Lie detector electronic project circuit design using transistors

This lie detector electronic project is designed using few common electronic parts. This lie detector can test a person whose status is modified in certain situations (as in the polygraph test) by "observing" biofeedback. Because a person's skin resistance depends on the state in which that person is, skin resistance increases with depth state of relaxation.
The electronic scheme presented, affects skin resistance frequency of oscillator built with transistor T2 . Both electrodes, with ring shape, are applied on two fingers of a hand. The more deep state of relaxation corresponds to a lower frequency sound that you will hear in your headset.
The second oscillator, built with transistor T1 also produce sound. In this case you can still adjust the height of the potentiometer P1 sound at frequencies corresponding to the other oscillator, the deepest state of relaxation. If the two oscillator signals are run separately to a stereo headset, the maximum relaxation is achieved when sound from the right side sounds has the same frequency like sound from the left side.

Circuit Diagram:

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Power amplifier using transistors

 

Using some power transistors and some other common electronic components, can be designed a high power audio amplifier capable to provide a maximum output power of 90W.
This power amplifier based on transistors is capable of provide an output of 70W on a load of 8 ohms or 90W on a 4 ohms load.
If the component values in parentheses are used can be connected speakers with 4 ohm impedance, in which case the amplifier maximum output power will be around 90 watts.
The input signal is brought to the transistor T1 and the reaction is taken on the basis of T2. Current through deferential stage is kept constant at 1 mA current source through the action of T3. The input signal for T4/T8 transistor is taken from the T1's collector in combination with current source T5 forms a control stage class A for power transistors. Current through control stage is quite small (about 7 mA) as T6 and T9 are Darlington power transistors.
Protection circuit from Fig. 2 must also be changed when using a 4 ohm load. R24 and R28 values are then 3k9, R26 and R28 are 220 ohms, and D5, D6 and R30 are all eliminated.
Rectified voltage for 70 W / 8 ohms version is ± 40 V to be in load, no load, this corresponds to about ± 47 V. At 4 ohms, these values are ± 34, respectively, ± 40 V.
The transformer used must provide for alternative 1A 70 W / 8 ohm (mono) and 2.2 A for version 90 W / 4 ohms.

Circuit Diagram:

Electret microphone amplifier circuit using transistors

This electret microphone amplifier is designed using common electronic components . This microphone amplifier uses an electret microphone capsule, but can be an dynamic microphone, which have a low resistance. This circuit requires a supply voltage between 5 and 10 volts, is recommended to use a supply voltage of 9 volts DC . Since the circuit has a very low power consumption (about 1.5m), circuit can be powered using a 9 volt battery. The values for R1, C3 and R8 are for Philips LBC1055/00 electret capsule.
Amplification depends on the ratio R7/R3, is greater than 100.

Circuit Diagram:

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