Halloween Flashing-eyes Badge

Two-LED-eyes follow the rhythm of music or speech

3V Battery-operated device suitable for pins or badges

Circuit diagram:

Black Cat
Halloween Flashing-eyes Badge
Halloween Pumpkin


R1______________10K  1/4W Resistor
R2_______________1M  1/4W Resistor
R3_______________1K  1/4W Resistor (See Notes)

C1_______________4µ7  25V Electrolytic Capacitor
C2______________47µF  25V Electrolytic Capacitor

D1,D2_________LEDs (2mm. preferred - See Notes)

Q1_____________BC547  45V 100mA NPN Transistor
Q2_____________BC557  45V 100mA PNP Transistor

MIC1___________Miniature electret microphone

SW1_____________SPST  Miniature Switch

B1________________3V  Battery (2 x 1.5V AA, AAA Cells in series etc. - See Notes)

Device purpose and Circuit operation:

This circuit was purposely designed as a funny Halloween gadget. It should be placed to the rear of a badge or pin bearing a typical Halloween character image, e.g. a pumpkin, skull, black cat, witch, ghost etc.
Two LEDs are fixed in place of the eyes of the character and will shine more or less brightly following the rhythm of the music or speech picked-up from surroundings by a small microphone. Two transistors provide the necessary amplification and drive the LEDs.