Arduino based motion activated light and gas sensor for the kitchen using attiny85

I've been wanting to get my hands on arduino after seeing how powerful it is. Luckily, I was able to find a clone here in the Philippines, which is good enough to tinker with. This board is named Aceduino and is very similar to the Uno.

It wasn't hard to find what I'm going to use it for (endless possibilities!). The immediate application around the house is automation. It's not like I have a big house that flicking a switch is a big effort. There are just some things you want done automatically especially when it is going to make things safer.

For this project, I wanted it to automatically turn the kitchen counter light on and off so we don't have to touch the switch with wet hands. I shopped for a few components to go with the arduino:

• PIR sensor - to detect motion near the counter or sink
• 5V Relay - to turn the light on/off
• Some diodes, resistors and a small switch

I don't intend this to be a tutorial so unless there are people interested on the build itself, I'll skip to the good part. 

Using a few guides on the net, I was able to make a working prototype. That's when I realized this board would be a huge waste if all I'm going to use is just a couple of I/O ports.  This is where the attiny85 comes in.

Aceduino and Attiny85 

 The attiny85 has only 5 I/O ports that I can use but even then, there will be a few more unused ports if all it will do is turn on a light. I thought about other ways to make use of the extra ports and found something appropriate for the kitchen - a gas sensor.

I went to buy the additional parts:

• MQ5 Gas sensor
• Buzzer

So here are the features of the final build:

• motion activated light
• detects a gas leak and sounds an alarm when it does
• manual switch - if you want to keep the light on even when no motion is detected or if you want to suppress the alarm

It could use a better case but until I get a 3D printer, this will do.

And here it is in action:



Edit:
Here's the sketch for the attiny85 chip:

const int inPin1 = 1;   // switch connected to digital pin 1
const int ssrPin = 2;   // relay
const int pirPin = 4;   // PIR sensor
const int buzPin = 0;   // buzzer
int motionDetect= 0;
int manualSwitch = 0;
int motionSwitch = 0;
int gas = 0;
int buz = 0;

unsigned long timer;
unsigned long timerGas;
unsigned long timerPIR;
unsigned long timerBuz;
unsigned long timerBuzMin;

void setup() {
  pinMode(ssrPin, OUTPUT);
  pinMode(pirPin, INPUT);
  pinMode(inPin1, INPUT);
  digitalWrite(ssrPin, LOW);
  timerPIR = 0 - 70000;
  timerBuzMin = 0 - 6000;
  //Serial.begin (9600);
}

void loop()
{

  timer = millis();

  motionSwitch = digitalRead (inPin1); 
  if (motionSwitch == HIGH) // Motion Mode
  {
  gas = analogRead(A3); // read gas sensor
  if (gas >= 500) timerBuzMin = timer;  // range is from 0-1024
  if (timer - timerBuzMin <= 5000)
    {
      if (timer - timerBuz >= 300)
      {
        tone (buzPin, 2000, 200);
        timerBuz = timer; 
      }
    }

    //Serial.println("motionDetect");
    motionDetect = digitalRead(pirPin);
    //Serial.println(motionDetect);
    if (motionDetect == HIGH)
    {
      digitalWrite(ssrPin, HIGH);
      timerPIR = timer;
    }
    else
    {
      if (timer - timerPIR >= 60000) // turn on relay for at least a minute
      {
        digitalWrite(ssrPin, LOW);   
      }
    }
  }
  else digitalWrite(ssrPin, HIGH); // Manual on
}