LDR Based Aircraft Warning Signal Light Circuit

In tall buildings, towers or high structures it is important to show warning light for aircraft safety.

Normally a red 230V LED bulb is used as warning lamp.

This LDR Based Aircraft Warning Signal Light Circuit automatically switches ON the bulb in night and switch OFF in day.

It uses LDR sensor, relay and small power supply.

This saves electricity and reduce manual operation.

Circuit Working:

Parts List:

In the above circuit 230V AC is step down to 12V AC by transformer T1.

Bridge rectifier change AC to DC and capacitor C2 filter DC and gives supply to control part.

LDR is main sensor in the circuit

When mains is ON the bulb glows.

Light fall on LDR and its resistance goes low with more voltage goes to base of transistor Q1 and so Q1 turns ON.

Relay activates and bulb switches OFF.

Now no light is on LDR as its resistance goes high and base voltage drops with Q1 turns OFF.

Relay deactivate and bulb glow again.

This cycle repeats and bulb keep flashing.

Capacitor C1 across relay keep relay ON little longer so bulb stays OFF for some extra time.

Fix LDR near bulb so light falls on it.

After wiring power ON the circuit and adjust pot VR1 until bulb start flashing.

Reminder: Be careful some parts have high voltage and can give shock.

Formulas:

Formulas for Vout across LDR and R1 and VR1 divider is given by:

Vout = Vin * (Rfixed / (Rfixed + RLDR))

where,

• RLDR is the resistance of LDR which depend on light.

In day RLDR is few hundred ohm and at night RLDR is 100k or more.

Transistor base require around 0.7V to turn ON.

So we need to adjust pot value so that base get this voltage only when dark.

Relay used is 12V SPDT with 1A rating.

Bulb connected at 230V side of relay.

How to Build:

To build a LDR Based Aircraft Warning Signal Light Circuit follow the below steps for connection:

• Gather all the circuit parts as shown in diagram above.
• Transformer T1 connects to 230V mains and secondary 12V AC goes to bridge rectifier.
• Bridge rectifier output connects to filter capacitor C2 positive.
• LDR one end goes to positive supply and other end to junction of R1 and VR1.
• R1 47k resistor connects from base of Q1 transistor.
• Potentiometer VR1 200k one pin is also connected in divider network with LDR and other pin to GND
• Q1 collector connect to one end of relay coil and other end of coil goes to +12V.
• Connect capacitor and diode D1 in series as shown in circuit diagram
• Relay common pin connects to 230V supply with N/C pin to bulb and other end of bulb to T1 transformer of 230V AC

Conclusion:

This LDR Based Aircraft Warning Signal Light Circuit is simple with low cost solution for aircraft warning lamp.

It works automatic in day and night with no need for manual switching.

Sensitivity can be adjusted using potentiometer.

Circuit can handle 230V bulb safely using relay isolation.

It is very useful for towers, buildings, chimneys and other high structures.

References:

NE555 + CD4017 Airplane Strobe Light with LDR