PID, peltier, python logging

hi there,

i'm trying real-time log 2 peltier-temperatures in python. works ok except adc converting errors (see attached picture) every , then. i'm pretty sure it's not python code, here arduino code:

code: [select]

#include <math.h>
#include <pid_v1.h>

int peltier_cold = 2;
int peltier_hot = 3;

float b_value = 3947.7;
float res_25 = 83000;
float temp_25 = 298.15;
float vcc = 5.04;

double setpoint_cold, input_cold, output_cold;
double setpoint_hot, input_hot, output_hot;

//specify links , initial tuning parameters
double conskp_cold=14;
double conski_cold=5;
double conskd_cold=0.8;
pid mypid_cold(&input_cold, &output_cold, &setpoint_cold, conskp_cold, conski_cold, conskd_cold, direct);

double conskp_hot=1;
double conski_hot=3;
double conskd_hot=0.25;
pid mypid_hot(&input_hot, &output_hot, &setpoint_hot, conskp_hot, conski_hot, conskd_hot, direct);

void setup()
{
 // initialize serial communication @ 9600 bits per second:
 serial.begin(115200);

 // initialize pid
 input_cold = read_temperature_cold(); // a0
 setpoint_cold = 18;
 // turn pid on
 mypid_cold.setmode(automatic);
 mypid_cold.setcontrollerdirection(reverse);

 input_hot = read_temperature_hot(); // a1
 setpoint_hot = 28;
 // turn pid on
 mypid_hot.setmode(automatic);
 mypid_hot.setcontrollerdirection(direct);
}

float convert_to_temperature(int sensor_value)
{
 // convert analog reading (which goes 0 - 1023) voltage (0 - 5v):
 float voltage_adc = sensor_value * (vcc / 1023.0);
 // calculate resistance of ntc
 float res_ntc = 100000 * ( vcc/voltage_adc - 1 );
 // calculate temperature
 double temperature_kelvin = 1 / ( ( (log(res_ntc/res_25))/b_value) + (1/temp_25) );
 // convert celsius
 double temperature = temperature_kelvin - 273.15;

 return temperature;
}


float read_temperature_cold()
{
 // read input on analog pin 0:
 int sensor_value_cold = analogread(a0);
 return convert_to_temperature(sensor_value_cold);
}


float read_temperature_hot()
{
 int sensor_value_hot = analogread(a1);
 return convert_to_temperature(sensor_value_hot);
}

void loop()
{
 // --------------------- serial monitoring ---------------
 input_cold = read_temperature_cold();
 input_hot = read_temperature_hot();
 
 //  //serial.print("(c:");
 serial.print(input_cold);
 serial.print(" ");
 serial.print(input_hot);
 serial.print("\n");
 
 // --------------------- pid_1 (cold) ---------------------------
 mypid_cold.settunings(conskp_cold, conski_cold, conskd_cold);
 mypid_cold.compute();
 analogwrite(peltier_cold,output_cold);


 // --------------------- pid_2 (hot) ----------------------------
 mypid_hot.settunings(conskp_hot, conski_hot, conskd_hot);
 mypid_hot.compute();
 analogwrite(peltier_hot,output_hot);

 delay(200);
}


edit: actually, have question well: real-time monitoring lagging quite bit without delay(200) , i'm not quite sure why. adds dead time control loop why rid of it. it's not "real-time" be. it's still has noticeable latency...does have idea why (randomly chosen) 200ms work better or how determine better value?

have tried looking @ serial port data using arduino ide serial port monitor?  why using such high baud rate?

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