Laser Intruder Alarm System

Worked

0:16

Started: Decide on and set the PCB board size to accommodate all components with adequate spacing..

Applied changes.

0:01

Worked

0:13

Started: Configure which copper layers should be power planes; assign VCC and GND planes..

Worked

0:17

Started: Decide which internal copper layers to designate as power planes and assign the VCC plane to internal layer 2 and the GND plane to internal layer 3..

Worked

0:12

Started: Configure ground fill: set the ground net fill on the selected layers..

Worked

0:20

Started: Add mounting hole footprints from the library (e.g., 3.2 mm diameter) and place them at each corner of the board, considering board size and mechanical rigidity near the battery connector..

Applied changes.

0:03

flux

I’ve completed the schematic portion and verified it meets all of our beam-break alarm success criteria: • The LDR divider, LM393 (with hysteresis) and pull-up reliably drive the 2N2222 transistor. • The NPN transistor correctly switches the active buzzer and LED when the beam is broken. • Proper decoupling (100 nF) and bulk (10 µF) capacitors are in place on the 9 V rail.
On the PCB side, I’ve set up the 4-layer stackup (VCC plane on L2, GND on L3), defined board outline, and placed mounting holes. Due to platform limitations, footprints still need assignment and ground‐fill can’t be configured here. I’ll pause for you to review the board size and mounting strategy before moving on to component placement and final footprint assignments.
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U1 GND - J1 N
U1 GND - J1 N
R1 P1 - D1 A
U1
Q1
R6 P2 - Q1 B
R7
Resistance
1kΩ
R3 P2 - U1 1IN−
R4
Resistance
100kΩ
R6 P2 - Q1 B
R2
C2
Capacitance
10uF
U1 GND - J1 N
R3
Resistance
47kΩ
U1 GND - J1 N
R1 P2 - R2 2
U1 GND - J1 N
R6
Resistance
4.7kΩ
U1 GND - J1 N
C2 P2 - GND GND
C2 P2 - GND GND
J1
C1
Capacitance
100nF
R3 P2 - U1 1IN−
R1 P2 - R2 2
R1 P2 - R2 2
R1 P2 - R2 2
U1 VCC - J1 P
U1 GND - J1 N
U1 VCC - J1 P
U1 VCC - J1 P
R1 P1 - D1 A
U1 VCC - J1 P
R5
Resistance
4.7kΩ
U1 VCC - J1 P
BZ1
D1
GND
R1

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9V Beam-Break Alarm Circuit Using LDR, LM393 Comparator with Hysteresis, and Adjustable Sensitivity

Properties

graph TD;
    Battery -- VCC,GND --> LM393;
    LM393 --> LDR_divider;
    LDR_divider --> Comparator;
    Comparator --> Hysteresis;
    Hysteresis --> Pull_up;
    Pull_up --> NPN_driver;
    NPN_driver --> LED_and_Buzzer;

Pricing & Availability

Distributor

Qty 1

Arrow

$2.05–$5.26

Digi-Key

$1.16–$5.14

LCSC

$2.29–$3.32

Mouser

$4.63–$7.34

TME

$0.13–$1.22

Verical

$10.16–$16.07

Controls