{"id":3224,"date":"2025-01-28T15:59:12","date_gmt":"2025-01-28T15:59:12","guid":{"rendered":"https:\/\/iotthinghub.com\/?p=3224"},"modified":"2025-01-28T17:25:17","modified_gmt":"2025-01-28T17:25:17","slug":"usb-real-time-sensor-data","status":"publish","type":"post","link":"https:\/\/iotthinghub.com\/?p=3224","title":{"rendered":"USB : Real Time Sensor Data"},"content":{"rendered":"\n

The Universal Serial Bus (USB) is technology that allows a person to connect an electronic device to a computer. It is a fast serial bus type. The STM32 performance line embeds a USB device peripheral compatible with the USB full-speed 12 Mb\/s. The USB interface implements a full-speed (12 Mbit\/s) function interface. It has software-configurable endpoint setting and suspend\/resume support. The USB peripheral implements an interface between a full-speed USB 2.0 bus and the APB bus. The clock source must use a HSE crystal oscillator.<\/p>\n\n\n\n

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Connection Diagram<\/p>\n<\/div>\n<\/div>\n\n\n\n

Not all STM32 has this USB feature. USB 2.0 version support 3 different speed i.e. low speed 1.5Mb\/s, full speed 12Mb\/s & high speed 480Mb\/s. Let\u2019s look at the different class of USB-<\/p>\n\n\n\n

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  • Audio Device: This class allows the implementation of audio devices such as headphones and microphones.<\/li>\n\n\n\n
  • Communication Device: This class allows the implementation of virtual COM ports and modems.<\/li>\n\n\n\n
  • Download Firmware Update (DFU): Device Firmware Upgrade (DFU) is a process of updating or replacing the firmware of a hardware device. Firmware is the low-level software embedded in hardware components that controls their functionality.<\/li>\n\n\n\n
  • Human Interface Devices (HID): This class allows the implementation of Human Interface devices allowing the interaction between a human and a machine such as game controllers, mouse, keyboards.<\/li>\n\n\n\n
  • Custom HID: A Custom HID (Human Interface Device) refers to a device that uses the USB HID protocol for communication but is designed for specific, custom purposes not covered by standard HID device types like keyboards, mice, or game controllers.<\/li>\n\n\n\n
  • Mass Storage Class: This class allows the implementation of mass storage devices ensuring data storage and exchange via USB.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n\n\n

    In this article we use USB Communication Device class for display real time sensor data to PC. Here we use simple sensor AHT20. AHT20, as a new generation of temperature and humidity sensors, has established a new standard in size and intelligence. Its uses communication protocol as I2<\/sup>C & is very simple to operate.<\/p>\n\n\n\n

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    The power supply range of AHT20 is 2.0-5.5V, and the recommended voltage is 3.3V. Please read the data sheet first. According to the data sheet the device has I2<\/sup>C address of 0x38. In order to read temperature & humidity only three step will need-<\/p>\n\n\n\n

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    In is tutorial we use STM32F103RCT6 microcontroller. I use I2C1 for OLED display purpose & I2C2 for AHT20 temperature & humidity measurement. You can use only 1 I2C protocol. Let\u2019s look at the code for interfacing which is very simple.<\/p>\n\n\n

    \n#define AHT20_ADD    0x38\n#define AHT20_INIT   0xBE\n#define AHT20_RESET  0xBA\n#define AHT20_TRIG   0xAC\nuint8_t Tx_Soft[1]={AHT20_RESET};\nuint8_t Tx_INIT[3]={AHT20_INIT,0x08,0x00};\nuint8_t Tx_Trig[3]={AHT20_TRIG,0x33,0x00};\nuint8_t Rx_Data[6];\nHAL_Delay(1000);\nHAL_I2C_Master_Transmit(&hi2c2,AHT20_ADD<<1,Tx_INIT,3,200);\nHAL_I2C_Master_Transmit(&hi2c2,AHT20_ADD<<1,Tx_Trig,3,200);\nHAL_Delay(100);\nHAL_I2C_Master_Receive(&hi2c2,(AHT20_ADD<<1|0x01),Rx_Data,6,200);\n<\/pre><\/div>\n\n\n
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    Here Rx_Data[6] represents the temperature & humidity data. Rx_Data[0] -> bit 7 represent measurement flag & bit 3 represent calibration flag.  Rx_Data[1], Rx_Data[2] & Rx_Data[3] -> upper 4 bits represent humidity. Rx_Data[4] -> lower 4 bits, Rx_Data[5] & Rx_Data[6] represents temperature. For calculation of<\/p>\n\n\n\n
    Temperature = (ST <\/sub>\/220<\/sup> )*200-50 Centigrade & Humidity = (SRH <\/sub>\/220<\/sup> )*100 % , 220 <\/sup>= 1048576<\/p>\n\n\n
    \nuint32_t Temperature,humidity;\nfloat tem,hum;\nhumidity=(Rx_Data[1]<<12)+(Rx_Data[2]<<4)+(Rx_Data[3]>>4);\nhum=(float)humidity\/1048576*100;\nTemperature=((Rx_Data[3]&0x0f)<<16)+(Rx_Data[4]<<8)+(Rx_Data[5]);\ntem=((float)Temperature\/1048576)*200-50;\n<\/pre><\/div>\n\n\n
    Here I use internal RTC feature for Real time weather forecasting. Here I use OLED for display purpose, if you don\u2019t want to display ignore OLED section. Let\u2019s initialize the RTC & use some string function for data transmitting to PC\/Laptop.<\/p>\n\n\n
    \nRTC_TimeTypeDef sTime;\nRTC_DateTypeDef sDate;  \nchar display_time[16],display_date[16], display_AHT20[16];\nchar Time_Zone[32],Weather_Data[32], PC_Monitor[64];\nchar *day_name[8]={"Sun","Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};\nHAL_RTC_GetTime(&hrtc,&sTime,RTC_FORMAT_BCD);\nHAL_RTC_GetDate(&hrtc,&sDate,RTC_FORMAT_BCD);\nsprintf(display_time," %02X:%02X:%02X ",sTime.Hours,sTime.Minutes,sTime.Seconds);\nsprintf(display_date," %02X\/%02X\/%02X %s",sDate.Date,sDate.Month,sDate.Year,day_name[sDate.WeekDay]);\nsprintf(Time_Zone,"%s Time %s",display_date,display_time);\nsprintf(Weather_Data,"Weather %02.2f C %02.2f %c HR",tem,hum,37);\nsprintf(PC_Monitor,"%s%s\\r",Time_Zone,Weather_Data);\n<\/pre><\/div>\n\n\n
    Our final step is to transfer the string to PC\/Laptop using STM32 USB Communication Device class. The code for USB Communication Device class-<\/p>\n\n\n
    \n#include "usbd_cdc_if.h"\nCDC_Transmit_FS(PC_Monitor, strlen(PC_Monitor));\n<\/pre><\/div>\n\n\n
    Data will send to PC without any external driver. Just Connect to PC\/laptop according to the block diagram below. In PC-> Device manager see the Virtual Port number & in Realterm connect according to the port number with any baud rate. For setting all parameter please follow the youtube tutorial. \u00a0<\/p>\n\n\n\n
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