樹(shù)莓派從零開(kāi)始快速入門(mén)第11講——SPI（以O(shè)LED為例）

一、前言

SPI是外設(shè)驅(qū)動(dòng)常用的通訊方式之一，相比于IIC，SPI數(shù)據(jù)傳輸的速率要更高，因?yàn)镾PI比IIC多了一根數(shù)據(jù)線，是全雙工的。具體的通訊原理這里就不多介紹了，我主要講解樹(shù)莓派的SPI編程部分。因?yàn)槲业臄U(kuò)展板只有OLED連的是SPI接口，所以這一講就以O(shè)LED為例。

二、使能樹(shù)莓派SPI接口

方法1：通過(guò)配置命令

sudo raspi-config    // 打開(kāi)配置
sudo reboot          // 重啟，如果之前沒(méi)有使能，配置完之后要重啟才能生效

方法2：在可視化界面的設(shè)置里面修改

如果之前沒(méi)有使能，配置完之后要重啟才能生效

三、編寫(xiě)程序及運(yùn)行

SPI通訊主要用的是spidev庫(kù)，該庫(kù)的api可以參考下面這個(gè)鏈接。

spidev庫(kù)：https://pypi.org/project/spidev

圖像文字顯示主要用的是python圖像處理PIL庫(kù)，關(guān)于這個(gè)庫(kù)的詳細(xì)情況可以參考下面這篇博文，https://blog.csdn.net/zhangziju/article/details/79123275

代碼主要分成兩部分：驅(qū)動(dòng)部分和應(yīng)用部分

驅(qū)動(dòng)部分是通過(guò)spi和SSD1306芯片通信，實(shí)現(xiàn)顯示數(shù)據(jù)的傳輸。

應(yīng)用部分就是根據(jù)你的需求，在對(duì)應(yīng)的位置顯示你想要的內(nèi)容。

驅(qū)動(dòng)部分代碼如下：

SSD1306.py

import spidev
import RPi.GPIO as GPIO
import time

# Constants
SSD1306_SETCONTRAST = 0x81
SSD1306_DISPLAYALLON_RESUME = 0xA4
SSD1306_DISPLAYALLON = 0xA5
SSD1306_NORMALDISPLAY = 0xA6
SSD1306_INVERTDISPLAY = 0xA7
SSD1306_DISPLAYOFF = 0xAE
SSD1306_DISPLAYON = 0xAF
SSD1306_SETDISPLAYOFFSET = 0xD3
SSD1306_SETCOMPINS = 0xDA
SSD1306_SETVCOMDETECT = 0xDB
SSD1306_SETDISPLAYCLOCKDIV = 0xD5
SSD1306_SETPRECHARGE = 0xD9
SSD1306_SETMULTIPLEX = 0xA8
SSD1306_SETLOWCOLUMN = 0x00
SSD1306_SETHIGHCOLUMN = 0x10
SSD1306_SETSTARTLINE = 0x40
SSD1306_MEMORYMODE = 0x20
SSD1306_COLUMNADDR = 0x21
SSD1306_PAGEADDR = 0x22
SSD1306_COMSCANINC = 0xC0
SSD1306_COMSCANDEC = 0xC8
SSD1306_SEGREMAP = 0xA0
SSD1306_CHARGEPUMP = 0x8D
SSD1306_EXTERNALVCC = 0x1
SSD1306_SWITCHCAPVCC = 0x2

# Scrolling constants
SSD1306_ACTIVATE_SCROLL = 0x2F
SSD1306_DEACTIVATE_SCROLL = 0x2E
SSD1306_SET_VERTICAL_SCROLL_AREA = 0xA3
SSD1306_RIGHT_HORIZONTAL_SCROLL = 0x26
SSD1306_LEFT_HORIZONTAL_SCROLL = 0x27
SSD1306_VERTICAL_AND_RIGHT_HORIZONTAL_SCROLL = 0x29
SSD1306_VERTICAL_AND_LEFT_HORIZONTAL_SCROLL = 0x2A


class SSD1306(object):
    """class for SSD1306  128*64 0.96inch OLED displays."""

    def __init__(self, rst, dc, spi):
        self.width = 128
        self.height = 64
        self._pages = 8
        self._buffer = [0]*(self.width*self._pages)
        # Initialize DC RST pin
        self._dc = dc
        self._rst = rst
        GPIO.setmode(GPIO.BCM)
        GPIO.setwarnings(False)
        GPIO.setup(self._dc, GPIO.OUT)
        GPIO.setup(self._rst, GPIO.OUT)
        # Initialize SPI
        self._spi = spi

    def command(self, cmd):
        """Send command byte to display"""
        GPIO.output(self._dc, GPIO.LOW)
        self._spi.writebytes([cmd])

    def data(self, val):
        """Send byte of data to display"""
        GPIO.output(self._dc, GPIO.HIGHT)
        self._spi.writebytes([val])

    def begin(self, vccstate=SSD1306_SWITCHCAPVCC):
        """Initialize dispaly"""
        self._vccstate = vccstate
        self.reset()
        self.command(SSD1306_DISPLAYOFF)                    # 0xAE
        self.command(SSD1306_SETDISPLAYCLOCKDIV)            # 0xD5
        self.command(0x80)                     # the suggested ra    tio 0x80

        self.command(SSD1306_SETMULTIPLEX)                  # 0xA8
        self.command(0x3F)
        self.command(SSD1306_SETDISPLAYOFFSET)              # 0xD3
        self.command(0x0)                                   # no offset
        self.command(SSD1306_SETSTARTLINE | 0x0)            # line #0
        self.command(SSD1306_CHARGEPUMP)                    # 0x8D
        if self._vccstate == SSD1306_EXTERNALVCC:
            self.command(0x10)
        else:
            self.command(0x14)
        self.command(SSD1306_MEMORYMODE)                    # 0x20
        self.command(0x00)                            # 0x0 act like ks0108
        self.command(SSD1306_SEGREMAP | 0x1)
        self.command(SSD1306_COMSCANDEC)
        self.command(SSD1306_SETCOMPINS)                    # 0xDA
        self.command(0x12)
        self.command(SSD1306_SETCONTRAST)                   # 0x81
        if self._vccstate == SSD1306_EXTERNALVCC:
            self.command(0x9F)
        else:
            self.command(0xCF)
        self.command(SSD1306_SETPRECHARGE)                  # 0xd9
        if self._vccstate == SSD1306_EXTERNALVCC:
            self.command(0x22)
        else:
            self.command(0xF1)
        self.command(SSD1306_SETVCOMDETECT)                 # 0xDB
        self.command(0x40)
        self.command(SSD1306_DISPLAYALLON_RESUME)           # 0xA4
        self.command(SSD1306_NORMALDISPLAY)                 # 0xA6
        self.command(SSD1306_DISPLAYON)

    def reset(self):
        """Reset the display"""
        GPIO.output(self._rst, GPIO.HIGH)
        time.sleep(0.001)
        GPIO.output(self._rst, GPIO.LOW)
        time.sleep(0.010)
        GPIO.output(self._rst, GPIO.HIGH)

    def display(self):
        """Write display buffer to physical display"""
        self.command(SSD1306_COLUMNADDR)
        self.command(0)  # Cloumn start address
        self.command(self.width-1)  # Cloumn end address
        self.command(SSD1306_PAGEADDR)
        self.command(0)  # Page start address
        self.command(self._pages-1)  # Page end address
        # Write buffer data
        GPIO.output(self._dc, GPIO.HIGH)
        self._spi.writebytes(self._buffer)

    def image(self, image):
        """Set buffer to value of Python Imaging Library image."""
        if image.mode != '1':
            raise ValueError('Image must be in mode 1.')
        imwidth, imheight = image.size
        if imwidth != self.width or imheight != self.height:
            raise ValueError('Image must be same dimensions as display 
				({0}x{1}).' .format(self.width, self.height))

        pix = image.load()
        # Iterate through the memory pages
        index = 0
        for page in range(self._pages):
            # Iterate through all x axis columns.
            for x in range(self.width):
                # Set the bits for the column of pixels at the current position.
                bits = 0
                # Don't use range here as it's a bit slow
                for bit in [0, 1, 2, 3, 4, 5, 6, 7]:
                    bits = bits << 1
                    bits |= 0 if pix[(x, page*8+7-bit)] == 0 else 1
                # Update buffer byte and increment to next byte.
                self._buffer[index] = bits
                index += 1

    def clear(self):
        """Clear contents of image buffer"""
        self._buffer = [0]*(self.width*self._pages)

    def set_contrast(self, contrast):
        """Sets the contrast of the display.
        Contrast should be a value between 0 and 255."""
        if contrast < 0 or contrast > 255:
            raise ValueError('Contrast must be a value from 0 to 255).')
        self.command(SSD1306_SETCONTRAST)
        self.command(contrast)

    def dim(self, dim):
        """Adjusts contrast to dim the display if dim is True, 
        otherwise sets the contrast to normal brightness if dim is False."""
        # Assume dim display.
        contrast = 0
        # Adjust contrast based on VCC if not dimming.
        if not dim:
            if self._vccstate == SSD1306_EXTERNALVCC:
                contrast = 0x9F
            else:
                contrast = 0xCF

應(yīng)用部分代碼如下：

oled.py

import spidev as SPI
import SSD1306
import time

from PIL import Image,ImageDraw,ImageFont
 
# Raspberry Pi pin configuration:
RST = 19
DC = 16
bus = 0 
device = 0 

# 128x64 display with hardware SPI:
disp = SSD1306.SSD1306(RST, DC, SPI.SpiDev(bus, device))

# Initialize library.
disp.begin()
 
# Clear display.
disp.clear()
disp.display()

# Create blank image for drawing.
# Make sure to create image with mode '1' for 1-bit color.
width = disp.width
height = disp.height
image = Image.new('1', (width, height))
 
# Get drawing object to draw on image.
draw = ImageDraw.Draw(image)
 
# Draw a black filled box to clear the image.
draw.rectangle((0,0,width,height), outline=0, fill=0)
 
# Draw some shapes.
# First define some constants to allow easy resizing of shapes.
padding = 2
shape_width = 20
top = padding
bottom = height-padding
# Move left to right keeping track of the current x position for drawing shapes.
x = padding
# Draw an ellipse.
draw.ellipse((x, top , x+shape_width, bottom), outline=255, fill=0)
x += shape_width+padding
# Draw a rectangle.
draw.rectangle((x, top, x+shape_width, bottom), outline=255, fill=0)
x += shape_width+padding
# Draw a triangle.
draw.polygon([(x, bottom), (x+shape_width/2, top), (x+shape_width, bottom)], outline=255, fill=0)
x += shape_width+padding
# Draw an X.
draw.line((x, bottom, x+shape_width, top), fill=255)
draw.line((x, top, x+shape_width, bottom), fill=255)
x += shape_width+padding
 
# Load default font.
font = ImageFont.load_default()
 
# Write two lines of text.
draw.text((x, top),    'Hello',  font=font, fill=255)
draw.text((x, top+20), 'World!', font=font, fill=255)
 
# Display image.
disp.image(image)
disp.display()

運(yùn)行結(jié)果：
運(yùn)行oled.py，OLED從左到右分別顯示的是一個(gè)橢圓形，一個(gè)矩形，一個(gè)三角形，一個(gè)字母“X”，兩個(gè)字符串Hello world！（攝像頭怎么拍都拍不好將就著看吧）

四、進(jìn)階學(xué)習(xí)

1、顯示中文

PIL默認(rèn)的字庫(kù)是沒(méi)有中文的，如果我們要顯示中文的話要用第三方的庫(kù)，我這邊下載了一個(gè)帶中文的字庫(kù)wqy-zenhei.ttf（文泉驛正黑）。

示例代碼：

#-*- coding:utf-8 -*-  
import spidev as SPI
import SSD1306
import time

# import sys
# reload(sys)
# sys.setdefaultencoding('utf-8')

from PIL import Image,ImageDraw,ImageFont
 
# Raspberry Pi pin configuration:
RST = 19
DC = 16
bus = 0 
device = 0 

# 128x64 display with hardware SPI:
disp = SSD1306.SSD1306(RST, DC, SPI.SpiDev(bus, device))

# Initialize library.
disp.begin()
 
# Clear display.
disp.clear()
disp.display()

# Create blank image for drawing.
# Make sure to create image with mode '1' for 1-bit color.
width = disp.width
height = disp.height
image = Image.new('1', (width, height))
 
# Get drawing object to draw on image.
draw = ImageDraw.Draw(image)
 
# Draw a black filled box to clear the image.
draw.rectangle((0,0,width,height), outline=0, fill=0)
 
# Draw some shapes.
# First define some constants to allow easy resizing of shapes.
padding = 2
shape_width = 20
top = padding
bottom = height-padding
# Move left to right keeping track of the current x position for drawing shapes.
x = padding
# Draw an ellipse.
draw.ellipse((x, top , x+shape_width, bottom), outline=255, fill=0)
x += shape_width+padding
# Draw a rectangle.
draw.rectangle((x, top, x+shape_width, bottom), outline=255, fill=0)
x += shape_width+padding
# Draw a triangle.
draw.polygon([(x, bottom), (x+shape_width/2, top), (x+shape_width, bottom)], outline=255, fill=0)
x += shape_width+padding
# Draw an X.
draw.line((x, bottom, x+shape_width, top), fill=255)
draw.line((x, top, x+shape_width, bottom), fill=255)
x += shape_width+padding
 
# Load default font.
# font = ImageFont.load_default()
# 使用wqy-zenhei.ttf字庫(kù)，字號(hào)設(shè)置為16，字庫(kù)需要自己下載并放到同一目錄下，如果不在同一目錄下需要指定路徑。字庫(kù)下載推薦：https://www.dafont.com/bitmap.php
font = ImageFont.truetype('wqy-zenhei.ttf', 16)  

# Write two lines of text.
draw.text((x, top),    'Hello',  font=font, fill=255)
draw.text((x, top+20), '你好', font=font, fill=255)
# txt2lcd('星期',x,top+40)

# Display image.
disp.image(image)
disp.display()

運(yùn)行結(jié)果：

注意：運(yùn)行該代碼要用python3版本,用1和2運(yùn)行都會(huì)報(bào)錯(cuò)。還有，python3有一點(diǎn)不同的是，空格和tab是不一樣的，如果你前面用的是tab，后面就要全部統(tǒng)一，否則會(huì)報(bào)錯(cuò)。

2、顯示圖片

1）首先要準(zhǔn)備一張2:1的圖片

為什么是2:1呢？因?yàn)槲矣玫?.96寸的oled屏是2:1的。

2）編輯圖片，把分辨率調(diào)節(jié)為128*64并另存為單色位圖的bmp格式

因?yàn)槲矣玫?.96寸的oled屏分辨率就是128*64的，而且每個(gè)像素點(diǎn)的顏色都是是固定的

3）編寫(xiě)代碼

示例代碼1：

# Copyright (c) 2015 WaveShare
# Author: My MX
import time

import spidev as SPI
import SSD1306

# import Image
from PIL import Image

# Raspberry Pi pin configuration:
RST = 19
DC = 16
bus = 0
device = 0


# 128x32 display with hardware I2C:
disp = SSD1306.SSD1306(rst=RST,dc=DC,spi=SPI.SpiDev(bus,device))

# Initialize library.
disp.begin()

# Clear display.
disp.clear()
disp.display()

# Load image based on OLED display height.  Note that image is converted to 1 bit color.
image = Image.open('test.bmp').convert('1') # 加載  

# Alternatively load a different format image, resize it, and convert to 1 bit color.
#image = Image.open('happycat.png').resize((disp.width, disp.height), Image.ANTIALIAS).convert('1')

# Display image.
disp.image(image)
disp.display()

4）運(yùn)行代碼

注意：圖片的名稱(chēng)和代碼寫(xiě)的要一致，要把做好的圖片和代碼放在同一目錄下，如果不在同一目錄，需要指明圖片的路徑。

運(yùn)行結(jié)果：

PS：實(shí)際效果要好一些，拍出來(lái)有色差

示例代碼2：

顯示一張ppm格式的圖片

import time

import spidev as SPI
import SSD1306

from PIL import Image

# Raspberry Pi pin configuration:
RST = 19
DC = 16
bus = 0
device = 0

# 128x32 display with hardware I2C:
disp = SSD1306.SSD1306(rst=RST,dc=DC,spi=SPI.SpiDev(bus,device))

# Initialize library.
disp.begin()

# Clear display.
disp.clear()
disp.display()

# Load image based on OLED display height.  Note that image is converted to 1 bit color.
image = Image.open('happycat.ppm').convert('1')

# Alternatively load a different format image, resize it, and convert to 1 bit color.
#image = Image.open('happycat.png').resize((disp.width, disp.height), Image.ANTIALIAS).convert('1')

# Display image.
disp.image(image)
disp.display()

運(yùn)行結(jié)果：

五、結(jié)束語(yǔ)

總的來(lái)說(shuō)，在應(yīng)用層的使用，SPI和IIC差不多，都是直接調(diào)用api接口即可，只是用的庫(kù)函數(shù)不一樣，并不需要管底層的通訊是怎樣實(shí)現(xiàn)的。

好了，這一講的內(nèi)容就這么多了，如果對(duì)你有幫助，可以給個(gè)收藏，如果想了解更多樹(shù)莓派的知識(shí)可以關(guān)注我，后續(xù)我會(huì)繼續(xù)更新更多的教程。

教程相關(guān)的軟件和源碼：https://pan.baidu.com/s/1-lVAZyH2s-VTn5qeSnEPhA ，提取碼：qwer