10. Grayscale Sensor

This sensor is used to detect the light density and reflect the analog voltage signal back. So it can be used to detect black and white colors. Below is an example of some material light density.

Warning

Before proceeding with this sensor, you will need to learn about the MCP3008 ADC.

10.1. Connecting the Sensor

The grayscale sensor is an analog sensor and cannot be connected directly to the Raspberry Pi pins. It needs an analog to digital converter, MCP3008 ADC in this case, in order to collect proper data.

10.2. Python Program to Get Readings

import spidev
import time

delay = 0.5
ldr_channel = 0

spi = spidev.SpiDev()
spi.open(0,0)

def readadc(num):
    if adcnum > 7 or adcnum < 0:
        return -1
    r = spi.xfer([1, 8+adcnum << 4, 0])
    data = ((r[1]&3)<<8 + r[2])
    return data

while True:

    Sum=0
    Sum2=0
    ldr_value=readadc(0)
    
    if ldr_value != 0:
        result = ldr_value/1024;
        Sum=Sum+10
        
        while result != (ldr_value%1023):
            result = result/1024
            Sum = Sum + 10
            if Sum > 1024:
                break
            
        result = ldr_value%1023
        while result != 1:
            result = result/2
            Sum2 = Sum2 + 1
            if Sum2 > 1024:
                break

        result = ((Sum + Sum2)/1024.0)

        if result > 0.1:
            print 'Black'
        else:
            print 'White'
            
        time.sleep(delay)