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1.15. SPI之max31865

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1.15.1. Max31865

MAX31865是一款集成的的单芯片RTD数字转换器,用于替代多个分立元件来降低成本。它提供简单而准确的温度测量,非常适合用于测量和过程控制,是在工业领域最常用的测量方案。

MAX31865完全集成了RTD数字转换器,单芯片方案降低了系统成本(CD约50%)和系统的复杂度,尤其适用于工业中最常用的铂RTD (如Pt100或Pt1000),解决了电阻->数字转换问题。

典型特征:

u 简单地解决了铂RTD电阻数字化问题

u 适用PT100、PT1000

u 适用于2线、3线、4线接法

u wps49转换时间≤21ms

u 15bits ADC精度

u 全局精度≤0.5℃

u 输入保护±50V

u 查分输入

u 检测机制

u SPI总线

u 20-PIN TQFN封装

TQFN封装手工焊有难度,故实验中采用某宝采购的模块和3线PT100,如上图所示。

1.15.2. SPI总线

ESP32的micropython固件,内置硬件spi模块SPI(spi1、spi2)和软件spi模块SoftSPI。SPI模块/SoftSPI模块作为machine的子模块,与Pin/I2C/Uart等处于同级目录。

下图摘自micropython官网:

wps50

wps51

实际使用时,硬件spi/软件spi均可满足使用要求,本实验中使用软件spi。

1.15.3. 接线

Pin

MAX31865

ESP32-WROOM-32

CS

CS

D4

SDI

Sdi

D23

SDO

sdo

D19

SCK

sck

D18

wps52

1.15.4. 读取温度

代码实现如下:

 1 from time import sleep,sleep_ms
 2 from machine import SPI,Pin,SoftSPI
 3 
 4 cs = Pin(4,Pin.OUT)
 5 max31865 = SoftSPI(baudrate=1000000,\
 6                    polarity=0,phase=1,\
 7                    firstbit=SPI.MSB,\
 8                    sck=Pin(18),\
 9                    mosi=Pin(23),\
10                    miso=Pin(19))
11 
12 max31865.init()
13 
14 DEBUG = False
15 
16 def config(value=b'\x80\xd3'):
17     cs.off()
18     max31865.write(value)
19     cs.on()
20     pass
21 
22 def readConfig():
23     cs.off()
24     max31865.write(b'\x00')
25     config = max31865.read(1)
26     cs.on()
27     if DEBUG:
28         print(config) 
29 
30 def readADC():
31     cs.off()
32     max31865.write(b'\x01')
33     msb = max31865.read(1)
34     lsb = max31865.read(1)
35     cs.on()
36     if DEBUG:
37         print("\t->msb:"+str(msb)+";lsb:"+str(lsb))
38     return(msb[0],lsb[0])
39 
40 def readHFault():
41     cs.off()
42     max31865.write(b'\x03')
43     msb = max31865.read(1)
44     lsb = max31865.read(1)
45     cs.on()
46     if DEBUG:
47         print("\t->hfmsb:"+str(msb)+";hflsb:"+str(lsb))
48 
49 def readLFault():
50     cs.off()
51     max31865.write(b'\x05')
52     msb = max31865.read(1)
53     lsb = max31865.read(1)
54     cs.on()
55     if DEBUG:
56         print("\t->lfmsb:"+str(msb)+";lflsb:"+str(lsb))
57 
58 def readFault():
59     cs.off()
60     max31865.write(b'\x07')
61     config = max31865.read(1)
62     cs.on()
63     if DEBUG:
64         print("\tfault:",config)
65 
66 Config()
67 
68 while True:
69     '''
70         max31865手册p19,r_pt=100Ω对应0℃,
71 r_pt=111.67Ω对应30℃,带入公式
72         t = r*a+b可得a = 2.57,b=-257
73         ∴temperature = 2.57*r_pt - 257
74     '''
75 
76     m,l = readADC()
77     adc_code = (((m*256)+l)>>1)
78     temp = ((adc_code/32) -256)
79     r_pt = ((adc_code*430)/32768)
80     print("R:",r_pt)
81     print("temperature:%3.2f ℃" %(2.57*r_pt-257))
82     sleep(1)

 

注意:max31865 datasheet说明

a. 连续转换时不要改变config寄存器D0值;

b. Max31865支持spi模式1/3,所以phase必须为1;

c. 高字节在前,MSB模式;

wps53wps54

1.15.5. 抽象为模块

Max31865驱动模块源码:

  1 from time import sleep,sleep_ms
  2 from machine import SPI,Pin,SoftSPI
  3 
  4 class MAX31865:
  5     def __init__(self,\
  6                  sck,\
  7                  mosi,\
  8                  miso,\
  9                  cs,\
 10                  baudrate=1000000,\
 11                  polarity=0,\
 12                  phase=1,\
 13                  firstbit=SPI.MSB,\
 14                  debug=False,\
 15                  compensation=0):
 16         '''
 17                 默认
 18                 baudrate=1000000 10M
 19                 polarity=0
 20                 phase =1
 21                 MSB
 22                 compensation=0
 23         '''
 24 
 25         self.cs = Pin(cs,Pin.OUT)
 26         self.max31865 = SoftSPI(baudrate=baudrate,\
 27                                polarity=polarity,phase=phase,\
 28                                firstbit=SPI.MSB,\
 29                                sck=Pin(sck),\
 30                                mosi=Pin(mosi),\
 31                                miso=Pin(miso))
 32         self.compensation = compensation
 33         self.max31865.init()
 34         self.DEBUG = debug
 35         self.config()
 36 
 37     def config(self,value=b'\x80\xd3'):
 38         '''
 39             默认:
 40             连续转换 bias on
 41         '''
 42         self.cs.off()
 43         self.max31865.write(value)
 44         self.cs.on()
 45         pass
 46 
 47     def readConfig(self):
 48         '''
 49         读配置寄存器
 50         '''
 51         self.cs.off()
 52         self.max31865.write(b'\x00')
 53         config = self.max31865.read(1)
 54         self.cs.on()
 55         if self.DEBUG:
 56             print(config)
 57         return(config)
 58 
 59     def readADC(self):
 60         '''
 61         读ADC值
 62         '''
 63         self.cs.off()
 64         self.max31865.write(b'\x01')
 65         msb = self.max31865.read(1)
 66         lsb = self.max31865.read(1)
 67         self.cs.on()
 68         if self.DEBUG:
 69             print("\t->msb:"+str(msb)+";lsb:"+str(lsb))
 70         return(msb[0],lsb[0])
 71 
 72     def readHFault(self):
 73         '''
 74         读上界限寄存器
 75         '''       
 76         self.cs.off()
 77         self.max31865.write(b'\x03')
 78         msb = self.max31865.read(1)
 79         lsb = self.max31865.read(1)
 80         self.cs.on()
 81         if self.DEBUG:
 82             print("\t->hfmsb:"+str(msb)+";hflsb:"+str(lsb))
 83         return(msb[0],lsb[0])
 84 
 85     def readLFault(self):
 86         '''
 87         读下界限寄存器
 88         '''       
 89         self.cs.off()
 90         self.max31865.write(b'\x05')
 91         msb = self.max31865.read(1)
 92         lsb = self.max31865.read(1)
 93         self.cs.on()
 94         if self.DEBUG:
 95             print("\t->hfmsb:"+str(msb)+";hflsb:"+str(lsb))
 96         return(msb[0],lsb[0])
 97 
 98     def readFault(self):
 99         '''
100         读错误
101         '''       
102         self.cs.off()
103         self.max31865.write(b'\x07')
104         config = self.max31865.read(1)
105         self.cs.on()
106         if self.DEBUG:
107             print("\tfault:",config)
108         return(config)
109 
110     def readTemperature(self):
111         '''
112         读温度值
113         '''
114         m,l = self.readADC()
115         adc_code = (((m*256)+l)>>1)
116         temp = ((adc_code/32) -256)
117         r_pt = ((adc_code*430)/32768)
118         temperature = (2.57*r_pt-257+self.compensation)
119         return(temperature)                                        

Main.py文件示例:

1 from max31865 import MAX31865
2 from time import sleep
3 
4 sensor = MAX31865(18,23,19,4)
5 
6 while True:
7     print("Temperature:%3.2f" %(sensor.readTemperature()))
8     sleep(1)

 

运行效果如下图:

wps55

标签:1.15,lsb,read,self,SPI,max31865,cs,msb
来源: https://www.cnblogs.com/horal/p/16514117.html