Create a Budget DIY Intruder Alarm With an ATTINY 85

The idea is to take an old speaker and generate an intruder alarm from an ATTINY85 when a signal is detected.

A button is used to simulate sensor triggers but PIRs etc can be used instead.

ATTINY85

Old speaker

Breadboard

9 volt battery

LM7805 - 9volt to 5 volt convertor

Dupont cables

Button

To program the ATTINY85, follow the instructions on https://www.instructables.com/15-Dollar-Attiny85-...

and use this code in the Arduino IDE

/* TinyTone for ATtiny85 */
//clock 1mhz internal
//usbasp programmer

// Notes
const int Note_C  = 239;
const int Note_CS = 225;
const int Note_D  = 213;
const int Note_DS = 201;
const int Note_E  = 190;
const int Note_F  = 179;
const int Note_FS = 169;
const int Note_G  = 159;
const int Note_GS = 150;
const int Note_A  = 142;
const int Note_AS = 134;
const int Note_B  = 127;

int Speaker = 1;

void setup()
{
  pinMode(Speaker, OUTPUT);
}

void loop()
{
  playTune();
  delay(10);
}

void TinyTone(unsigned char divisor, unsigned char octave, unsigned long duration)
{
  TCCR1 = 0x90 | (8-octave); // for 1MHz clock
  // TCCR1 = 0x90 | (11-octave); // for 8MHz clock
  OCR1C = divisor-1;         // set the OCR
  delay(duration);
  TCCR1 = 0x90;              // stop the counter
}

// Play a scale
void playTune(void)
{
 TinyTone(Note_C, 4, 50);
 //TinyTone(Note_D, 4, 500);
 //TinyTone(Note_E, 4, 500);
 //TinyTone(Note_F, 4, 500);
 TinyTone(Note_G, 4, 50);
 //TinyTone(Note_A, 4, 500);
 //TinyTone(Note_B, 4, 500);
 //TinyTone(Note_C, 5, 500);
}

After programming the ATTINY85, the steps are as follows:

1. Connect Pin 3 LM7805 to VCC Attiny85 and Pin 2 to Gnd Attiny85

2. Connect Pin 1 LM7805 to +ve 9V battery and Pin 2 LM7805 to -ve 9V battery

3. Add +ve terminal speaker to pin 1 Attiny85 and -ve terminal speaker to Gnd Attiny85 (via Dupont cable)

You can also add a button by changing step 3 to

3. Add +ve terminal speaker to pin 1 Attiny85 and -ve terminal speaker to button pin, then connect diagonally opposite button pin to Gnd Attiny85 (via Dupont cable)

A variety of different sensors may be used to trigger the circuit , including PIR , Ultrasonic and manual switches. The output from the speaker may be amplified using an LM386 module widely available on E-bay.

Please ensure that you adhere to strict electrical safety guidelines, i.e.

1. Seek guidance from a person competent in electrical safety such as a qualified electrician.

2. Use low voltage.

3. Ensure that all connections are secure, cables are intact and do not lead to electrical shorts.

4. Etc