Can't properly flash Attiny85, please help.

I have working proto of a bathroom exhaust fan controlled by methane sensor via arduino uno. I now wish to transfer this sketch to an ATtiny85 (cause i had extras). I have programmed ATtiny before, and can successfully get 'blink' going on this specific MCU. However I cannot get my sensor sketch to work properly... Perhaps I am asking too much of this little guy? I am including my code and video in hopes that someone can steer me in the right direction. 

  AT85      Arduino    Circuit
  0 (PB5)   A0             pin 3 of 50k pot
  2 (PB7)   ~9             led or relay
  Trim Pot     
  1              GND
  2              GND
  3              Arduino (attiny) & Sensor B1
  A1             +5VDC
  H1             GND
  GND            GND
  B1             Trim Pot 3

const int numReadings = 10;    // average sensor reading used from 10 samples

int ledPin = 1;                  // replaced ac/dc relay with led to debug
int readings[numReadings];      // the readings from the analog input
int index = 0;                  // the index of the current reading
int total = 0;                  // the running total
int average = 0;                // the average

int inputPin = 0;    //reading from sensor

unsigned long start_time;
unsigned long current_time;
unsigned long elapsed_time;

void setup()
  // sets digital pin 1 to output
  pinMode(ledPin, OUTPUT);
  // sets analog 0 to input
  pinMode(inputPin, INPUT);
  // initialize all the readings to 0:
  for (int thisReading = 0; thisReading < numReadings; thisReading++)
    readings[thisReading] = 0;         


void loop() {
  // 10 sample average used to prevent false positive from a bounce and/or spike
  // subtract the last reading:
  total= total - readings[index];        
  // read from the sensor: 
  readings[index] = analogRead(inputPin);
  // add the reading to the total:
  total= total + readings[index];      
  // advance to the next position in the array: 
  index = index + 1;                   

  // if we're at the end of the array...
  if (index >= numReadings)             
    // ...wrap around to the beginning:
    index = 0;                          

  // calculate the average:
  average = total / numReadings;        
  // send it to the computer as ASCII digits
     delay(1000); // delay in between reads for stability           
  int threshold = 300;                  // sets the threshold value
  if(average > threshold){  // determines if the level of methane breaks threshold
    start_time = millis();      // starts exhaust fan on 5 min timer
    digitalWrite(ledPin, HIGH); 
    do  {
      current_time = millis();      // defines the 5 minute timer
      elapsed_time = current_time - start_time;
    while(elapsed_time < 300000); // 5 min. countdown
    if(average < threshold){      // sensor is checked against threshold
      digitalWrite(ledPin, LOW);  // fan turns off if sensor value below threshold
    }                             // or stays on until it is below threshold

thanks in advance!

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Here's the fast snippet. It uses something called an exponential forgetter or zero order hold.

The maths is

Current result = last result x forgetterconstant +(current result *(1-forgetterconstant)

Where 0
The code does this with constants based on multiples of 2, so multiply and divides are all done by binary shift operations.

//Val is the current number read from the ADC
//LastVal is the previous ADC number

#define tmfilt 15

Val = analogRead(analogPin);
//Apply an exponential forgetter
LastVal = (LastVal*tmfilt) + (Val<<4) >>4;
//LastVal has filtered number in it
//Now scale to 0..100
LastVal = (LastVal*100)>>10 ;
earthtown (author)  steveastrouk4 years ago
Awesome, I'll give her a whirl. Thanks for the help steveastrouk.
The code should fit, but there are faster ways of implementing the kind of filter you have there. I have a piece of Arduino code that's very short and compact, I'll have to dig it out.
earthtown (author)  steveastrouk5 years ago
That would be great, thanks.
Have you definitely got the correct target set in the ide ?
earthtown (author)  steveastrouk5 years ago
The pinout in the top of the code is incorrect, the ATtiny85 should be PB0 to led/relay and PB1 to potpin 3.

I had the sensor wired incorrectly it turns out.

I haven't tested the tiny again since realizing this...but as far as you can tell have I exceeded the limitations of the MCU?