Automatic Dark Detector Cum Jack-o'-lantern




I am making a jack-o'-lantern using a simple Automatic Dark detector..

For the Automatic Dark detector..

Things you require -

# 1 BC547 transistor

# 1 LDR

# 1 LED (any color of your choice)

I have used white LED for demo and Red LED for lantern

# a 100K resistor

# a 100R resistor

# a 9V Battery

and of course a breadboard

Step 1:

Insert BC547 transistor into breadboard

Step 2:

Connect emitter of transistor to negative supply of battery.

Step 3:

Connect one end of LDR to base of transistor and other to negative supply of battery.

Step 4:

Connect 100k resistor to the base of transistor and to positive end of supply.

Step 5: Almost Done...

Connect 100R resistor to positive end of supply and insert other end anywhere in breadboard. To this end connect the positive end of LED. Connect the negative terminal of LED to the collector lead of transistor.

Step 6: Supply the Circuit..

Connect the battery to the respective terminals on breadboard and observe the LED.

When light level on LDR decreases i.e. when surrounding is dark - the LED glows otherwise LED remains OFF.

Step 7: Automatic Dark Sensor Action

Step 8: Halloween Is Round the Corner...

After your Automatic Dark detector is ready you can use it for a cool and classic Jack-o'-lantern.For the lantern use simple cardboard cut outs. Cut out the pattern or any other design of your choice. Place your automatic detector inside the lantern and then wait for the night... Lantern will lit up when it's dark...pretty cool..huh??

Happy Halloween !!

Step 9: The Circuit on PCB..

I made the same circuit on PCB by soldering the elements I had used on breadboard and it works perfectly well.

2 People Made This Project!


  • Frozen Treats Challenge

    Frozen Treats Challenge
  • 1 Hour Challenge

    1 Hour Challenge
  • Colors of the Rainbow Contest

    Colors of the Rainbow Contest

6 Discussions


2 years ago

Hi! May I know what are the steps on making this project on PCB? :)

1 reply

Reply 1 year ago

I shall write another instructable for that soon. Stay tuned :)


2 years ago

I would change the 100 ohm resistor to about a 330 ohm one because when the transistor is in full conduction, 90ma of current is flowing through it. Usually LEDs are set to run with about 20ma to 30 ma. It would make the LED last longer. JMHO

1 reply

2 years ago

Something like this would be really useful for our jack o'lanterns :)

1 reply