Here's the schematics of my NTC - ADC circuit,
ADC 10bits, ADCVCC 2.56V
Vin = 5V
Someone can explain me how i get RT, the value of resistance of NTC from ADC value? thanks.
I'm using the voltage divider formula:
Vout = ADCVCC * ADC_value / 1024 BETA = 3950 R25 = 4700 RT = 10K / (Vin - Vout - 1) T = (1 / (1/298.16 + 1/BETA * ln(RT/R25 )) - 273.15
But I got wrong results:
the range of my temperatures are:
adc = 1 -> T = 344 °C; adc = 1023 -> T = 8
How I have to set up the ADC in AVR? with internal voltage reference or not?
do i have wrong formula?
I need to read "exact" temperature in range of -10°C to +30°C more or less.
I've tried already with SH equation with coefficent A,B,C but i've got worst results!!!
I think I've don't understand the schematics of NTC - ADC circuits...
And set up my ATMega with wrong parameters.
Someone can try to explain me how to convert my ADC value to Resistence of thermistor with this schematics?
Thanks in advice for help.
My setup for AVR ADC:
ADMUX |= (1<<REFS0) | (1<<REFS1); ADCSRA |= (1<<ADEN) |(1<<ADSC) |(1<<ADIE); ADCSRA |= (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0);
and the formula used to get Resistance from ADC value: Vin = 5V Vref = 2,56V (AREF)
Vout = adc_val * (Vref / 1024.0)) RT = 10k / (Vin / Vout - 1.0)
This code match the schematics? Is it correct my ADC set up with those schematics? thanks in advice.