Abstract

A Piezo Crystal is a component that generates electricity based on the force applied to it. It is found in most household lighters as well as microphones. Connecting the crystal from the lighter to an audio input should theoretically create a functioning microphone. The sound waves picked up by the crystal are small and don’t produce sufficient electrical signals to an audio input.  Connecting an amplifying circuit and sound conducting material to the crystal produce legible results and turn the crystal into a low quality functioning microphone.

Intro

Long neck lighters are a common household appliance that can generate a flame using a small amount of force. This is done using a clicking ignition button that the user presses. The Piezo Crystal is the component in the lighter that allows this to happen. A Piezo Crystal is a crystal that has a specific molecular structure that lacks symmetry on specific axes. When force is applied to the crystal, the structure warps and the net positive and negative charges become offset, which creates a voltage (Appendix A).

When the switch of the lighter is clicked, there is a small hammer on a spring that is released and positioned to hit the crystal. Once the crystal is hit, electricity is generated, and a spark appears at the top of the lighter. While the switch is being held, a flow of flammable gas is being fed to the top of the lighter as well. When the spark and the gas collide, the flame is produced.

Another way Piezo Crystals are utilized are in standard microphones. Fundamentally the crystal in a lighter and a microphone serve the same purpose, generating electricity based on force. The sound waves in the air function as a small force. The piezo crystal detects this force and generates electricity directly proportional to the sound waves. This electric signal is then be fed into a circuit where it is amplified and then sent to a computer or a speaker.

The hypothesis being tested is whether the Piezo Crystal from a long-necked lighter can be reutilized as a microphone.

Materials + methods

1x Long necked lighter

1x Amplifying circuit

1x Diode circuit

1x Soldering Gun

1x Cheap headphones/earphones

1x Thin piece of cardboard

1x Tape

1x Audio recording device

I started by dismantling the lighter and identifying where the spark is created at the top. Then I cut off the audio jack from a pair of headphones, leaving about two inches of wire exposed. I stripped the end of the wire and soldered the left and right audio wires together. I connected a diode circuit (Appendix B) to the wire so the voltage would not blow out the speakers. Then I soldered that circuit directly to the top of the lighter and plugged the audio jack into the camera audio input. I spoke into the lighter at varying volumes and degrees and recorded the resulting audio.

I extracted the Piezo Crystal component from the lighter and glued it to a thin piece of cardboard. I unsoldered the headphone jack and diode circuit from the lighter and resoldered it to the wires already attached to the crystal. I plugged in the audio jack and spoke into the cardboard at varying volumes. I recorded the resulting audio. I then connected a capacitor to the already existing diode circuit and recorded another audio test.

I created an amplifier circuit on a breadboard (Appendix C) and replaced the diode circuit with it. Now I had a Piezo crystal glued to a thin piece of cardboard, wired to an amplifier circuit, which itself was wired to a headphone jack. I plugged in the headphone jack to the camera audio input and spoke into the cardboard at various volumes, recorded the resulting audio.

Results

The first audio recording, with the crystal being connected to the lighter, did not have any recognizable speech being produced. My voice did not have any effect on the signal. The only signal being heard was loud noise. When I clicked the lighter button there was a brief and audible spike in the audio signal. The second audio recording, with the crystal glued to the carboard, gave the same results, with no recognizable speech being produced and only loud noise. After I connected the capacitor, the third audio recording resulted in the same loud noise, but faint recognizable speech could be heard when I talked with a loud volume.

The fourth audio recording produced recognizable audio. There was a large amount of noise, and the audio quality was low. The speech being recorded was quieter and tinnier compared to a standard microphone input.

Discussion

The fourth resulting audio recording proved the hypothesis that a Piezo crystal from a lighter can be utilized as a microphone. It also demonstrates and proves the properties of the crystal. The force applied to it is proportional to the electricity produced. If it wasn’t, then the microphone wouldn’t be able to produce a clear voice, it would just be random static.

There are various kinds of Piezo crystals for different uses, the one in a lighter is not meant to provide a clean electrical signal as one in a microphone is meant for. It is simply used to produce an electric spark. This may be a reason why there is significant noise in all of the audio recordings. A reason why the first signals weren’t being picked up by the camera audio input could be because of the inner circuits of the camera. The camera input contains circuits that will not pick up small audio signals in an effort to reduce noise. Since the electrical signal from the crystal was minuscule, it was likely being dampened by that circuit. This is the reason an amplifier had to be implemented.

Conclusion

The crystal in a long-necked lighter is functionally the same component as a crystal in a microphone. With this component and enough modification, you can successfully create a microphone from a lighter.

References:

Mould, Steve. “Piezoelectricity – Why Hitting Crystals Makes Electricity.” YouTube, YouTube, 16 May 2019, www.youtube.com/watch?v=wcJXA8IqYl8&t=0s.

“Piezoelectricity – Lesson.” TeachEngineering.Org, 17 June 2022, www.teachengineering.org/lessons/view/uoh_piezo_lesson01.

Sadaghdar , Medhi. “LIGHTER Is a MICROPHONE.” YouTube, YouTube, 6 Apr. 2020, www.youtube.com/watch?v=ZlVI7YJGHq0&ab_channel=ElectroBOOM.

Sadaghdar, Mehdi. “Microphone in a Lighter, A Piezo Application.” Electroboom, 5 Apr. 2020, www.electroboom.com/?p=1156.

APPENDIX:

(A) www.teachengineering.org/lessons/view/uoh_piezo_lesson01.

(B) www.electroboom.com/?p=1156.

(C) www.electroboom.com/?p=1156.

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