Here’s a simple project for your Halloween celebration. The other day while looking through our box of Halloween decorations, we noticed that the incandescent lamp in one of the jack-o’-lanterns was burnt out. Instead of simply replacing the outdated bulb, we decided to build a small dark detecting circuit with 2 yellow LEDs based on this Evil Mad Scientist Laboratories design. After successfully building the circuit, we took the project one step further by incorporating an Atmel ATtiny13 microcontroller. The code switches the LEDs on and off randomly for a flickering effect and is based on this instructable. Below is the schematic we created in EAGLE and a parts list.

• T1, T2: 2N3904 transistors
• T3: LTR-3208E phototransistor
• LED1, LED2: 10mm diffused yellow LEDs
• R1: 5kohm resistor
• R2, R3: 50ohm resistors
• IC1: Atmel ATtiny13
• Source: 2xAA battery case with batteries