failed!\n"); } // Initialize channel hal_gpadc_channel_init(0); // Read voltage while(1){ uint32_t vol_data = gpadc_read_channel_data(0); printf("channel 0 vol data is %u\n", vol_data); } // Release channel, not used here hal_gpadc_channel_exit(0); // Release GPADC, not used here hal_gpadc_deinit(); ``` ## Result After burning, you can see the output voltage value.  </sunxi_hal_gpadc.h>