Hi all! Thank you in advance for your help.
I am using an Arduino Micro to log data from 12 analog sensors to a micro SD card. When tethered to the computer over USB, the data both prints to the serial monitor and to the SD card fine. I have a forced delay of 10ms, so it logs approximately every 30ms. However, as soon as I plug in the battery and unplug the computer, the data only writes to the card every 10-13 seconds or so. Initially I used an alkaline 9V. My set up draws about 150mA, which should be fine for that type of battery. Suspecting power issues, I also tried a lithium 9V and 6 AA batteries, but it made no difference. I then suspected timing issues with writing to the card, so I played around with implementing different delays both at the end of the code and before I print my data string to the card. This also didn't really have an effect. Finally, I tried to print directly to the card after reading each sensor, rather than forming a data string. This changed my output but didn't solve the problem. Essentially, because I was opening and closing the connection to the SD card 12 times, while tethered the card wrote every 200ms. Once on battery power, that immediately jumped to every 2 seconds. The over all effect isn't as bad as before, but there is still an unexplained jump in time between logs while on battery power.
Here is the code when I form the data string
/*
SD card datalogger
This example shows how to log data from three analog sensors
to an SD card using the SD library.
The circuit:
* analog sensors on analog ins 0, 1, and 2
* SD card attached to SPI bus as follows:
** MOSI - pin 11
** MISO - pin 12
** CLK - pin 13
** CS - pin 4
created 24 Nov 2010
modified 9 Apr 2012
by Tom Igoe
This example code is in the public domain.
*/
#include <SD.h>
// On the Ethernet Shield, CS is pin 4. Note that even if it's not
// used as the CS pin, the hardware CS pin (10 on most Arduino boards,
// 53 on the Mega) must be left as an output or the SD library
// functions will not work.
const int chipSelect = 4;
void setup()
{
// Open serial communications and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for Leonardo only
}
Serial.print("Initializing SD card...");
// make sure that the default chip select pin is set to
// output, even if you don't use it:
pinMode(10, OUTPUT);
// see if the card is present and can be initialized:
if (!SD.begin(chipSelect)) {
Serial.println("Card failed, or not present");
// don't do anything more:
return;
}
Serial.println("card initialized.");
}
void loop()
{
// make a string for assembling the data to log:
String dataString = "";
// read three sensors and append to the string:
for (int analogPin = 0; analogPin < 12; analogPin++) {
int sensor = analogRead(analogPin);
dataString += String(sensor);
if (analogPin < 12) {
dataString += ",";
}
}
unsigned long time;
time = millis();
dataString += time;
// open the file. note that only one file can be open at a time,
// so you have to close this one before opening another.
File dataFile = SD.open("datalog.txt", FILE_WRITE);
// if the file is available, write to it:
if (dataFile) {
dataFile.println(dataString);
dataFile.close();
// print to the serial port too:
Serial.println(dataString);
}
// if the file isn't open, pop up an error:
else {
Serial.println("error opening datalog.txt");
}
delay(10);
}
and here is my implementation of writing to the SD card each read, rather than forming a data string:
#include <SD.h>
// On the Ethernet Shield, CS is pin 4. Note that even if it's not
// used as the CS pin, the hardware CS pin (10 on most Arduino boards,
// 53 on the Mega) must be left as an output or the SD library
// functions will not work.
const int chipSelect = 4;
void setup()
{
// Open serial communications and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for Leonardo only
}
Serial.print("Initializing SD card...");
// make sure that the default chip select pin is set to
// output, even if you don't use it:
pinMode(10, OUTPUT);
// see if the card is present and can be initialized:
if (!SD.begin(chipSelect)) {
Serial.println("Card failed, or not present");
// don't do anything more:
return;
}
Serial.println("card initialized.");
}
void loop()
{
// read sensors and append to the string:
for (int analogPin = 0; analogPin < 12; analogPin++) {
int sensor = analogRead(analogPin);
if (analogPin < 12) {
File dataFile = SD.open("datalog.txt", FILE_WRITE);
dataFile.print(sensor);
dataFile.print(",");
dataFile.close();
}
}
unsigned long time;
time = millis();
File dataFile = SD.open("datalog.txt", FILE_WRITE);
dataFile.println(time);
dataFile.close();
// print to the serial port too:
Serial.println(time);
delay(50);
}
For my application, I'd like to log data very quickly, on the order of every 30ms. Any advice you can give as to why I might be having this problem would be greatly appreciated!