The Raspberry Pi Sensor Expansion Board is designed specifically for the convenience of external sensors for Raspberry Pi. This expansion board is suitable for Raspberry Pi Zero/Zero W/Zero WH/A+/B+/2B/3B/3B+/4B. The Raspberry Pi can be powered through a 5.5-2.1mm DC head or terminal block. RF24L01 module, HC-SR04 ultrasonic module, I2C interface, UART interface are reserved, supporting 8 ADC channels. At the same time, free up the camera and display cable interface.
The Raspberry Pi expansion board is labeled with BCM codes and function names for signal pins, as shown in the following figure:
- Built-in 10bit ADC MCU， Support 8-channel ADC detection rang0~1023;
- Support Raspberry Pi 2B/3B/3B+/4B/zero；
- 5.5x2.1 DC head and terminal power supply，input rang 7 ~30V;
- Freely switch between external sensor voltage 3V3 and 5V;
- Onboard DC-DC step-down chip Voltage output: 5V 3A
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Working voltage: 3.3V and 5V. Select the ADC detection voltage based on the jumper cap;
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Communication method with Raspberry Pi: I2C，speed 1~400K;
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IO: 8-channel ADC detection，pin name A0~A7;
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I2C address: 0x24，can redefine i2c address;
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8-channel expansion mode supports ADC input, GPIO, PWM (only A1-A2 supported)
The MCU I2C address of the expansion board is 0x24, and the registered address is explained as follows:
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0x10 ~ 0x17: read ADC raw data
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0x20 ~ 0x27: read input voltage(mv)
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0x30 ~ 0x37: read the ratio of input voltage to output voltage Input voltage / output voltage(0~100)
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0x40 ~ 0x47: read or write pin A0-A7 digital value
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0x51 ~ 0x52: set A1-A2 PWM duty
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0x61 ~ 0x62: set A1-A2 PWM frequency
Open the Raspberry Pi terminal and enter the "sudo raspi-config" command, then follow the sequence shown below.
The above is to open the Raspberry Pi I2C. Next, we install the Raspberry I2C library and type "sudo apt-get install i2c-tools" in the terminal. After the input is complete, you can see that the I2C library is being downloaded. After the installation is complete, you can enter " sudo i2cdetect -l "detects whether the installation is correct. If a message similar to the following appears, the installation is normal.
Enter "sudo i2cdetect -y 1" command in the terminal to scan all I2C devices connected to the I2C bus and print out the I2C bus address of the device, and the I2C address of our expansion board is 0x24.
!!! Edit the config.txt file to set the Raspberry Pi IIC bus speed
sudo nano /boot/config.txt
Look for the line that contains "dtParam =i2c_arm=on" and add ", i2c_arm_baudrate=100000 "where 100000 is the new speed (100kbit /s), notice the comma before i2c. The complete code is as follows:
dtparam=i2c_arm=on,i2c_arm_baudrate=100000
This enables the I2C bus and also completes the new baud rate setup. When you're finished editing, use Ctrl-X, then Y, save the file and exit. Restart Raspberry Pi to make the new Settings take effect:
sudo reboot
As we all know, there is no ADC in Raspberry Pi, so the analog value of the sensor cannot be read directly. With the help of the ADC MCU built into the expansion board, a 10-bit ADC can be read. This means that analog sensors can be used on the Raspberry Pi, and there are a total of 8 available interfaces A0~A7.
run python demo before，please install smbus2 as cmd:
pi@raspberrypi: pip3 install smbus2 #coding=utf-8
from sensor_expansion_board_i2c import IoExpansionBoardI2c
from smbus2 import SMBus
import time
i2c_bus = 1
i2c_address = 0x24
io_expansion_board_i2c = IoExpansionBoardI2c(i2c_bus, i2c_address)
for i in range(8):
io_expansion_board_i2c[i].mode = IoExpansionBoardI2c.ADC_MODE
try:
while True:
print('A0:',io_expansion_board_i2c[0].adc_value)
print('A1:',io_expansion_board_i2c[1].adc_value)
print('A2:',io_expansion_board_i2c[2].adc_value)
print('A3:',io_expansion_board_i2c[3].adc_value)
print('A4:',io_expansion_board_i2c[4].adc_value)
print('A5:',io_expansion_board_i2c[5].adc_value)
print('A6:',io_expansion_board_i2c[6].adc_value)
print('A7:',io_expansion_board_i2c[7].adc_value)
time.sleep(1)
except KeyboardInterrupt:
pass用python3运行demo
pi@raspberrypi:~/$ python3 adc.py
This routine is written in C++language for Raspberry Pi, with pin A0 outputting high and low levels at intervals of 100ms
#include <iostream>
#include <chrono>
#include <thread>
#include "gpio_expansion_board.h"
GpioExpansionBoard gpio_expansion_board;
int main() {
std::cout << "Setup" << std::endl;
if (!gpio_expansion_board.SetGpioMode(GpioExpansionBoard::kGpioPinE0,
GpioExpansionBoard::kOutput)) {
std::cerr << "Failed to set GPIO mode" << std::endl;
return -1;
}
while (true) {
std::cout << "Setting GPIO A0 to HIGH" << std::endl;
if (!gpio_expansion_board.SetGpioLevel(GpioExpansionBoard::kGpioPinE0, 1)) {
std::cerr << "Failed to set GPIO level HIGH" << std::endl;
return -1;
}
std::this_thread::sleep_for(std::chrono::milliseconds(100));
std::cout << "Setting GPIO A0 to LOW" << std::endl;
if (!gpio_expansion_board.SetGpioLevel(GpioExpansionBoard::kGpioPinE0, 0)) {
std::cerr << "Failed to set GPIO level LOW" << std::endl;
return -1;
}
std::this_thread::sleep_for(std::chrono::milliseconds(100));
}
gpio_expansion_board.SetGpioLevel(GpioExpansionBoard::kGpioPinE0, 0);
std::cout << "Program terminated" << std::endl;
return 0;
}use g++ cmd build as follows
pi@raspberrypi:~/sensor_expansion_board_python_demo/src $
g++ -lwiringPi -I./ digital_output/digital_output.cpp gpio_expansion_board.cpp -o gpio_out
pi@raspberrypi:~/sensor_expansion_board_python_demo/src $./gpio_out
Setup
Setting GPIO A0 to HIGH
Setting GPIO A0 to LOW
Setting GPIO A0 to HIGH
Setting GPIO A0 to LOW