An alarm, such as a buzzer can be activated by touching a conductive surface in a touch alarm circuit that uses a IC 555 integrated circuit.
It makes use of the multimode functionality of the IC 555 device, namely the monostable mode in this instance.
Every electronics enthusiast should have at least one experience with the IC 555 when learning how to build basic and practical circuits.
Here, a buzzer is used to sound a louder alarm when the IC 555 based contact alarm circuit detects human contact.
Circuit Working:
Parts List:
| Component Type | Description | Quantity | Notes |
|---|---|---|---|
| Resistors | All 1/4 watt unless specified | ||
| 1M | 1 | ||
| 100k | 1 | ||
| Preset 100k | 2 | ||
| Capacitors | |||
| Ceramic | 0.01μF | 1 | |
| Electrolytic | 47μF 16V | 2 | |
| Semiconductors | |||
| IC | 555 | 1 | |
| Transistor | 2N2222 | 1 | |
| Miscellaneous | |||
| Buzzer | 1 | ||
| Metal touch plate | 1 |
The 555 IC is set up as a monostable circuit which means that when it receives a trigger, it produces a single output pulse for a predetermined amount of time.
External resistor and capacitor components dictate its duration.
Its touch alarm circuit is made to be portable, using a standard 9V battery as power.
Three components capacitor C3, resistor VR2 and resistor R2 control the alarms timing.
The duration of the warning may be altered by varying the value of resistor VR2.
Using the electricity from the battery, the transistor designated 2N2222 functions as a switch to turn on and off the buzzer.
Together, capacitor C1 and resistor VR1 influence how loud the alarm sounds.
The output signals form is influenced by the value of resistor VR1, which in turn affects the buzzers tone based on when the touch plate is triggered.
Formulas:
Use the following procedures and formulas to create a monostable mode circuit for a Touch Alarm using the IC 555:
Pulse Width Estimate:
When operating in monostable mode, the 555 output remains HIGH for a predetermined amount of time (pulse width) that is dictated by R and C.
The formula for the pulse width T is:
T = 1.1 × R × C
where,
- T is measured in seconds (s).
- R is the resistance measured in ohms Ω.
- The capacitance in farads F is denoted by C.
Additional Information:
To get the appropriate pulse width for your touch alarm application, adjust R and C.
Try adjusting the component values to see how the touch alarm responds best.
You may successfully create a monostable mode circuit for a touch alarm by utilizing the IC 555 and these calculations.
Based on your unique needs for response characteristics and pulse width, change the component values.
How to Build:
To build a Simple Touch Alarm Circuit using IC 555 follow the below mentioned connections steps:
- Gather all the components as mentioned in the above diagram
- Connect pin 1 of IC1 555 to ground.
- Connect pin 2 to positive supply through resistor R1, connect a metal touch plate from pin 2 of IC1 555.
- Connect pin 3 of IC1 555 to one leg of VR1.
- Connect pin 4 of IC1 555 to positive supply of +9V.
- Connect pin 5 of IC1 555 to ground through capacitor C2.
- Connect pin 6 to pin 7 of IC1 555.
- Connect VR2 preset between positive supply and pin 6/7 of IC1 555 in series with a resistor R2, and a capacitor C3 to ground.
- Connect pin 8 of IC1 555 to positive supply of +9V.
- Connect a transistor Q1 collector to positive supply through buzzer, base of transistor Q1 to one leg of VR1 preset, and emitter of Q1 transistor to ground.
Conclusion:
To conclude, this touch alarm circuit provides a transportable way to produce a sound alert that is activated by touch.
You may change the alarms tone and length by modifying a few different settings.
For anybody interested in learning basic electronics and creating their own sound based alarm, this makes it a flexible project.