Temperature sensor /w Raspberry Pi 3

Question

I am trying to make an temperature sensor.The problem is:I connected the sensor (VCC at 5v , GND at Ground and OUT at the advanced use (that is for the sensor I guess). Now the problem is, i made the python file for it to work , but instead of the real temperature and the voltage it shows me -50 continuously , even if I try to heat him still -50.This is the python code:

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

def readadc(adcnum):
    if ((adcnum > 7) or (adcnum < 0)):
        return -1
    r = spi.xfer2([1,(8+adcnum)<<4,0])
    adcout = ((r[1]&3) << 8) + r[2]
    return adcout

while True:
    for adcInput in range(0,8):
        value = readadc(adcInput)
        voltage = value * 3.3
        voltage /= 1024.0
        tempCelsius = (voltage-0.5)*100
        print "---------------------------"
        print "ADC(", adcInput,")= ", value
        print "---------------------------"
        print "Voltage: ", voltage
        print "---------------------------"
        print "Temp: ", tempCelsius
    time.sleep(1)

Now the thing is , what could possibly cause this problem;the setup of the sensor or the code ? I put the #coding UTF-8 and still -50.I am new in coding and I really can't find how to fix it.

PS : I am using Raspberry Pi 3 2015

Answer 1

You said you connected OUT to pin 28. As I see in your code you are using an ADC interfaced with SPI. SPI is Synchronous, you only connect an OUT digital PIN : a Clock pin misses.

Do you have such shield (ADC with SPI interface)? It is mandatory to have your raspberry reading some analog values (no adc on raspberry).

Answer 2

In fact, it is not possible to read the analog input in the raspberry pi, and you need to use the electronic circuitry to read the information. for example, The MCP3008 is a low cost 8-channel 10-bit analog to digital converter. https://learn.adafruit.com/raspberry-pi-analog-to-digital-converters/mcp3008 and https://learn.adafruit.com/raspberry-pi-analog-to-digital-converters/overview

Answer 3

You're trying to read an analog signal from the Pi - as another use said: this is not possible without an ADC. I recommend using an Arduino board and reading the values from the Arduino via the serial port. Arduino has a vast database for analog signal processing, so I always recommend it first. I wrote a blog article on how to do this, check it out (if you're interested):

Datalogging with Arduino and pySerial on a Raspberry Pi