我在 Raspberry Pi 3 B+ 上使用 Python 3 操作 AD5272 时遇到问题。AD5272是带I2C接口的数控变阻器（我的部分电阻为20 kOhm）。
问题如下：
A 和 W 端子之间的电阻不会改变我尝试设置的任何位置，并且保持在 10KOhm 左右。（默认情况下，当 AD5272 开启时，将在那里设置全电阻的一半）。当我从 RDAC 读取电阻时 - 读取零电阻。
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()
输出是：
Binary representation of position for RDAC : 0b1111111111
MSB : 0b1011
LSB : 0b11111111
All Bytes : 0b101111111111
Value : 20000.0
4096
0
电脑：树莓派 3，型号 B+
操作系统：Raspbian 9
Python版本：3.5.3
I2C 封装：smbus2
零件编号：AD5272BRMZ-20
数据表：http: //www.farnell.com/datasheets/1706490.pdf
我做错了什么以及如何解决？
零件的接线经过三重检查。无论我试图在那里写入什么值，从 RDAC 读取的内容总是相同的。我尝试了两个命令：
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)
结果总是一样的：阻力没有改变。用外部欧姆计装置检查电阻。
请帮忙！