Simple Handy Phone Thermometer Using Digispark Attiny85

In this tutorial, we are going to build a simple OTG Phone Thermometer using Digispark ATtiny85 that can connect to our mobile phone via an OTG adaptor and read the real-time temperature of anything and display it on the serial monitor.

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How it works!

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Things Required

Components	AliExpress	Banggood
Digispark ATtiny85
10k Precision thermistor
10k Resistor
OTG Adaptor

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Software Required

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Circuit

The connections are very straight forward, follow the below steps.

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Code

Upload the provided code to Digispark attiny85 using the Arduino IDE.

For more info on using Digispark attiny85 with Arduino IDE follow this tutorial

https://www.hackster.io/alaspuresujay/use-an-attiny85-with-arduino-ide-07740c

#include <DigiCDC.h>

// the value of the 'other' resistor
#define SERIESRESISTOR 10000
// What pin to connect the sensor to
#define THERMISTORPIN A1
#define THERMISTORNOMINAL 10000
// temp. for nominal resistance (almost always 25 C)
#define TEMPERATURENOMINAL 25
// how many samples to take and average, more takes longer
// but is more 'smooth'
#define NUMSAMPLES 5
// The beta coefficient of the thermistor (usually 3000-4000)
#define BCOEFFICIENT 3950

void setup() {
  SerialUSB.begin();
}

// the loop routine runs over and over again forever:
void loop()
{
  if (SerialUSB.available())
  {
    uint8_t i;
    float average;
    average = analogRead(THERMISTORPIN);

    // convert the value to resistance
    average = 1023 / average - 1;
    average = SERIESRESISTOR / average;
    //SerialUSB.print("Thermistor resistance ");
    //SerialUSB.println(average);

    float steinhart;
    float presteinhart;
    steinhart = average / THERMISTORNOMINAL;     // (R/Ro)
    steinhart = log(steinhart);                  // ln(R/Ro)
    steinhart /= BCOEFFICIENT;                   // 1/B * ln(R/Ro)
    steinhart += 1.0 / (TEMPERATURENOMINAL + 273.15); // + (1/To)
    steinhart = 1.0 / steinhart;                 // Invert
    steinhart -= 273.15;                         // convert absolute temp to C

    if (int(presteinhart) != int(steinhart))
    {
      SerialUSB.print("Temperature ");
      SerialUSB.print(steinhart);
      SerialUSB.println(" *C");
      presteinhart = steinhart;
    }
    SerialUSB.delay(1000);
  }
}

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In Action!!!

Now it time to test our phone thermometer, follow the below steps carefully.

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In the below video I’m checking the temperature of a cup of tea. ENJOY!