Puff to OFF LED Circuit

 This article explains you how to make a puff to off led electronic circuit. Candles are not new to us. They are being used since ages for the birthday parties, decoration or a certain premise. Electronics is used everywhere. Candles are no exceptions and electronics has also helped to devise candles which look. Here we have presented a simple circuit that turns off the LED just by a puff.

Puff to Off LED Circuit Working Principle:

The main principle of the circuit is to turn off the LED by a puff. The puff applied to the mic is converted into a voltage whose value is very small. This voltage is amplified and applied to the circuit in order to make the led turn off.

Also Read the Post: How LED Flasher Circuit Works?

Puff to Off LED Circuit Diagram:

Puff to Off LEDs Circuit Diagram

Circuit Components:

• Electret condenser mic
• Light Emitting Diode
• BC 550 (NPN )transistor
• BC 337 (NPN )transistor
• BC 327 (PNP )transistor

Puff to Off LED Circuit Description:

 The proposed circuit mainly consists of mic, LED, transistors, resistors, capacitors.

 An electret condenser MIC is used to sense the puff. This condenser mike is used to convert the acoustic signal into electric signal. They have high sensitivity to loud sounds. This acts like a transducer by converting the analog signal to the electrical signal. The electret microphone is a electrostatic induction based microphone. Positive terminal of the mike is connected to the capacitor C1 and the negative terminal is connected to the ground. The MIC is connected to the transistor through a capacitor C1.This capacitor C1 acts as a high pass filter and prevents the device from shut-off.

A red LED is used in the circuit has cut off voltage of 1.7v.The light emitting diode emits the energy in the form of light while the normal LEDs emit energy in the form of heat. Light emitting diodes can resist up to a value of 3v.If the applied voltage is greater than this voltage LEDs may get damaged. The led positive terminal is connected to the latching pair and push button. Negative terminal is connected to the ground through a resistor of 100 ohm resistance

Both PNP and NPN transistors are used in the circuit. BC550 is an NPN transistor. Initially it is open circuit and it starts conducting from emitter to collector only when the base has its cutoff voltage. These transistors are used for amplifying the incoming signal from the MIC. This amplified voltage is applied to the latching pair. BC 327 is a PNP transistor. When there is no voltage applied to the base emitter and collector is in conducting state. When the base is supplied with cut-off voltage emitter and collector stops conducting. The collector of the BC 327 is connected to the base of the BC 337 transistor which is a PNP transistor. These two acts as latching pair. These two are mainly responsible for turning off the LED. A 4.7kohm resistor is connected to the ground from the emitter of BC337 transistor and 10kohm from the base to the ground.

The output from transistor Q1 is coupled with the latching pair through a signal diode in parallel to a capacitor C2 of 10uf. Diode along with C2 shapes the positive pulse that will reset the latching pair. A resistor of 1Mohm is connected from capacitor C1 to the signal diode.

Puff to Off LED Circuit Working:

• Initially, give the connections as shown in the circuit diagram.
• Connect a battery of 5v as shown.
• Now press the push button S1.
• The transistors Q2 and Q3 wired as latching pair gets activated.
• Thus drives the LED to glow.
• When you puff at the MIC, the analog sound signal is converted into a voltage signal at its output.
• This voltage is amplified by the transistor Q1.
• The amplified signal is applied to the latching pair.
• Thus base of the transistor gets the required voltage and PNP transistor stops conducting.
• Thus LED stops glowing.
• Now press the push button again in order to switch it again. 

  Puff to Off LED Circuit Applications:

  • This can be used as a candle.
  • The circuit can be used as decorative item in church and during special occasions. Get an idea about the working of LED Christmas Lights Circuit.
  • Stained glass lamps & lanterns uses this circuit.
  • This can be used in arts and crafts applications.
  •  Model railroading accessories utilizes this circuit.
  • This can be used in haunted houses and spooky lighting.
  • This can be used in automotive novelties.