Have you noticed a problem with analogRead?

My analogRead values have been jumping around a bit. Admittedly, this could be due to any number of reasons.  However, I figured Atmel must have put the noise reduction mode in for a reason and thought I'd give it a try first.  But this didn't turn out to be so straightforward with Arduino, so I'm on to looking at my hardware now.

Well, I'm sure a lot of people would find it useful to have a function that reads an analog input using ADC noise reduction, defined as such:

int analogNoiseReducedRead(int pinNumber)

But coding this is beyond my knowledge and skills. Anyone feel like taking it on and posting it here?

Would this work?

Code:

#include <avr/sleep.h>

void setup()
{
  Serial.begin(9600);
}

void loop()
{
  int reading;
  
  reading = analogNoiseReducedRead(0);
  Serial.println();
  delay(500);
}

int analogNoiseReducedRead(int pinNumber)
{
  int reading;
  
  ADCSRA |= _BV( ADIE );             //Set ADC interrupt
  set_sleep_mode(SLEEP_MODE_ADC);    //Set sleep mode
  reading = analogRead(pinNumber);   //Start reading
  sleep_enable();                    //Enable sleep
  do
  {                                  //Loop until reading is completed
    sei();                           //Enable interrupts
    sleep_mode();                    //Go to sleep
    cli();                           //Disable interrupts
  } while(((ADCSRA&(1<<ADSC))!= 0)); //Loop if the interrupt that woke the cpu was something other than the ADC finishing the reading
  sleep_disable();                   //Disable sleep
  ADCSRA &= ~ _BV( ADIE );           //Clear ADC interupt
  sei();                             //Enable interrupts
  
  return(reading);
}

Thanks Coding Badly.  The thread you've linked to is too long and complex for a noob like me.  Where is the analog pin to be read defined? Where is the call made to read it with the ADC?

Can someone please provide code for using ADC Noise Reduction when reading an analog input? Thanks!

I'd definitely be interested to see the results. Thanks Brian!

Hi Brian,
Your code is great, but unfortunately the ATMega168 and ATMega328 (which I believe come with the Arduino Duemilanove, which I have on order) do not have watchdog clock dividers, unlike the AT90USB82 that you are using.

This means that the maximum time between watchdog interrupts for the Arduino Duemilanove is 8 seconds... Bummer!

Looks like the best I can do is what r55boy suggested... waking it up every 8 seconds to increment a counter then putting it back to sleep again... On every n wake ups execute the main code.

Thanks Brian,
I've worked out a new control algorithm that doesn't require date/time, so now I just need to put the arduino to sleep and wake it every few minutes to conserve energy. Looks like the thread you've linked to will do the trick.

Cheers,
Todd

I'm still waiting for my first Arduino in the post, so excuse my ignorance...

I'm looking to use the software real time clock in my first project as I need to trigger a function twice a day at certain times. I'm also looking at using the watchdog timer and sleep functions to save energy (http://interface.khm.de/index.php/lab/experiments/sleep_watchdog_battery/).

Are the two compatible, or is there some way to make them compatible? I realise that I might need to use a different sleep mode than that used in the example linked to above (maybe "power save" mode instead of "power down" mode).

Any help would be appreciated!

You can download a zip file containing all of the relevant files plus an example here:

http://sites.google.com/site/toddsstuffnthat/arduino-code-1/ByteSizedDataLoggerLibrary.zip

Extract the DataLogger folder to ..\hardware\libraries\ in your Arduino directory.

Please let me know if you end up using it.

Hi Nachtwind,
As it stands it only uses built-in EEPROM, but I'm sure it could be adapted. Being very new to all of this I'm not really sure how easy or difficult it would be to do so.

Personally I don't have much need for more memory. I'm using an ATMega328, which (I am led to believe) has 1024 bytes of EEPROM available. So, it can fit 40 days worth of 1-hour time step data for one variable, which is plenty for my application.

I will post some files in the next few days if people are interested.

[.AddVariable(int Size, Int Cycle):]

I have just finished building a byte-sized (literally & figuratively) DataLogger library for EEPROM data storage and retrieval. It includes the following functions:

• .AddVariable(int Size, Int Cycle): Adds variables to the data logger of a given size and cycle*
  
• .Write(int VarNum, int Value): Stores a value for a given variable
  
• .Read(int VarNum, int ValNum): Retrieves a value for a given variable
  
• .Encode(float Value, float Min, float Max): Encodes (scales between Min and Max) a value into 1-byte ready for storage
  
• .Decode(int Value, float Min, float Max):  (The inverse to encode) Decodes a retrieved value, ready for use
  
• .Export(): Writes all data to the serial port in CSV format for easy copy-and-pasting from the serial monitor into a spreadsheet for analysis (columns = variables, rows = values).
  
• Additional functions for retrieving specific information about the DataLogger and its variables; for clearing values from one or all variables; for initialising a variable of the DataLogger class type.

* A variable being cycled (Cycle ==1) means that values are progressively overwritten once the variable's memory block is full. (Cycle == 0 [ch8594] not cycled)


Would others find this useful? If so, let me know and I will document and post it.

You're right, processing time for a division by 4 is no big deal for my application. Thanks.

I'd like to change the ADC resolution to 8-bit. I am using a Duemilanove with ATMega328.

I understand that the default resolution of the Ardiunio's analog inputs is 10-bits (1024 levels). I am storing analog values as single bytes in EEPROM, so the additional 2-bits of resolution is unnecessary. I could mathematically convert 10-bit to 8-bit and then store, but thought it would be more efficient to just reduce the ADC resolution to 8-bit (1 byte) if possible.

Does anyone know how to do this?

What is the easiest way to add more memory to an Arduino Duemilanove (above the 512 bytes EEPROM available)?