Fun With a Lie Detector!

Step 3: Build the circuit...

Following the schematic shown here, build the circuit. Take your time and make good solder joints.

Comments

[ETfonehome]

How do you tell if someone is lying to you? Does the speaker change tone or something like that?

[punom]

where the R2 resistor ends?

[tceferino]

Pienso, que el final de R2 es tu dedo, cuando aterrizas con R1.

[dog digger]

It goes to a finger pad. The line sticking out in between C1 and R1 goes to the other finger pad

[MrMistermister]

Is there a switch? Or does it turn on when you put on the finger pads?

[mshahzeb]

i have same problem no sound is coming from speaker.

[dwatord26]

could you post a picture of it on the circuit board. I have yet to learn how to read these

[TheIronHobo]

well try first. this was actually the first circuit i ever built(it worked) its pretty easy when you read the key like in a map and it just takes some think work

[chisse]

Hi im bilding your Lie Detector but I cant get it to work. I added the Transistors the Resistors and the capacitor and my speker. But not sure where the batteries go. Also can the Resistors be 1W? If some one can help me out that would be cool Thanks.

[brooklynlord]

The wattage of the resistors just means the maxium power the resistor can handle before it overheats and (literally) blows up. So yes, they should be able to be replaced with 1W resistors without any problems, even though it is a quite big overkill.

The batteries are at the top of the schematic and they are hooked up to the PNP transistor's emitter and the emitter of the NPN transistor and the speaker.

[oweng4000]

Will 47k resistor work instead of the 82k?

[oweng4000]

Thx kipkay.  I will be using this as a music maker.

[microboard]

Can you solder on  an LED where the speaker would go so when someone tells a lie the LED flashes?

[M4industries]

Are the Emitter and base pins connected on Q1?

[godfreyandthandi]

no they are not.