Learning Electronics

Learning Electronics

Learn to build electronic circuits

Electronic Candle Blow Out Schematic

LED or bulb switch off with a puff, Funny gadget - 3V Battery supply

This design was developed by request of a correspondent having made a sort of LED candle and needing to switch off the LED with a puff. This simple, easy to build gadget can be useful as a prop for Halloween and Christmas season, shows and the like. Q2 & Q3 form a self-latching pair that start operating when P1 is pushed: in this way the LED (or bulb) will illuminate steadily. When someone emits a strong puff in the vicinity of the small electret microphone,

The resulting signal will be greatly amplified by Q1 and a rather long positive pulse (shaped by D1 and C2) will reset the self latching pair through the Emitter of Q2. The very low (and unusual) value of C1 acts as a simple high-pass filter, in order to prevent that normal speech or environmental noise shut off the device. Obviously, such a simple filter cannot be very discriminating, therefore, not only a strong puff will reset the circuit but also a loud shout, blow, clap or stroke.

Circuit diagram:
 electronic candle blow out schematic circuit diagram
Electronic Candle Blow Out Circuit Diagram


R1 = 10K
R2 = 1M
R3 = 1K
R4 = 4.7K
R5 = 10K
R6 = 100R
C1 = 100pF-63V
C2 = 10µF-25V
C3 = 100nF-63V
D1 = 1N4148
D2 = Red LED
P1 = SPST Pushbutton Switch
B1 = 3V Battery (2 x 1.5V AA, AAA Cells in series etc.)
Q1 = BC550C-45V 100mA NPN Transistor
Q2 = BC337-45V 800mA NPN Transistor
Q3 = BC327-45V 800mA PNP Transistor
MIC1 = Miniature electret microphone

Source: Red Free Circuit Design