python - Arduino to Raspberry Pi serial communication creates only random chars after a few seconds -


for project need raspberry pi communicate several peripheral components, 2 of them arduinos. 1 causes problem pro mini 3.3 v atmega328. arduino receives input 2 sensors , transfer data raspberry pi via serial. python code serial-package used on raspberry establishes connection every 50 ms.

when input raspberry printed, first few lines correct after two, 3 seconds printed lines random chars.

my python code looks this:

import serial ser = serial.serial('/dev/ttys0', 115200, timeout=1) if ser.isopen():     ser.close()  ser.open()  ...  # loop try:         ser.write("1")                     ser_line = ser.readline()         print ser_line ...

the arduino code:

#include <wire.h> #include "sparkfunhtu21d.h" #include <fdc1004.h>  fdc1004 fdc(fdc1004_400hz); htu21d myhumidity;  int capdac = 0;  void setup() {     wire.begin();     serial.begin(115200);     myhumidity.begin(); }   void loop() {     string datastring = "";      datastring += string(myhumidity.readhumidity());     datastring += "  ";     datastring += string(myhumidity.readtemperature());     datastring += "  ";      (uint8_t = 0; < 4; i++){                 uint8_t measurement = 0;         uint8_t channel = i;          fdc.configuremeasurementsingle(measurement, channel, capdac);         fdc.triggersinglemeasurement(measurement, fdc1004_400hz);         //wait completion         delay(15);          uint16_t value[2];         if (! fdc.readmeasurement(measurement, value)) {             int16_t msb = (int16_t) value[0];             int32_t capacitance = ((int32_t) 457) * ((int32_t) msb);               capacitance /= 1000; //in femtofarads             capacitance += ((int32_t) 3028) * ((int32_t) capdac);              datastring += string(capacitance);             datastring += "  ";              int16_t upper_bound = 0x4000;             int16_t lower_bound = -1 * upper_bound;              if (msb > upper_bound) {                 if (capdac < fdc1004_capdac_max)                      capdac++;              } else if (msb < lower_bound && capdac > 0) {                 capdac--;                         }         }     }      serial.println(datastring);         delay(20);        // delay in between reads stability }

the output of loop looks like:

print output

so output loses accuracy , become random chars after 6 lines , output doesn't recover. when print serial output in arduino's serial monitor output stays correct time. after several tests run out of ideas. has solution problem or experienced similar behavior?


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