在Raspberry Pi 3 B +上使用Python 3和smbus2操作AD5272 B +
我在Raspberry Pi 3 B +上使用Python 3操作AD5272时出现问题。 AD5272是带有I2C接口的数字控制变阻器(我的部件具有20 kOhm的电阻)。在Raspberry Pi 3 B +上使用Python 3和smbus2操作AD5272 B +
问题是以下几点:
A和W端之间的电阻不改变任何位置我试图建立和周围为10Mohm停留。 (默认情况下,当AD5272打开时,设置全部电阻的一半)。 当我读取RDAC的阻力时 - 读取零阻力。
这是我的代码:
#!/usr/bin/python3
import smbus2
import time, os
class AD527x():
# command bits which are dependant on I2C address of device
def __init__ (self, bus=1, address=0x2E, resistance = 20000, positions = 1023, reset = False):
self.bus = smbus2.SMBus(bus)
self.positions = positions
self.address = address
self.resistance = resistance
def write_position (self, position):
# sets the rheostat to certain position
# if wiper position is higher than maximal
if position > self.positions:
position = self.positions
# approximate resistance of rheostat
resistance = self.resistance*position/self.positions
# for AD5274 needs to be shifted for 2 digits left
if self.positions == 256:
position = position << 2
print ("Binary representation of position for RDAC : " + bin (position))
# Writing position is sneding 2 bytes one by one
# MSB Data: 0 0 C3 C2 C1 C0 D9 D8
# For writing command bytes: C3 = 0; C2 = 0; C1 = 0; C0 = 1
# 0 0 0 0 0 1 ? ?
# ? ? - MSB of 10-digit binary representation of wiper position between 0 and 1023
# two first positions : D9_8 = (position & 0b1100000000) >> 8
MSB = (1 << 3) | ((position & 0b1100000000) >> 8)
print ("MSB : " + bin(MSB))
# take last 8 bits
LSB = position & 0b11111111
print ("LSB : " + bin(LSB))
print ("All Bytes : " + bin((MSB << 8) +LSB))
print ("Value : " + str(resistance))
self.bus.write_i2c_block_data(self.address, 0, [MSB, LSB])
self.read_position()
def read_position (self):
# reads current position of rheostat
# prepare the circuit to send data
# MSB Data: 0 0 C3 C2 C1 C0 D9 D8
# For reading command bytes: C3 = 0; C2 = 0; C1 = 1; C0 = 0
# 0 0 0 0 1 0 ? ?
# ? ? - Doen't matter - Just use zeros
# LSB - doesn't matter, just using 0b00000000
MSB = 0b00001000
LSB = 0b00000000
self.bus.write_i2c_block_data(self.address, 0, [MSB, LSB])
#read 2 bytes from RDAC
a = self.bus.read_byte(self.address)
time.sleep (0.005)
b = self.bus.read_byte(self.address)
value = ((a << 8) | b)
print (value)
# take 10 lats bits only
value = value & 0b1111111111
print (value)
def main():
device = AD527x()
device.write_position(1023)
if __name__ == "__main__":
main()
的输出是:
Binary representation of position for RDAC : 0b1111111111
MSB : 0b1011
LSB : 0b11111111
All Bytes : 0b101111111111
Value : 20000.0
4096
0
计算机:Rapberry裨3,模型B +
OS:Raspbian 9
Python的版本: 3.5.3
I2C包:smbus2
型号:AD5272BRMZ-20
数据表:http://www.farnell.com/datasheets/1706490.pdf
什么我做错了,如何解决呢?
零件的接线是三重检查的。从RDAC读取的数据总是相同的,无论我试图在那里写什么值。我想这两个命令:
self.bus.write_i2c_block_data(self.address, 0, [MSB, LSB])
和
self.bus.write_byte (self.address, MSB)
self.bus.write_byte (self.address, LSB)
结果总是相同的:阻力不会改变。用外部欧姆表装置检查电阻。
请帮忙!
我刚刚遇到同样的问题。我还没有看过与Python的接口,但这可能有帮助。
在我的电路中,AD5272 I2C使用GND寻址,端子A连接到VDD(5V),W串联一个100K电阻连接到GND。
首先我确保设备通过Linux驱动程序运行,模块应该已经内置。作为根:
$ echo ad5272 0x2f > /sys/bus/i2c/devices/i2c-1/new_device
$ dmesg | tail -n 2
[ 711.195428] i2c i2c-1: new_device: Instantiated device ad5272 at 0x2f
[ 711.242537] ad_dpot 1-002f: ad5272 1024-Position Digital Potentiometer registered
$ cat /sys/bus/i2c/devices/1-002f/rdac0
511
$ echo 0 > /sys/bus/i2c/devices/1-002f/rdac0
$ cat /sys/bus/i2c/devices/1-002f/rdac0
0
$ echo 1023 > /sys/bus/i2c/devices/1-002f/rdac0
$ cat /sys/bus/i2c/devices/1-002f/rdac0
1023
测量从W到GND的电压,得到〜5V在0和〜2.5V在1023
我然后与连接到I2C总线逻辑分析器重复。用于写的命令是:
0x5e 0x1c 0x03 0x5e 0x04 0x00
0x5e 0x1c 0x03 0x5e 0x07 0xff
这样应该可以提供一个提示,重新读取数据表中的部分上“写保护”和“控制寄存器的说明”。在我的设置我只希望使用数字接口,而不是存储控制存储器,所以我从用户空间复制有轻微的改变:
sudo i2cset 1 0x2f 0x1c 0x02 b
sudo i2cset 1 0x2f 0x04 0x00 b
sudo i2cset 1 0x2f 0x07 0xff b
我会尽力做到这一点。现在我认为这个问题可能是在I2C接口的Python实现中。我注意到一些组件重新调用特定的I2C时钟速度。 – Iegor