(Circuit Schematic and Code at the end)
Hello!
My group is trying to build a sensor that will (eventually) take differential temperatures between inside and outside containers indoors. I'm doing my best to find and tweak an Arduino code that will read the temperature from our schematic but I keep running into the same error regardless what code I use. Whenever I run the code, the temperature always reads 273.15 C, 459 F, and 0 K. I'm thinking this is due to possibly analog input error but the code is running just fine so maybe not? I tried different beta values and that didn't change the result. I'm truly stumped on what to try next.
Any suggestions?
(also sorry for any formatting errors, this is my first time posting here)
Circuit Schematic (please ignore the note on the side)
//Thermometer with thermistor
/*thermistor parameters:
* RT0: 10 000 Ω
* B: 3977 K +- 0.75%
* T0: 25 C
* +- 5%
*/
//These values are in the datasheet
#define RT0 10000 // Ω
#define B 3977 // K
//--------------------------------------
#define VCC 5 //Supply voltage
#define R 10000 //R=10KΩ
//Variables
float RT, VR, ln, TX, T0, VRT;
void setup() {
Serial.begin(9600);
T0 = 25 + 273.15; //Temperature T0 from datasheet, conversion from Celsius to kelvin
}
void loop() {
VRT = analogRead(A0); //Acquisition analog value of VRT
VRT = (5.00 / 1023.00) * VRT; //Conversion to voltage
VR = VCC - VRT;
RT = VRT / (VR / R); //Resistance of RT
ln = log(RT / RT0);
TX = (1 / ((ln / B) + (1 / T0))); //Temperature from thermistor
TX = TX - 273.15; //Conversion to Celsius
Serial.print("Temperature:");
Serial.print("\t");
Serial.print(TX);
Serial.print("C\t\t");
Serial.print(TX + 273.15); //Conversion to Kelvin
Serial.print("K\t\t");
Serial.print((TX * 1.8) + 32); //Conversion to Fahrenheit
Serial.println("F");
delay(500);
}
gcjr
May 6, 2022, 10:09am
2
is there something wrong with your math
0 x 0.000 VRT 5.000 VR 0.000 RT -inf ln -273.150 TX
32 x 0.156 VRT 4.844 VR 322.906 RT -3.433 ln 128.326 TX
64 x 0.313 VRT 4.687 VR 667.362 RT -2.707 ln 100.912 TX
96 x 0.469 VRT 4.531 VR 1035.599 RT -2.268 ln 86.066 TX
128 x 0.626 VRT 4.374 VR 1430.167 RT -1.945 ln 75.889 TX
160 x 0.782 VRT 4.218 VR 1853.998 RT -1.685 ln 68.116 TX
192 x 0.938 VRT 4.062 VR 2310.469 RT -1.465 ln 61.789 TX
224 x 1.095 VRT 3.905 VR 2803.504 RT -1.272 ln 56.421 TX
256 x 1.251 VRT 3.749 VR 3337.679 RT -1.097 ln 51.725 TX
288 x 1.408 VRT 3.592 VR 3918.367 RT -0.937 ln 47.524 TX
320 x 1.564 VRT 3.436 VR 4551.920 RT -0.787 ln 43.695 TX
352 x 1.720 VRT 3.280 VR 5245.902 RT -0.645 ln 40.153 TX
384 x 1.877 VRT 3.123 VR 6009.390 RT -0.509 ln 36.835 TX
416 x 2.033 VRT 2.967 VR 6853.377 RT -0.378 ln 33.692 TX
448 x 2.190 VRT 2.810 VR 7791.305 RT -0.250 ln 30.685 TX
480 x 2.346 VRT 2.654 VR 8839.778 RT -0.123 ln 27.782 TX
512 x 2.502 VRT 2.498 VR 10019.569 RT 0.002 ln 24.956 TX
544 x 2.659 VRT 2.341 VR 11356.994 RT 0.127 ln 22.183 TX
576 x 2.815 VRT 2.185 VR 12885.905 RT 0.254 ln 19.438 TX
608 x 2.972 VRT 2.028 VR 14650.603 RT 0.382 ln 16.701 TX
640 x 3.128 VRT 1.872 VR 16710.184 RT 0.513 ln 13.949 TX
672 x 3.284 VRT 1.716 VR 19145.299 RT 0.649 ln 11.157 TX
704 x 3.441 VRT 1.559 VR 22068.967 RT 0.792 ln 8.298 TX
736 x 3.597 VRT 1.403 VR 25644.598 RT 0.942 ln 5.338 TX
768 x 3.754 VRT 1.246 VR 30117.648 RT 1.103 ln 2.238 TX
800 x 3.910 VRT 1.090 VR 35874.445 RT 1.277 ln -1.058 TX
832 x 4.066 VRT 0.934 VR 43560.203 RT 1.472 ln -4.624 TX
864 x 4.223 VRT 0.777 VR 54339.605 RT 1.693 ln -8.574 TX
896 x 4.379 VRT 0.621 VR 70551.195 RT 1.954 ln -13.091 TX
928 x 4.536 VRT 0.464 VR 97684.203 RT 2.279 ln -18.509 TX
960 x 4.692 VRT 0.308 VR 152380.844 RT 2.724 ln -25.558 TX
992 x 4.848 VRT 0.152 VR 320000.312 RT 3.466 ln -36.489 TX
1024 x 5.005 VRT -0.005 VR -10240010.000 RT -nan ln -nan TX
#include <stdio.h>
#include <math.h>
//Thermometer with thermistor
/*thermistor parameters:
* RT0: 10 000 Ω
* B: 3977 K +- 0.75%
* T0: 25 C
* +- 5%
*/
//These values are in the datasheet
#define RT0 10000 // Ω
#define B 3977 // K
//--------------------------------------
#define VCC 5 //Supply voltage
#define R 10000 //R=10KΩ
//Variables
float RT, VR, ln, TX, T0, VRT;
void setup() {
#if 0
Serial.begin(9600);
#endif
T0 = 25 + 273.15; //Temperature T0 from datasheet, conversion from Celsius to kelvin
}
#if 0
void loop() {
VRT = analogRead(A0); //Acquisition analog value of VRT
VRT = (5.00 / 1023.00) * VRT; //Conversion to voltage
VR = VCC - VRT;
RT = VRT / (VR / R); //Resistance of RT
ln = log(RT / RT0);
TX = (1 / ((ln / B) + (1 / T0))); //Temperature from thermistor
TX = TX - 273.15; //Conversion to Celsius
Serial.print("Temperature:");
Serial.print("\t");
Serial.print(TX);
Serial.print("C\t\t");
Serial.print(TX + 273.15); //Conversion to Kelvin
Serial.print("K\t\t");
Serial.print((TX * 1.8) + 32); //Conversion to Fahrenheit
Serial.println("F");
delay(500);
}
#endif
void
calc (
int x )
{
VRT = (5.00 / 1023.00) * x; //Conversion to voltage
VR = VCC - VRT;
RT = VRT / (VR / R); //Resistance of RT
ln = log(RT / RT0);
TX = (1 / ((ln / B) + (1 / T0))); //Temperature from thermistor
TX = TX - 273.15; //Conversion to Celsius
printf (" %9d x", x);
printf (" %6.3f VRT", VRT);
printf (" %6.3f VR", VR);
printf (" %12.3f RT", RT);
printf (" %8.3f ln", ln);
printf (" %8.3f TX", TX);
printf ("\n");
}
int main ()
{
setup ();
for (unsigned i = 0; i <= 1024; i += 32)
calc (i);
return 0;
}
I don't think so?... The numbers you posted look about right, I think.
Is the source volts exactly 5V? Makes a difference in calculations.
pidge_gunderson:
T0 = 25 + 273.15;
Mixed data type math without type casting such as ints and floats do not always result in the expected answer. A 25 is different that a 25.0.
Again mixed data type math does not always result in the expected answer. VRT needs to be cast as float or do all the math as ints.
Put a 103 ceramic cap into the Aref pin and ground.
Use a filter of some sort. I recommend SimpleKalmanFilter - Arduino Reference . An example of use.
void fReadBattery( void * parameter )
{
float adcValue = 0.0f;
const float r1 = 50500.0f; // R1 in ohm, 50K
const float r2 = 10000.0f; // R2 in ohm, 10k potentiometer
float Vbatt = 0.0f;
int printCount = 0;
float vRefScale = (3.3f / 4096.0f) * ((r1 + r2) / r2);
uint64_t TimePastKalman = esp_timer_get_time(); // used by the Kalman filter UpdateProcessNoise, time since last kalman calculation
SimpleKalmanFilter KF_ADC_b( 1.0f, 1.0f, .01f );
TickType_t xLastWakeTime = xTaskGetTickCount();
const TickType_t xFrequency = 1000; //delay for mS
for (;;)
{
adc1_get_raw(ADC1_CHANNEL_0); //read and discard
adcValue = float( adc1_get_raw(ADC1_CHANNEL_0) ); //take a raw ADC reading
KF_ADC_b.setProcessNoise( (esp_timer_get_time() - TimePastKalman) / 1000000.0f ); //get time, in microsecods, since last readings
adcValue = KF_ADC_b.updateEstimate( adcValue ); // apply simple Kalman filter
Vbatt = adcValue * vRefScale;
xSemaphoreTake( sema_CalculatedVoltage, portMAX_DELAY );
CalculatedVoltage = Vbatt;
xSemaphoreGive( sema_CalculatedVoltage );
printCount++;
if ( printCount == 3 )
{
//log_i( "Vbatt %f", Vbatt );
printCount = 0;
}
TimePastKalman = esp_timer_get_time(); // time of update complete
xLastWakeTime = xTaskGetTickCount();
vTaskDelayUntil( &xLastWakeTime, xFrequency );
//log_i( "fReadBattery %d", uxTaskGetStackHighWaterMark( NULL ) );
}
vTaskDelete( NULL );
}
Also, take 2 ADC readings throwing away the first one for better results.
This occurs when the analog input reads 1023 causing RT to become inf creating problems with subsequent calculations.
I think the best solution to prevent the issue is to use:
VRT = (5.00 / 1024.00) * VRT; //Conversion to voltage
I changed all the variables to int and I got -274 C, -0.85 K, -461 F. I changed voltage conversion to 5/1024 but that didn't have any affect either. Regardless of these changes, whenever I try to heat up the area around the thermistor it stays constant so I'm wondering if it's an issue with my analog pin? Here's a picture of the physical circuit as well.
Where is the power to the breadboard?
Look at the Blue wire on the breadboard, it does not connect to ground, signal, or power.
See the + of the breadboard?
see the wire going from the breadboard + to the 5V of the Uno?
i don't have anything connected from the + to 5V. I have a black wire from my breadboard ground going to the arduino ground. Is that what you're referencing?
The components on the breadboard do they require power for operation?
yes -- when the circuit isn't connected to the arduino/laptop, I used 9V batteries to power it up
From the Uno there are 2 wires. The ground and the signal wire. How does power get from the Uno to the breadboard?
So I plugged blue wire into 5V in arduino - changed VCC 5 to VCC 9 in code and left variables back in float. Turns out it was a power source issue.
It is a power source issue but i nearly fried my op amp with what i tried so back to drawing board
Weird.
Here's a test of your code from reply #1 ...
VRT = (5.00 / 1023.00) * VRT; //Conversion to voltage
ADC: 995
RT: 355357.46
Temperature:
-37.96C
235.19K
-36.32F
ADC: 996
RT: 368889.25
Temperature:
-38.47C
234.68K
-37.25F
ADC: 997
RT: 383461.90
Temperature:
-39.01C
234.14K
-38.22F
ADC: 998
RT: 399200.37
Temperature:
-39.56C
233.59K
-39.21F
ADC: 999
RT: 416250.40
Temperature:
-40.14C
233.01K
-40.24F
ADC: 1000
RT: 434783.03
Temperature:
-40.73C
232.42K
-41.31F
ADC: 1001
RT: 455000.46
Temperature:
-41.34C
231.81K
-42.42F
ADC: 1002
RT: 477143.34
Temperature:
-41.98C
231.17K
-43.57F
ADC: 1003
RT: 501500.50
Temperature:
-42.65C
230.50K
-44.77F
ADC: 1004
RT: 528421.56
Temperature:
-43.35C
229.80K
-46.03F
ADC: 1005
RT: 558333.87
Temperature:
-44.08C
229.07K
-47.34F
ADC: 1006
RT: 591765.31
Temperature:
-44.84C
228.31K
-48.72F
ADC: 1007
RT: 629375.62
Temperature:
-45.65C
227.50K
-50.16F
ADC: 1008
RT: 672000.62
Temperature:
-46.50C
226.65K
-51.69F
ADC: 1009
RT: 720714.93
Temperature:
-47.40C
225.75K
-53.31F
ADC: 1010
RT: 776923.81
Temperature:
-48.36C
224.79K
-55.04F
ADC: 1011
RT: 842500.81
Temperature:
-49.38C
223.77K
-56.88F
ADC: 1012
RT: 920000.93
Temperature:
-50.48C
222.67K
-58.87F
ADC: 1013
RT: 1013001.00
Temperature:
-51.68C
221.47K
-61.02F
ADC: 1014
RT: 1126667.75
Temperature:
-52.98C
220.17K
-63.36F
ADC: 1015
RT: 1268751.25
Temperature:
-54.42C
218.73K
-65.95F
ADC: 1016
RT: 1451429.87
Temperature:
-56.03C
217.12K
-68.85F
ADC: 1017
RT: 1695001.62
Temperature:
-57.85C
215.30K
-72.13F
ADC: 1018
RT: 2036002.00
Temperature:
-59.96C
213.19K
-75.94F
ADC: 1019
RT: 2547502.50
Temperature:
-62.49C
210.66K
-80.49F
ADC: 1020
RT: 3400003.25
Temperature:
-65.67C
207.48K
-86.20F
ADC: 1021
RT: 5105005.00
Temperature:
-69.98C
203.17K
-93.96F
ADC: 1022
RT: 10220010.00
Temperature:
-76.93C
196.22K
-106.48F
ADC: 1023
RT: inf
Temperature:
-273.15C
0.00K
-459.67F
VRT = (5.00 / 1024.00) * VRT; //Conversion to voltage
ADC: 995
RT: 343103.46
Temperature:
-37.47C
235.68K
-35.44F
ADC: 996
RT: 355714.28
Temperature:
-37.97C
235.18K
-36.35F
ADC: 997
RT: 369259.25
Temperature:
-38.49C
234.66K
-37.28F
ADC: 998
RT: 383846.15
Temperature:
-39.02C
234.13K
-38.24F
ADC: 999
RT: 399600.00
Temperature:
-39.58C
233.57K
-39.24F
ADC: 1000
RT: 416666.65
Temperature:
-40.15C
233.00K
-40.27F
ADC: 1001
RT: 435217.37
Temperature:
-40.74C
232.41K
-41.34F
ADC: 1002
RT: 455454.56
Temperature:
-41.36C
231.79K
-42.44F
ADC: 1003
RT: 477619.06
Temperature:
-42.00C
231.15K
-43.60F
ADC: 1004
RT: 502000.00
Temperature:
-42.67C
230.48K
-44.80F
ADC: 1005
RT: 528947.37
Temperature:
-43.36C
229.79K
-46.05F
ADC: 1006
RT: 558888.93
Temperature:
-44.09C
229.06K
-47.36F
ADC: 1007
RT: 592352.93
Temperature:
-44.85C
228.30K
-48.74F
ADC: 1008
RT: 630000.00
Temperature:
-45.66C
227.49K
-50.19F
ADC: 1009
RT: 672666.68
Temperature:
-46.51C
226.64K
-51.72F
ADC: 1010
RT: 721428.56
Temperature:
-47.41C
225.74K
-53.34F
ADC: 1011
RT: 777692.31
Temperature:
-48.37C
224.78K
-55.06F
ADC: 1012
RT: 843333.31
Temperature:
-49.39C
223.76K
-56.91F
ADC: 1013
RT: 920909.12
Temperature:
-50.49C
222.66K
-58.89F
ADC: 1014
RT: 1014000.00
Temperature:
-51.69C
221.46K
-61.04F
ADC: 1015
RT: 1127777.87
Temperature:
-52.99C
220.16K
-63.39F
ADC: 1016
RT: 1270000.00
Temperature:
-54.43C
218.72K
-65.97F
ADC: 1017
RT: 1452857.12
Temperature:
-56.04C
217.11K
-68.87F
ADC: 1018
RT: 1696666.62
Temperature:
-57.86C
215.29K
-72.15F
ADC: 1019
RT: 2038000.00
Temperature:
-59.98C
213.17K
-75.96F
ADC: 1020
RT: 2550000.00
Temperature:
-62.51C
210.64K
-80.51F
ADC: 1021
RT: 3403333.25
Temperature:
-65.68C
207.47K
-86.22F
ADC: 1022
RT: 5110000.00
Temperature:
-69.99C
203.16K
-93.97F
ADC: 1023
RT: 10230000.00
Temperature:
-76.94C
196.21K
-106.50F
so turns out it seems to be more of a power connection issue than a code issue but I did switch to 5/1024 still :))
So I guess the issue is finding a way to get power from arduino to circuit without frying my components. Any ideas? Should I try plugging batteries into circuit while it's plugged into the arduino?
I have to ask, is there a particular reason for using thermistors in this application?
The DS18B20 digital temperature sensors are pretty accurate and a lot easier to use than thermistors.
