STEM WAREHOUSE KI0208 Light Alarm Kit User Guide
- June 6, 2024
- STEM WAREHOUSE
Table of Contents
Light Alarm Kit
COMPONENTS
Component List
| Designator | Part Description | Part No. |
|---|---|---|
| R1 | 100K 0.25W 5 % Resistor (Brown, Black, Yellow) | RS1725 |
| R2 | 4M7 0.25W 5 % Resistor (Yellow, Purple, Green) | RS1925 |
| R3 | 240K 0.25W 5 % Resistor (Red, Purple, Yellow) | RS1775 |
| R4 | 4K7 0.25W 5 % Resistor (Yellow, Purple, Red) | RS1565 |
| C1 | luF, 50V RB Capacitor | CC1401 |
| C2 | 1 nF, Ceramic Capacitor | CC0011 |
| C3 | 47uF, 16V RB Capacitor | CC1438 |
| VR1 | 500K Horizontal Trimpot | PT8175 |
| IC | 4093 CMOS IC | X-4093 |
| SW1 | DPDT Push ON-OFF Switch | SW1845 |
| SP1 | Miniature PCB Speaker | SP1200 |
| PT1 | IR Photo Diode | L51P3C |
| Q1 | PNP TO-92 Transistor | BC557 |
| Q2 | NPN TO-92 Transistor | BC547 |
| Bat1 | 9V Battery Snap | BA9000 |
| Skt | 14 Pin IC Socket | IC1014 |
CIRCUIT DESCRIPTION
Circuit Description
The light alarm circuit uses an L51P3C photo-diode. It is an opto sensor, its’
electrical characteristics change in the presence of light.
The light sensed may or may not be in the visible spectrum. In dark conditions
their resistance is high; typically millions of ohms.
In light conditions, the resistance falls to something like 30 ohms in bright
sunlight.
Many practical uses of this property are possible.
PCB Component Overlay
CONSTRUCTION
THE DETECTOR
In dark conditions the L51P3C is virtually an open circuit. No Current flows
through the 500k potentiometer into the base of the transistor. Thus the diode
is OFF and the logic level on the input line to the 4093 is LOW.
THE 4093 TANK CIRCUIT
The 4093 CMOS IC is a quad 2 input NAND SCHMITT TRIGGER IC (there are four of
the gates in them), and the four gates shown on the diagram are all in the one
IC. It is wired up to oscillate when the input to it goes high, that is the
BC557 transistor turns on after light is detected by the L51P3C. The
oscillating output from the 4093 turns the BC547 on and off. This creates a
square wave signal which drives the speaker.
Fig.2 Assembled Light Alarm
In digital logic, a HIGH is also referred to as a “1” and a LOW as a “0”.
After the alarm has been operating and it is put back into dark conditions
again, the alarm will continue to sound for about 3 seconds. This is due to
the 1uF capacitor Cl keeping the input to the 4093 HIGH. To increase the
delay, increase the value of this component.
COMPONENTS
Westfield anetuagas
RESISTOR COLOUR CODE GUIDE
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