Slow Read External EEPROM 24LC

Using Arduino Programming Questions
#1

Hi All,
This is part of an personal RFID door lock project.
I am using external eeprom Microchip 24LC128 and arduino nano. Comparing it with the built-in eeprom I get much lower reading results. I connected it as shown below:

24LC256 Arduino nano
VCC 5V
GND GND
SCL SCL (A5)
SDA SDA (A4)
Others GND

For the test I use the following sketch:

#include <Wire.h>
#define EEPROM1 0x50

int Counter1=0;
int Counter2=10;
String RFID;
int i=0;
int b=0;

void setup() {
 Wire.begin();
 Serial.begin(9600);
 Serial.println("START");
     while(Counter2<10000){// Прочита всички номера
      for(b=Counter1 ; b < Counter2 ; b++){char f = readEEPROM(EEPROM1, b);RFID += (f);}
      Counter1=Counter1+10;
      Counter2=Counter2+10;
      //Serial.println(RFID); //slows down!
      RFID="";
      if(Counter2>=10000){
        Serial.println("STOP");
      }
    }
}
//---------------------------------------------------------
void loop(void){}
//---------------------------------------------------------
byte readEEPROM(int deviceaddress, unsigned int eeaddress ) 
{
  byte rdata = 0xFF;
  Wire.beginTransmission(deviceaddress);
  Wire.write((int)(eeaddress >> 8));   // MSB
  Wire.write((int)(eeaddress & 0xFF)); // LSB
  Wire.endTransmission();
  Wire.requestFrom(deviceaddress,1);
  if (Wire.available()) rdata = Wire.read();
  return rdata;
}

The result is:
11:55:47.503 -> START
11:55:53.030 -> STOP

5.5sec for 10000bytes / 1000 RFID tags. With the built-in eeprom I achieved a result of 16ms for 1000 bytes, ie for 10000 bytes it should be 160ms. I guess no one will be happy to wait 5-6 seconds until the device decides whether to open the door or not. :slight_smile:
I've also tried an external library such as SparkFun external eeprom but the result is worse.

Is this speed normal for external EEPROM? What can limit the reading speed? Can I improve the speed?

#2

I've this test code using a 24LC256 and RobTillaart's library

#include <I2C_eeprom.h>  // https://github.com/RobTillaart/I2C_EEPROM
I2C_eeprom storage(0x50, I2C_DEVICESIZE_24LC256); // AT24C256 @ 0x50

const uint32_t cardCount = 1000;

bool addressOfCardID(uint32_t cardID, uint32_t& cardAddress) {
  bool foundCard = false;
  uint32_t idBuffer;

  uint32_t t0 = micros();
  for (uint32_t cID = 1, cAdd = 0; cID <= cardCount; cID++, cAdd += sizeof(uint32_t)) {
    storage.readBlock(cAdd, (uint8_t*) &idBuffer, sizeof idBuffer);
    if (idBuffer ==  cardID) {
      cardAddress = cAdd;
      foundCard = true;
      Serial.print((micros() - t0) / 1000.0, 0);
      Serial.print(F(" ms\tto find card #")); Serial.print(cardID);
      Serial.print(F(".\taddress: ")); Serial.println(cardAddress);
      break;
    }
  }
  return foundCard;
}

void setup() {
  Serial.begin(115200);
  Wire.setClock(400000); // 400KHz is fast mode, Max. Clock Freq. for 24LC128 (otherwise use 100KHz (standard mode) )

  storage.begin();
  if (! storage.isConnected()) {
    Serial.println(F("external EEPROM error."));
    while (true) yield();
  }

  // initalize the memory
  for (uint32_t cardID = 1, cardAddress = 0; cardID <= 1000; cardID++, cardAddress += sizeof(uint32_t)) {
      storage.writeBlock(cardAddress, (uint8_t*) &cardID, sizeof(uint32_t));
  }

  uint32_t cardAddress = 0;
  if (! addressOfCardID(1   , cardAddress)) Serial.println(F("No card with ID #1"));    // best case
  if (! addressOfCardID(500 , cardAddress)) Serial.println(F("No card with ID #500"));  // middle point
  if (! addressOfCardID(1000, cardAddress)) Serial.println(F("No card with ID #1000")); // worst case

  // random access
  Serial.println(F("------------------------------"));
  for (uint32_t test = 0; test <= 10; test++) {
    uint32_t cardID = random(1, 1001);
    if (! addressOfCardID(cardID, cardAddress)) {
      Serial.print(F("No card with ID #")); Serial.println(cardID);
    }
  }
}

void loop() {}

that's the output

1 ms	to find card #1.	address: 0
435 ms	to find card #500.	address: 1996
868 ms	to find card #1000.	address: 3996
------------------------------
701 ms	to find card #808.	address: 3228
217 ms	to find card #250.	address: 996
64 ms	to find card #74.	address: 292
572 ms	to find card #659.	address: 2632
808 ms	to find card #931.	address: 3720
237 ms	to find card #273.	address: 1088
473 ms	to find card #545.	address: 2176
763 ms	to find card #879.	address: 3512
802 ms	to find card #924.	address: 3692
616 ms	to find card #710.	address: 2836
383 ms	to find card #441.	address: 1760

so for 1000 cards using 4 bytes for their ID, the worst case scenario (looking at card #1000) is 868 ms.
Less than one second is likely acceptable. of course this is a worst time, if you have a low rank, then that will be faster. if this is still too slow, then a hash strategy on where to store cards based on their ID could be implemented to start searching from a different address. but in my view this is not needed