Simple Lie Detector (from Solid Components)





Introduction: Simple Lie Detector (from Solid Components)

About: Hi, I'm Tamas (Thomas), a 19 years old Hungarian guy. My hobby started more than 10 years ago. I learn electronics, physics, programming, IoT and I'm sharing my projects with you, hope you like it!

During the summer I have many times to build gadgets, and when I found this easy circuit on the internet I' ve decided to make my own and to show you how to build a lie detector. First of all I am 15 now and now learn english in the school so sorry for my bad english. When you put your fingers on the touchpads you activate the circuit and you will hear a static noise. If you lie your fingers will get moist and the speaker will change its noise.

Step 1: Tools and Materials

*Materials: 2 AA Batteries

-Battery box

-9V battery clip (if you have a battery box like me)

-A small cardboard box

-A 8R speaker

-2x100k and 1x1k resister

-1 BC557 transistor and 1 BC547 transistor

-Electrical Tape

-2 pieces of 1.5x1.5 inch aluminium foil


*Tools: Soldering Iron, Glue Gun, Needle

Step 2: Making the Circuit

I've made my circuit with an other speaker, but it worked fine. You need to solder two wires to the touchpads, because those will come out from the box. Be careful with the transistors, one of them is NPN and the another is PNP.

Step 3: Building the Case

1. With a glue gun we need to glue everything inside the cardboard box. On the bottom I put the 9V battery clip, because my battery box can connect to it, on the top is the speaker. With a needle you need to make two holes for the wires of the touchpads and ten or more holes for the speaker. The electronics are just simply soldered together, not on a PCB board. You can make another design. At the end you need to make the touchpads, which connects to the two wires.

Step 4: Testing

Put your fingers on the touchpads, and lie for a question. If you lie you will hear a static noise.

Now make your own lie detector and try it on a freind!
This is an easy project for school, or just for fun. I hpe you like it!



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41 Discussions

what is the red circle thing that Is in between some of the wires.

What is the red circle thingy in the wires?

We are doing this for a GT project and we can’t figure out how to make this circuit . Will you please help us?

is there anyway you could email me in detail how to make my own lie detector like the one you made here i am not that experienced with building electrical things also what did you use for the finger touch pads? I have all the tools and materials you listed I just not sure how to put them all together to make it work right! Thank you in advance for your prompt attention and help with this matter it is so that i can help my daughter with building it! You can email me at asap pppplllllleeeaaaaassssseeeeee

Your English is outstanding - your Instructable is clearer and better written than MANY by native English speakers. Keep up the good work. Nice project!

2 replies

Hi this is a grate site good job love it. = )

how long does it last?

p.s how many stuff have you built?

how do you put the wires andall the transitors and resisters together

what is the scientific explanation of this project???. i want to know how every component worked.
thank you

would a 9v battery fry the circut

Also could you clarify what the battery box is?

1 reply

It's a bettery box for 2 AA batteries.

Could you provide a rough estimate of the time taken to build this? Trying to do some time planning.

1 reply

Hm, if you have the parts already one or a half hour is enough. So isn't a hard project.