Arduino-Based Shadow alarms are usually used for protection against theft. A shadow alarm is a device that sounds an alarm when a shadow falls on it. Described here is a simple circuit of an Arduino based shadow alarm. This compact shadow alarm unit is capable of sensing a moving shadow in a restricted area, and can be easily installed on wall, window or door to protect your valuables from theft. Constant lighting is required in the confined area to detect the moving shadow.
Step 1: Get the parts
T1, T2 – BC547
D1,D2 – 1N4007
LED – 5mm light emitting diode
R1,R4 – 1k resistor
R2,R3 – 470 ohm resistor
VR1 – 4.7k preset
LDR – Light dependent resistor
C1 – 470uf, 25v electrolytic capacitor
C2 – 100uf, 16v electrolytic capacitor
Batt.1 – 9v battery
CON1 – 7 pin male header
CON2 – 1 pin male header
Note: I have used Freeduino instead of Arduino Uno but I have also tested with Arduino Uno .
Step 2: Make the alarm system
1) Take a dotted PCB having 16 x 11 holes
2) Write numbers and alphabets on the PCB as shown in the above figure
3) Place the components on the PCB as shown in the above figure
4) Solder the components
5) Solder the wires
Step 3: Prepare the shadow sensor
1) Cut a female to female header pin wire into two
2) Take a LDR and solder the wires as shown in the above figure
Step 4: Programming
1) Download shadow_alarm.ino from here
2) Connect Arduino to your PC
3) Click on upload
Step 5: Connections
1) Connect the 1st pin of the shadow alarm circuit to Vin of the Arduino.
2) Connect the 2nd pin of the shadow alarm circuit to pin 10 of the Arduino.
3) Connect the 3rd pin of the shadow alarm circuit to the LDR and other pin of LDR to Gnd.
4) Connect the 4th pin of the shadow alarm circuit to 5v of the Arduino.
Read more: Arduino-Based Shadow Alarm