ADC is a hardware device that converts continuously changing analog signals to discrete digital signals such as temperature, pressure, sound, or images signals, etc. Digital signals are easier to be stored, processed, and transmitted.
This can be achieved by using an analog-to-digital converter device and it is widely used in various platforms. According to history, ADC was first used to convert wireless signals to digital signals, for example, television signals, or signals from long-short broadcast stations.
An ADC (analog-to-digital converter) is a hardware device that converts continuously changing analog signals to discrete digital signals. Usually, these analog signals include temperature, pressure, sound, video and many other types of signals. Converting them is important, as digital signals are easier to store, process, and transmit. This conversion can be achieved by using an ADC device which is commonly integrated in various platforms. Historically, ADCs were first used to convert received wireless signals to digital signals, for example, television signals, or signals from long-short broadcast stations.
### Conversion Process
As shown in the figure below, the analog-to-digital conversion generally involves steps of sampling, holding, quantifying, and encoding. In actual circuits, some processes are combined, such as sampling and holding, and quantization and encoding are implemented simultaneously in the conversion process.
As shown in the figure below, the analog-to-digital conversion generally involves steps of sampling, holding, quantifying, and encoding. In actual circuits, some processes are combined, such as sampling and holding, while quantization and encoding are implemented simultaneously in the conversion process.
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@@ -17,15 +16,15 @@ The process of converting a numerically continuous analog quantity into a digita
### Resolution
Resolution is represented as binary (or decimal) numbers. Generally, it comes with 8 bits, 12 bits, 16 bits, etc. Higher bits means higher resolution, thus, more accuracy in conversion of analog to digital signals.
Resolution is represented as binary (or decimal) numbers. Generally, it comes in 8 bits, 10 bits, 12 bits, 16 bits, etc. A larger resolution, in bits, means more accuracy in the conversion of analog to digital signals.
### Precision
Precision means maximum error values between analog signals and real ADC device numerical points’ values.The deviation is measured from the output values to the liner maximum values. However, precision and resolution are used for different purposes and different concepts.
Precision is the maximum error value between analog signals and real ADC device numerical points’ values.An ADC with a high resolution might have a low precision, meaning that factors like noise can affect the numerical ADC reading more than small changes in the input signal.
### Conversion Rate
The conversion rate is the reciprocal of time taken for an ADC device to complete conversion from analog to digital signals. For example, an ADC device with a conversion rate of 1MHz means ADC conversion time is 1 microsecond.
The conversion rate is the reciprocal of time taken for an ADC device to complete conversion from an analog to a digital signal. For example, an ADC device with a conversion rate of 1MHz means that the ADC conversion time is 1 microsecond.
## Access ADC Device
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@@ -40,7 +39,7 @@ The application accesses the ADC hardware through the ADC device management inte
### Find ADC Devices
The application gets the device handler based on the ADC device name to operate the ADC device. Following is the interface function to find the devices,
The application gets the device handler based on the ADC device name to operate the ADC device. Following is the interface function to find the devices:
@@ -129,9 +129,9 @@ rt_kprintf("the voltage is :%d.%02d \n", vol / 100, vol % 100);
The calculation formula of the actual voltage value is: `sampling value * reference voltage/(1 << resolution digit)`. In the above example, variable *vol* was enlarged 100 times, so finally the integer part of voltage is obtained through *vol / 100*, and the decimal part of voltage is obtained through *vol % 100*.
### Close the ADC Channel
### Disabling the ADC Channel
Use the following function can close the ADC channel :
An ADC channel can be disabled through the following function:
Hardware timers generally have two modes of operation, timer mode and counter mode. No matter which mode is operated, it works by counting the pulse signal counted by the internal counter module. Here are some important concepts of timers.
**Counter mode:** Counts the external pulse.
**Timer mode**: Counts the internal pulse. Timers are often used as timing clocks for timing detection, timing response, and timing control.
**Timer mode **: Counts the internal pulse. Timers are often used as timing clocks for timing detection, timing response, and timing control.
**Counter mode**: The counter can count up or down. The maximum count value of a 16-bit counter is 65535, and the maximum value of a 32-bit counter is 4 294 967 295.
**Counter **: Counter can count up or down. The maximum count value of the 16-bit counter is 65535, and the maximum value of the 32-bit counter is 4294967295.
**Counting frequency **：As for the number of counts within the counter time unit under the timer mode, since the system clock frequency is fixed, the timer time can be calculated according to the counter count value. `Timing time = count value / count frequency`. For example, if the counting frequency is 1 MHz, the counter counts once is 1 / 1000000 second. That is, every 1 microsecond counter is incremented by one (or subtract one), at this time, the maximum timing capability of the 16-bit counter is 65535 microseconds, which is 65.535 milliseconds.
**Counting frequency**：Since the input frequency is usually fixed, the time it takes for the counter to reach its desired count number can be calculated from just the given frequency - `time = count value / count frequency`. For example, if the counting frequency is 1 MHz, the counter counts once every 1 / 1000000 seconds. That is, every 1 microsecond, the counter is incremented by one (or subtracted by one), at this time, the maximum timing capability of the 16-bit counter is 65535 microseconds, or 65.535 milliseconds.
Set the timer timeout callback function by the following function, this callback function will be called when the timer expires:
Set the timer timeout callback function with the following function - this is the function that will be called when the timer reaches its set count value:
@@ -146,11 +144,11 @@ The command control words available for the hardware timer device are as follows
| HWTIMER_CTRL_INFO_GET | get timer feature information |
| HWTIMER_CTRL_MODE_SET | set timer mode |
Get the timer parameter arg,which is a pointer to the structure struct rt_hwtimer_info, to save the obtained information.
Get the timer parameter argument, which is a pointer to the structure struct rt_hwtimer_info, to save the obtained information.
>Setting frequency is valid only when the timer hardware and driver support sets the counting frequency. Generally, the default frequency of the driving setting can be used.
>Setting frequency is valid only when the timer hardware and included driver set the counting frequency. Generally, the default frequency of the driving setting can be used.
When setting the timer mode, the parameter arg can take the following values：
When setting the timer mode, the parameter argument can take the following values：
| -RT_ERROR | the device has been completely shut down and cannot be closed repeatedly |
| other error code | fail to close the device |
To close the device interface and open the device interface should be used in pairs. When open a device, close the device after use , so that the device can be completely shut down, otherwise the device will remain a opening status.
When a timer device has been used and is not necessary anymore, it should be closed, otherwise the device will remain in an open status.
The I2C (Inter Integrated Circuit) bus is a half-duplex, bidirectional two-wire synchronous serial bus developed by PHILIPS. The I2C bus has only two signal lines, one is the bidirectional data line SDA (serial data), and the other is the bidirectional clock line SCL (serial clock). The SPI bus has two lines for receiving data and transmitting data between the master and slave devices, while the I2C bus uses only one line for data transmission and reception.
The I2C (Inter Integrated Circuit) bus is a half-duplex, bidirectional two-wire synchronous serial bus developed by Philips. The I2C bus has only two signal lines, one is the bidirectional data line SDA (serial data), and the other is the bidirectional clock line SCL (serial clock). Compared to the SPI bus, which has two lines for receiving data and transmitting data between the master and slave devices, the I2C bus uses only one line for data transmission and reception.
Like SPI, I2C works in a master-slave manner. Unlike SPI-master-multi-slave architecture, it allows multiple master devices to exist at the same time. Each device connected to the bus has a unique address, and the master device initiates data transfer, and generates a clock signal. The slave device is addressed by the master device, and only one master device is allowed at a time. As shown below:
Like SPI, I2C works in a master-slave manner. Unlike SPI-master-multi-slave architecture, it allows multiple master devices to exist at the same time. Each device connected to the bus has a unique address, and the master device initiates data transfer, and generates a clock signal. The slave device is addressed by the master device, and only one master device is allowed to communicate at a time. As shown below:
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@@ -12,7 +12,7 @@ The main data transmission format of the I2C bus is shown in the following figur
When the bus is idle, both SDA and SCL are in a high state. When the host wants to communicate with a slave, it will send a start condition first, then send the slave address and read and write control bits, and then transfer the data (host send or receive data). The host will send a stop condition when the data transfer ends. Each byte transmitted is 8 bits, with the high bit first and the low bit last. The different terms in the data transmission process are as follows:
When the bus is idle, both SDA and SCL are in a high state. When the host wants to communicate with a slave, it will send a start condition first, then send the slave address and read and write control bits, and then transfer the data (the host can send or receive data). The host will send a stop condition when the data transfer ends. Each byte transmitted is 8 bits, with the high bit first and the low bit last. The different terms in the data transmission process are as follows:
***Starting Condition：** When SCL is high, the host pulls SDA low, indicating that data transfer is about to begin.
The pins on the chip are generally divided into four categories: power supply, clock, control, and I/O. The I/O port is further divided into General Purpose Input Output (GPIO) and function multiplex I/O (such as SPI/I2C/UART, etc.) in the usage mode.
The pins on the chip are generally divided into four categories: power supply, clock, control, and I/O. The I/O pins are further divided into General Purpose Input Output (GPIO) and function-multiplexed I/O (such as SPI/I2C/UART, etc.) pins, referring to their usage mode.
Most MCU pins have more than one function. The internal structure of different pins is different and the functions are different. The actual function of the pin can be switched through different configurations. The main features of the General Purpose Input Output (GPIO) port are as follows:
Most MCU pins have more than one function. Their internal structure is different and their supported functionality are different. The actual function of the pin can be switched through different configurations. The main features of the General Purpose Input Output (GPIO) port are as follows:
* Programmable Interrupt: The interrupt trigger mode is configurable. Generally, there are five interrupt trigger modes as shown in the following figure:
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@@ -31,7 +31,7 @@ The application accesses the GPIO through the PIN device management interface pr
### Obtain Pin Number
The pin numbers provided by RT-Thread need to be distinguished from the chip pin numbers. They are not the same concept. The pin numbers are defined by the PIN device driver and are related to the specific chip. There are two ways to obtain the pin number: use the macro definition or view the PIN driver file.
The pin numbers provided by RT-Thread need to be distinguished from the chip pin numbers, which not the same. The pin numbers are defined by the PIN device driver and are related to the specific chip used. There are two ways to obtain the pin number: use the macro definition or view the PIN driver file.
#### Use Macro Definition
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@@ -157,7 +157,7 @@ status = rt_pin_read(BEEP_PIN_NUM);
### Bind Pin Interrupt Callback Function
To use the interrupt function of the pin, you can use the following function to configure a pin to some interrupt trigger mode and bind an interrupt callback function to the corresponding pin. When the pin interrupt occurs, the callback function will be executed. :
To use the interrupt functionality of a pin, you can use the following function to configure the pin to some interrupt trigger mode and bind an interrupt callback function to the corresponding pin. When the pin interrupt occurs, the callback function will be executed.:
@@ -8,7 +8,7 @@ PWM (Pulse Width Modulation) is a method of digitally encoding the level of an a
Above is a simple schematic diagram of PWM. Assuming that the timer works in a up-counter mode. When the count value is less than the threshold, it outputs a level state, such as a high level. When the count value is greater than the threshold, it outputs the opposite, such as a low level. When the count value reaches the maximum value, the counter recounts from 0 and returns to the original level state. The ratio of the high-level duration (pulse width) to the cycle time is the duty cycle, ranging from 0 to 100%. The high level of the above picture is just half of the cycle time, so the duty cycle is 50%.
One of the common PWM control scenarios is to adjust the brightness of the light or screen. The brightness can be adjusted according to the duty cycle. The PWM adjusts the brightness not continuously, but constantly lights up and turns off the screen. When the light is turned on and off fast enough, the naked eye will always think that it is always bright. In the process of on and off, the longer the light is off, the lower the brightness of the screen to the naked eye. The longer the light is on, the less time is spent and the screen will be brighter.
One of the common PWM control scenarios is to adjust the brightness of a light or screen. The brightness can be adjusted through changing the duty cycle. The PWM does not adjust the light continuously, rather it constantly turns the screen on and off. When the light is turned on and off fast enough, the naked eye will always think that it is always bright. In the process of switching it on and off, the longer the light is off, the lower the brightness of the screen to the naked eye. Conversely, the longer the light is on, the brighter the screen will appear.
To set the period and duty cycle of a channel of a PWM device, use the command `pwm_set pwm1 1 500000 5000`. The first parameter is the command, the second parameter is the PWM device name, the third parameter is the PWM channel, and the fourth parameter is PWM period(ns), the fifth parameter is the pulse width (ns).
To set the period and duty cycle of a channel of a PWM device, use the command `pwm_set pwm1 1 500000 5000`. The first parameter is the command, the second parameter is the PWM device name, the third parameter is the PWM channel, and the fourth parameter is PWM period (ns), the fifth parameter is the pulse width (ns).
```c
msh/>pwm_setpwm115000005000
msh/>
```
To enable a channel of the PWM device, use the command`pwm_enable pwm1 1`. The first parameter is the command, the second parameter is the PWM device name, and the third parameter is the PWM channel.
To enable a channel of the PWM device, use the command`pwm_enable pwm1 1`. The first parameter is the command, the second parameter is the PWM device name, and the third parameter is the PWM channel.
The RTC (Real-Time Clock) provides accurate real-time clock time, which can be used to generate information such as year, month, day, hour, minute, and second. At present, most real-time clock chips use a higher precision crystal oscillator as a clock source. In order to work when the main power supply is powered down, some clock chips will be powered by a battery to keep the time information valid.
The RT-Thread RTC device provides the basic services for the operating system's time system. In the face of more and more IoT scenarios, RTC has become the standard configuration of the product, and even in the secure transmission process such as SSL, RTC has become an indispensable part.
The RT-Thread RTC device provides the basic services for the operating system's time system. RTCs find many uses in IoT scenarios, and even in secure transmission processes such as SSL, RTC has become an indispensable part.
## Access RTC Devices
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@@ -119,7 +119,7 @@ RT-Thread online packages →
[*]EnableNTP(NetworkTimeProtocol)client
```
After the NTP is turned on, the RTC's automatic synchronization function will be automatically turned on, and the synchronization period and the delay time of the first synchronization can also be set:
After NTP is turned on, the RTC's automatic synchronization function will be automatically turned on, and the synchronization period and the delay time of the first synchronization can also be set:
Sensor is an important part of the Internet of Things, and "Sensor to the Internet of Things" is equivalent to "eyes to humans". Without eyes, human beings can not see the vast world of flowers. The same is true for the Internet of Things.
Sensors are an important part of the Internet of Things, and sensors in an IoT system are equivalent to the eyes of humans. Without eyes, human beings can not see and interpret the world around them. The same is true for the Internet of Things.
Nowadays, with the development of Internet of Things, a large number of Sensors have been developed for developers to choose, such as Accelerometer, Magnetometer, Gyroscope, Barometer/pressure, Humidometer and so on. These sensors, manufactured by the world's leading semiconductor manufacturers, have increased market selectivity and made application development more difficult. Because different sensor manufacturers and sensors need their own unique drivers to run, so when developing applications, they need to adapt to different sensors, which naturally increases the difficulty of development. In order to reduce the difficulty of application development and increase the reusability of sensor driver, we designed a Sensor device.
Nowadays, with the development of IoT, a large number of sensors are available for developers to choose, such as Accelerometers, Magnetometers, Gyroscopes, Barometers/pressure senosrs, Hygrometers/humidity meters and so on. However, these sensors, manufactured by the world's leading semiconductor manufacturers, have increased market selectivity and made application development more difficult. Because different sensor manufacturers and sensors need their own unique drivers to run, developers need to write a device driver for each sensor, which can be difficult and time-consuming. In order to reduce the difficulty of application development and increase the reusability of sensor driver, we designed a Sensor device.
The function of Sensor device is to provide a unified operation interface for the upper layer and improve the reusability of the upper code.
The function of the Sensor device is to provide a unified operation interface for the upper layer and improve the reusability of the upper code.
### Characteristics of Sensor Device
### Characteristics of the Sensor Device
-**Interface**: Standard device interface (open/close/read/control)
-**Work mode**: support polling, interruption, FIFO three modes
-**Power mode**: support four modes: power failure, common, low power consumption and high power consumption
-**Interface:** Standard device interface (open/close/read/control)
-**Work mode:** Supports polling, interrupts, three FIFO (First In, First Out) modes
-**Power mode:** support four modes: power failure, common, low power consumption and high power consumption
Through the device handle, the application can open and close the device. When the device is opened, it will check whether the device has been initialized or not. If it is not initialized, it will call the initialization interface initialization device by default. Open the device through the following functions:
Through the device handle, the application can open and close the device. When the device is opened, it will check whether the device has been initialized or not. If it is not initialized, it will call the initialization interface by default. Open the device through the following functions:
@@ -79,7 +79,7 @@ The oflags parameter supports the following parameters：
There are three modes of receiving and sending sensor data: interrupt mode, polling mode and FIFO mode. When using these three modes, **only one of them can be chosen**. If the sensor's open parameter oflags does not specify the use of interrupt mode or FIFO mode, polling mode is used by default.
FIFO ,means first Input first output. FIFO transmission mode needs sensor hardware support, data is stored in hardware FIFO, read multiple data at a time, which saves CPU resources to do other operations. Very useful in low power mode
FIFO transmission mode needs sensor hardware support, data is stored in hardware FIFO, which reads and stores multiple data simultaneously, which allows the CPU to do other operations while gathering data. This feature is very useful in low power mode.
If the sensor uses FIFO receiving mode, the value of oflags is RT_DEVICE_FLAG_FIFO_RX.
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@@ -109,7 +109,7 @@ int main(void)
### Control Sensor Device
By command control word, the application program can configure the sensor device through the following functions:
By command control words, the application program can configure the sensor device through the following functions:
The callback function of the function is provided by the user. If the sensor is opened in interrupt mode, when the sensor receives data and interrupts, the callback function will be called, and the data size of the buffer will be placed in the `size` parameter, and the sensor device handle will be placed in the `dev` parameter for users to obtain.
The callback function of the function is provided by the user. If the sensor is opened in interrupt mode, as the sensor receives data the callback function will be called. The data size of the buffer will be placed in the `size` parameter, and the sensor device handle will be placed in the `dev` parameter for users to obtain.
Generally, receiving callback function can send a semaphore or event to inform sensor data processing thread that data arrives. The use example is as follows:
