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書名： Internet of Things Programming with JavaScript
作者名： Rubén Oliva Ramos
本章字?jǐn)?shù)： 365字
更新時(shí)間： 2021-04-02 20:31:20

Raspberry Pi GPIO header

The following screenshot is a chart of the GPIO pins of the Raspberry Pi Zero. In this case, we will use the SPI configuration interface (SPI_MOSI, SPI_MISO, SPI_CLK, SPI_CE0_N):

The following diagram shows the name of the pins of the MCP3008 chip that you connect to the Raspberry Pi:

The following image shows the temperature sensor:

You need to connect the following pins according to the next description:

VDD to 3.3 volts
VREF to 3.3 volts from the Raspberry Pi Zero
Pin AGND to GND
Pin CLK (clock) to GPIO11 of the Raspberry Pi
DOUT to GPIO9
Pin DIN to GPIO10
Pin CS to GPIO8 and the pin
Pin the MCP3008D GND to Ground

This connection is represented in the following figure:

The following image shows the connections of the sensor to the ADC MCP3008 and the Raspberry Pi:

Reading the data with a Python script

In the next section, you will create the MCP3008.py file; you need to follow the next steps:

Open the terminal on your Raspberry Pi Zero.
Enter the interface in your Pi terminal.
It's important to use nano before.
Type sudo nano MCP3008.py.

It will appear on the screen and we will describe the following lines:

Import libraries:

        import spidev1 
        import os1

Open the SPI bus:

        spi1 = spidev1.SpiDev1() 
        spi1.open(0,0)

Define the channels from the ADC MCP2008:

        def ReadChannel1(channel1): 
          adc1 = spi1.xfer2([1,(8+channel1)<<4,0]) 
          data1 = ((adc1[1]&3) << 8) + adc1[2] 
          return data1

The function to convert volts is as follows:

        def volts(data1,places1): 
          volts1 = (data1 * 3.3) / float(1023) 
          volts1 = round(volts1,places1) 
          return volts1

The function to convert temperature is as follows:

        def Temp(data1,places1): 
          temp1 = (data1 * 0.0032)*100 
          temp1 = round(temp1,places1) 
          return temp1

Define channels from the ADC:
```
          channels = 0 
```
Define the reading time:
```
        delay = 10 
```

The function to read the temperature is as follows:

        while True: 
 
          temp  = Channels(temp) 
          volts = Volts(temp1,2) 
          temp  = Temp(temp1,2)

Print the results:

        print"**********************************************" 
        print("Temp : {} ({}V) {} degC".format(temp1,volts,temp))

Wait every 5 seconds:
```
        Time1.sleep(delay) 
```
Run the Python file using the following command:
```
sudo python MCP3008.py
```
On the following screen, we can see the temperature, the ADC measurements, and the volts according to the temperature:

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Internet of Things Programming with JavaScript

Raspberry Pi GPIO header

Reading the data with a Python script