Todays time safety is very important.
This Build Your Own Door Knob Touch Alarm Circuit can help protect home and office.
This small project is Door Knob Touch Alarm using 555 IC.
It can sense when someone touches the door knob.
If someone touches then alarm makes loud sound.
It scares intruder and warn owner or guard.
In this post we can see how circuit work with design parts, formulas and how it is build.
Circuit Working:
Parts List:
| Component | Value/Specification | Quantity |
|---|---|---|
| Resistor (All resistors are 1/4 watt) | 100k | 1 |
| 1M | 1 | |
| 100k | 2 | |
| Capacitor | Ceramic 0.01μF | 1 |
| Electrolytic 47μF 16V | 2 | |
| Semiconductors | ||
| IC 555 | 1 | |
| Transistor BC547 | 1 | |
| Buzzer 9V | 1 | |
| Battery 9V | 1 |
This Door Knob Touch Alarm uses IC 555 in monostable mode.
It give square pulse when trigger pin get input.
Output time and duty can change by turning VR1.
Output from IC 555 goes to VR2 with capacitor C3.
Then it goes to base of transistor Q1 and this make Q1 stay ON for some time.
When someone touches door knob then IC 555 start.
Time depend on capacitor and resistor.
Q1 get square pulse and turn ON.
Buzzer connect to Q1 collector.
When Q1 is ON then buzzer is also ON.
Alarm sound for short time and we can change time using timing parts.
Also we can connect relay to IC output to run other electric devices.
Formulas:
Time duration T for 555 timer in monostable mode is:
T = 1.1 × R × C
where:
- R is total resistance for R1 + R2 but in circuit it is VR1 + R2.
- C is capacitor value in farads and in circuit it is C1.
How to Build:
To build a Your Own Door Knob Touch Alarm Circuit follow the below mentioned connections steps:
- Collect all parts shown in circuit diagram.
- Connect pin 1 of IC 555 to GND.
- Connect pin 2 between R1 and door knob.
- Connect pin 3 to middle leg of VR2 and to base of Q1.
- Connect pin 4 and pin 8 to + supply.
- Connect pin 5 to GND through C2 capacitor.
- Connect pin 6 and pin 7 between R2 and C1.
- Put VR1 in series with R2 and C1.
- Connect Q1 collector to (+) supply through 9V buzzer.
- Connect Q1 emitter to GND.
- Connect middle leg of VR2 to pin 3 of IC 555.
- Connect second leg of VR2 to GND through C3.
- Connect third leg of VR2 to base of Q1.
Conclusion:
In this post for Build Your Own Door Knob Touch Alarm Circuit with 555 IC is easy and useful for safety purpose.
It works fast when someone touches the knob.
We can change circuit as needed if we know how parts work.
It is good for small project for students and hobby people to learn electronics.