External EEPROM - Read code just repeats one record

Other Hardware Storage
1

I'm recording some data to external EEPROM (I2C) in a CSV format.

My sketch to Write seems to work , as indicated by troubleshooting code I added that does a read to Serial Monitor after each write.

But my sketch to Read to Serial Monitor fails b/c repeatedly reads off the same record.

I got the same result with 2 different I2C/EEPROM modules, 2 different Arduinos and with similar code written by two people.

--- Write sketch (with lines to read that I added for troubleshooting) :
result to Ser Mon is rows of CSV with incrementing SampleCounter and values as expected from random()

#include <Wire.h>
#include "SparkFun_External_EEPROM.h" // 
ExternalEEPROM myMem;
String sample2Write = "";     // build up data from one sample
String sampleRead = "";
int sampleSize = 200;  // for demo, each sample= 200 *bits*
int sampleCounter = 1;

void setup() //////////////////////////////////////////
{
  Serial.begin(9600);
  Wire.begin();
  // create and check connect to Ext EEPROM
    if (myMem.begin() == false){
      Serial.println("No memory detected. Freezing.");
      while (1);}
} // setup

void loop(){
  delay(3000);
  sampleCounter++;
  
  // WRITE  ////////////////////////////////////////////////////
  sample2Write = "";
  // sample # and address
    sample2Write = sample2Write + String(" - ") + "," ;  // spacer for SerMon display
    sample2Write = sample2Write + String(sampleCounter) + "," ;  
    sample2Write = sample2Write + String(random(10, 20)) + "," ;
    sample2Write = sample2Write + String(random(21, 30)) + "," ;
  
  // write to external EEPROM
    myMem.put(sampleCounter*sampleSize, sample2Write); //(location, data)

//    READ DATA    /////////////////////////////////////////////
  sampleRead="",
  myMem.get(sampleCounter*sampleSize, sampleRead); // location, receiver var
  Serial.println(sampleRead);
  
} // loop

--- Read sketch: result to Ser Mon is rows of CSV with values but always the same sampleCounter and same data

#include <Wire.h>
#include "SparkFun_External_EEPROM.h" // 
ExternalEEPROM myMem;
String sampleRead = "";
int sampleSize = 200;  // for demo, each sample= 200 *bits*
int sampleCounter = 1;

void setup() //////////////////////////////////////////
{
  Serial.begin(9600);
  Wire.begin();
  if (myMem.begin() == false)
    {
    Serial.println("No memory detected. Freezing.");
    while (1);
    }
} // setup

void loop(){
  delay(3000);
//    READ DATA    /////////////////////////////////////////////
  sampleCounter++;
  sampleRead="",
  myMem.get(sampleCounter*sampleSize, sampleRead); // location, receiver var
  Serial.println(sampleRead);
} // loop
2

Which controller do you use?

What exactly does this method do?
How many bytes are read?

3

Thanks, Dr. Diettrich

Arduino Uno

.get is from the Arduino EEPROM library https://docs.arduino.cc/learn/built-in-libraries/eeprom

I'm writing and reading 200 bits for each sample (set of values = one line in CSV). That is 3 integers of 16 bits each and 8 characters of 8 bits each and some extra room for future (84 bits).

4

No, you don't :frowning:

Reading and writing is done in bytes, not bits, and dynamic data types like String are not supported. Most probably you write a pointer and read it back, so that you happen to log the String still stored in RAM.

5

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