Sometimes we want to store data on the arduino that will survive a reset, calibration settings and set points are an example of this. EEPROM is a non volatile memory on the arduino that we can write values to and read in the setup loop to keep the values after a reset.
There are many blogs that will talk about, writing and reading EEPROM, but not many [if any] talk about checking if the memory slot has ever been written to in the past. We want to be able to use the value of a variable [ie setpoint] from the eeprom if there is one there, if there is not we want to use a defined value from the sketch.
What this code does, it reads the eeprom to see if there is a value to read, if not it ignores the eeprom and substitutes the one from the top of the code.
here is a serial screenshot showing it in action, resetting makes it move onto the next memory slot:
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/* Script to test how to check if eprom is written or not it will start at memory slot 1 and print value if it has ever been written it will then write the next empty slot to the value you put at the top of the code
28/8/2015 Michael Ratcliffe Mike@MichaelRatcliffe.com
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include <EEPROM.h> int backupvalue=512;
int i=1; int value=100;
void setup() { Serial.begin(9600); Serial.print("Arduino Reset button pressed"); while (value>=2) { i++; value = EEPROM.read(i); Serial.print("Memory _Slot:"); Serial.print(i); Serial.print(" has saved value:"); Serial.println(value*4); delay(10);
//We will stop at 100, you must have got the point by now and I dont know what happens if you write a eprom memory slot that is out of range if(i>=100) return; }; value=backupvalue/4; EEPROM.write(i, value);
// turn the LED on when we're done digitalWrite(13, HIGH); }
void loop() { /** Empty loop. **/ } |
Want to clear your EEPROM for your next project, here is the code to do it:
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/* * EEPROM Clear * * Sets all of the bytes of the EEPROM to 0. * Please see eeprom_iteration for a more in depth * look at how to traverse the EEPROM. * * This example code is in the public domain. */
#include <EEPROM.h>
void setup() {
/*** Iterate through each byte of the EEPROM storage.
Larger AVR processors have larger EEPROM sizes, E.g: - Arduno Duemilanove: 512b EEPROM storage. - Arduino Uno: 1kb EEPROM storage. - Arduino Mega: 4kb EEPROM storage.
Rather than hard-coding the length, you should use the pre-provided length function. This will make your code portable to all AVR processors. ***/
for (int i = 0 ; i < EEPROM.length() ; i++) { EEPROM.write(i, 0); }
// turn the LED on when we're done digitalWrite(13, HIGH); }
void loop() { /** Empty loop. **/ } |
This will come in handy in our later projects.
