8.1. ADC - Key Detection Voltage

This demo mainly introduces the key functions of the ADC. The ADC is used to detect the voltage value of the key input pin and judge whether the corresponding key is pressed according to different voltage divisions.

8.1.1. Hardware Connection

This demo is based on BL706_AVB:

   GPIO function         GPIO pin
----------------------------------
    ADC CH8      <-->     GPIO18

Voltage divider circuit:

adc key

8.1.2. Software Implementation

  • For the code see examples/adc/adc_key

1#define BSP_ADC_CLOCK_SOURCE  ROOT_CLOCK_SOURCE_XCLK
2#define BSP_ADC_CLOCK_DIV  0

  • Configure the ADC device clock source, see bsp/board/bl706_avb/clock_config.h

1#define CONFIG_GPIO18_FUNC GPIO_FUN_ADC

  • Configure ADC device multiplexing pins, see bsp/board/bl706_avb/pinmux_config.h

 1#define BSP_USING_ADC0
 2
 3#if defined(BSP_USING_ADC0)
 4#ifndef ADC0_CONFIG
 5#define ADC0_CONFIG \
 6{   \
 7    .clk_div = ADC_CLOCK_DIV_32,\
 8    .vref = ADC_VREF_3P2V,\
 9    .continuous_conv_mode = DISABLE,\
10    .differential_mode = DISABLE,\
11    .data_width = ADC_DATA_WIDTH_16B_WITH_256_AVERAGE,\
12    .fifo_threshold = ADC_FIFO_THRESHOLD_1BYTE,\
13    .gain = ADC_GAIN_1\
14}
15#endif
16#endif

  • Enable BSP_USING_ADC0 and configure the ADC device, see bsp/board/bl706_iot/peripheral_config.h

 1adc_channel_cfg_t adc_channel_cfg;
 2adc_channel_cfg.pos_channel = posChList;
 3adc_channel_cfg.neg_channel = negChList;
 4
 5adc_register(ADC0_INDEX, "adc_key", DEVICE_OFLAG_STREAM_RX);
 6
 7adc_key = device_find("adc_key");
 8
 9if(adc_key)
10{
11    ADC_DEV(adc_key)->continuous_conv_mode = ENABLE;
12    device_open(adc_key, DEVICE_OFLAG_STREAM_RX);
13    device_control(adc_key,DEVICE_CTRL_ADC_CHANNEL_CONFIG,&adc_channel_cfg);
14
15}else{
16    MSG("device open failed\r\n");
17}
18
19adc_channel_start(adc_key);

  • First call the adc_register function to register the adc_key device, which is currently registered as ADC0

  • Then use the find function to find the handle corresponding to the device and save it in the adc_key handle

  • Then use device_open to open the adc_key device in polling mode, and call device_control to complete the ADC related configuration

  • Finally call adc_channel_start to enable ADC conversion

1device_read(adc_key,0,(void *)&result_val,1);
2keyValue = get_adc_key_value(result_val.volt * 1000);
3if( keyValue!=KEY_NO_VALUE){
4
5    MSG("key %d pressed\r\n",keyValue);
6    MSG("result_val.volt: %0.2f mv\n", (result_val.volt * 1000));
7}

  • Call device_read to read the adc_key device information and save it to the result_val structure

  • Call the get_adc_key_value function to get the current key value and voltage value

8.1.3. Compile and Program

1 $ cd <sdk_path>/bl_mcu_sdk
2 $ make BOARD=bl706_avb APP=adc_key

8.1.4. Experimental Phenomena

In this experiment, pressing SW1 ~ SW5 on the board in turn will get different voltage values:

  • key 0: ~0V

  • key 1: ~0.1V

  • key 2: ~0.2V

  • key 3: ~0.3V

  • key 4: ~0.43V

operation result:

../../../_images/adc_key_result.png

Video display: