A dark detecting circuit for your jack-o’-lantern

Fall is in the air and todays idea comes from Mad Evil Scientist.   Instead of purchasing small battery operated tea lights lets buy some LED's and make our own pumpkin that automatically shuts off when it's daylight.

Click here for full directions and diagrams.


  • A phototransistor (we use type LTR-3208E)
  • 2N3904 (or similar) transistor, QTY 2.
  • 5k ohm resistor
  • Yellow or red LEDs, QTY 2. (We used 10 mm diffused yellow LEDs)
  • 50 ohm resistors (one for each LED)
  • Battery holder with 2 AA-size alkaline batteries