A flame is a conductive medium that can be used in an uncommon feedback loop to control the frequency of an audio oscillator. This configuration can be used as a confirmation of the conductivity of a flame.
The audio oscillator described in this project is controlled by the 'Tourth" matter state, the "Plasma" or an ionized Gas, and Can be used as part of an interesting experiment in physics.
The flame can be produced by a simple match or a candle and the flickering effect will modulate the generated sound.
The circuit runs in frequencies between 1 and 500 Hz, depending on the electrodes and flame positions.
A schematic diagram of the Plasma Oscillator is shown in circuit .The high input impedance of a 40938 is fundamental in this project. A flame typically has a resistance in the range of tenths of megohms.
The printed circuit board for the components positioning is shown in circuit. Sensor details are also given in that figure. Two wires, one placed near the other, with about 1 inch of bared length as shown in the figure, form the "plasma sensor. The flame should involve the two bared wires at the same time to allow the feedback current to flow and the oscillator to operate.
An output stage using a piezoelectric transducer can replace the transistor and loudspeaker. With a lower current drain this configuration can be powered from four AA cells or a 9V battery.
Parts List - Plasma Oscillator
IC1 - 40938 CMOS Integrated Circuit
SPKR - 4/8 ohm 4-inch loudspeaker
Q1 - 8D135 orTlPSl Power NPN silicon transistor
R1 - 10,000 ohm, 1l4W,5olo resistor
R2 - 1,000 ohm, 114W,5% resistor
X1 - Plasma sensor - see te)ft
C1 - 1,000 to 4,700 pF ceramic or metal film capacitor
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