This simple design for a motion detector uses an IC 555 to detect human trespassing from a distance.
Usually, there are two major components to this circuit:
The IC 555 is used in this part as an astable multivibrator, in other words it produces a constant frequency specific square wave.
This high frequency beam is emitted by an infrared IR sensor.
This part detects the transmitters infrared beam using a phototransistor.
The phototransistor conducts and starts the IC 555 in the receiver portion when movement breaks the beam.
This activates an output that indicates motion detection, such an LED or an alert.
This circuit requires the components such as 555 ICs, resistors, capacitors, an IR sensor, a phototransistor and an output device like an LED or a relay.
Circuit Working:
Parts List:
| Component Type | Description | Quantity |
|---|---|---|
| Resistors | 68Ω, 1/4 watt | 1 |
| 1.5k, 1/4 watt | 1 | |
| 1M, 1/4 watt | 1 | |
| 1k, 1/4 watt | 1 | |
| 10k, 1/4 watt | 4 | |
| Preset 1M | 1 | |
| Capacitors | Ceramic 0.47μF | 1 |
| Electrolytic 10μF, 50V | 2 | |
| Semiconductors | IC 555 | 2 |
| Transistors BC547 | 3 | |
| Diode D1 1N4007 | 1 | |
| LED (any 5mm, 20mA) | 1 | |
| IR Transmitter Photodiode | 1 | |
| IR Receiver Phototransistor | 1 | |
| 12V Relay | 1 |
Infrared proximity detectors are essential and widely used components in automation systems.
We commonly encounter them in automatic water dispensers, hand dryers and even some automatic doors.
This circuit utilizes the 555 IC to generate short bursts of high voltage pulses at a specific frequency.
These pulses are emitted as infrared IR beams by an LED.
The IR beams are focused on the area of interest.
If something enters this area, the IR beams are reflected back and detected by a phototransistor.
When the phototransistor receives the reflected signals, it triggers a relay and an alarm.
The relay stays activated for a specific time determined by the circuit components.
To test the circuit, you can move your hand within a meter of the IR beam and observe the relays response.
In reaction to this, the relay activates and remains ON based on the monostable predefined time delay established by the 10uF capacitor and the 1M resistor.
This confirms the circuits functionality.
The 1M preset allows you to adjust the circuits sensitivity.
This means you can control how close something needs to be to trigger the alarm.
Formula:
The formula used to calculate the astable multivibrator frequency (f) in the transmitter component of the IC 555 based motion detector circuit is crucial:
f = 1.44 / (R3 + 2*R4) * C
R3, R4 and C1 are associated with the IC1 555 which is configured as astable multivibrator
The sensitivity of the motion detection may be changed by changing the frequency of the infrared pulses that the circuit produces, which can be done with this formula.
How to Build:
To build a Motion Detector Circuit using IC 555 follow below mentioned steps:
- Gather all the components as mentioned in the above diagram.
- Connect pin 1 of IC1 555 to ground.
- Connect pin 2 to pin 6 of IC1 555, connect a capacitor C1 from pin 2/6 of IC1 555 to ground.
- Connect pin 3 of IC1 555 to IR transmitter photodiode to ground through resistor R1.
- Connect pin 4 and pin 8 of IC1 555 to positive supply of +12V.
- Connect from positive supply in series a IR receiver phototransistor to one leg of preset VR1.
- Connect resistor R4 between pin 6 and pin 7 of IC1 555.
- Connect resistor R3 to positive supply from pin 7 of IC1 555.
- Connect pin 1 of IC2 555 to ground.
- Connect pin 2 to pin 6 of IC2 555, connect resistor R7 to positive supply through pin 2 of IC2 555
- Connect pin 3 of IC2 555 to base of transistor Q3.
- Connect pin 4 and pin 8 of IC2 555 to positive supply of +12V.
- Connect pin 6 and pin 7 of IC2 555, connect a capacitor C3 from pin 6/7 of IC2 555 to ground.
- Connect resistor R8 to positive supply from pin 7 of IC2 555.
- Connect a LED and resistor R5 in series from positive supply to collector of transistor Q1.
- Connect transistor Q1 collector to collector of transistor Q2, connect base of transistor Q1 to first leg of preset VR1 through resistor R2, connect emitter of transistor Q1 to ground.
- Connect collector of transistor Q2 to collector of transistor Q1, base of transistor Q2 to emitter of transistor Q1, and connect emitter of transistor Q2 to ground.
- Connect collector of transistor Q3 to positive supply through diode D1, connect base of transistor Q3 to pin 3 of IC2 555, and emitter of transistor Q3 to ground.
- Connect a 12V relay coil leg one between positive supply and diode D1 and second coil leg between diode D1 and collector of transistor Q3.
Conclusion:
The 555 IC based motion detector circuit provides an easy and efficient method of detecting movement.
It works by producing and sending infrared pulses, detecting their reflections using a phototransistor, and setting off an alarm or relay when they are detected.
Applications for this circuit may be found in many automation systems, such as security systems and water dispensers.