Simple yet efficient alarm systems may significantly increase the safety of homes and companies at a time when security is of the utmost importance.
This simple project, the Door Knob Touch Alarm Circuit, uses a 555 integrated circuit to sense unwanted entry by touch.
When someone touches the door knob, this circuit not only serves as a deterrent but also sounds a loud buzzer to notify the homeowner or security staff.
We will examine the circuits working, design specifics, formulas, and circuit construction in this post.
Circuit Working:
Parts List:
| Component | Value/Specification | Quantity |
|---|---|---|
| Resistor (1/4 watt) | 100k | 1 |
| Resistor (1/4 watt) | 1M | 1 |
| Preset (100k) | 100k | 2 |
| Capacitor (Ceramic) | 0.01μF | 1 |
| Capacitor (Electrolytic) | 47μF / 16V | 2 |
| IC | 555 | 1 |
| Transistor | BC547 | 1 |
| Buzzer | 9V | 1 |
| Battery | 9V | 1 |
The Door Knob Touch Alarm Circuit utilizes an IC 555 monostable multivibrator to generate a square pulse upon trigger pin input.
The duty cycle and length of the output pulse may be adjusted by adjusting the variable resistor VR1.
The variable resistor VR2, which has a C3 capacitor attached to its variable pin, receives the output pulse from the timer IC555 and sends it to the transistor base, causing transistor Q1 to switch on for an extended period of time.
The timer IC 555 is set to start when a human touches the door knob; the exact timing Timing and resistor Transistor Q1 is driven by a square pulse that oscillates and is initiated by the capacitor value timer IC.
A buzzer that is attached to the Q1 collector will become biased as soon as the Q1 is turned on.
This circuit will sound an alarm for a brief period of time, which can be adjusted by varying the value of the timing component.
You may connect a relay to the timer ICs output to operate any desired electrical device.
Formulas:
The timing duration T for the 555 timer in monostable mode is given by:
T = 1.1 × R × C
where,
- R is the total resistance in ohms R1 + R2( in the circuit diagram VR1 + R2 are the total resistance).
- C is the capacitance in farads.( in the circuit diagram C1 is the capacitance).
How to Build:
To build a Your Own Door Knob Touch Alarm Circuit follow the below mentioned connections steps:
- Gather all the components as shown in the above circuit diagram.
- Connect pin 1 of IC 555 to GND.
- Connect pin 2 of IC 555 between R1 resistor and door knob.
- Connect pin 3 to center leg of VR2 and base of transistor Q1.
- Connect pin 4 and pin 8 of IC 555 to positive supply.
- Connect pin 5 of IC 555 to GND through capacitor C2.
- Connect pin 6 and pin 7 of IC 555 between resistor R2 and capacitor C1, connect VR1 preset in series with resistor R2 and capacitor C1.
- Connect transistor Q1 collector to positive supply through 9V buzzer.
- Connect transistor Q1 base to pin 3 of IC 555.
- Connect emitter of transistor Q1 to GRND.
- Connect preset VR2 center leg to IC 555 pin 3 second leg to GND through capacitor C3, and 3rd leg to base of transistor Q1
Conclusion:
The Door Knob Touch Alarm Circuit, which makes use of a 555 IC, is a simple and efficient way to increase security.
It is simple to build and reacts quickly to any illegal entry.
One may modify the circuit to suit certain requirements by being aware of the components and functioning principles.
This project gives students and hobbyists alike a worthwhile electronics learning experience in addition to its practical use.