How does this circuit work?

[audioguru]

The simple circuit is for grade 2 in Canada or grade 7 in the USA.

With the few volts from this circuit across a victim's fingers then the input current is very low.
The meter needs 1mA for full scale but the transistor amplifies the input about 200 times so the input current is only 0.005mA for full scale in the 1mA meter.

The transistor conducts when it has DC base current. The capacitor filters out AC interference and does not affect the DC base current.

The guy who calls everybody "dear" is wrong.

 

[thetmagic]

This can't be grade 2, maybe to build it, but not how it works. 2nd graders can'tknow what electrons, transistors and etc are. I meant how it works. What grade level do you think understanding it is? Also, can you help me with my questions?

Thank You!

 

[audioguru]

I learned about electronics when I was 12 but could have learned it much earlier.
This circuit is extremely simple and should not be a school project.

 

[thetmagic]

I am in grade 8, and I am one of the best students, and I am having a little bit of trouble with this, I doubt that 2nd graders would understand how to make a lie detector and, about transistors, PN Junctions, etc. When I was in grade six in a school that is harder than normal, I started learning about electronics, like how to connect two wires to a battery and then to a light bulb, and I felt like a scientist, lol. But I really don't think that second grader would know this, they barely know how to read. Anyways, please help me with my questions.

Thank You!!!!

 

[thetmagic]

If it is so simple, how can I make another device that measures skin perspiration, that is more complex (and more useful)? I have to measure it quantitatively.

Thank You!

 

[thetmagic]

Also, I now understand how it works, but I just don't understand why there are resistors, and why you need a transistor and a capacitor, because the circuit would work without them.

Thank You!

 

[BrownOut]

I am in grade 8, and I am one of the best students, and I am having a little bit of trouble with this, I doubt that 2nd graders would understand how to make a lie detector and, about transistors, PN Junctions, etc. When I was in grade six in a school that is harder than normal, I started learning about electronics, like how to connect two wires to a battery and then to a light bulb, and I felt like a scientist, lol. But I really don't think that second grader would know this, they barely know how to read. Anyways, please help me with my questions.

Thank You!!!!

Pay no attention to the critics. There are some on here who don't get enough attention at home, so they come in here and act up. You're doing fine and it would make a great school project. We did this sort of thing when I was your age too.

 

[audioguru]

When I was in grade 1 I took the speaker from one radio and connected it to the phono input of another to make a spy amplifier. My parents were amazed.

This simple lie detector circuit has only 6 electronic parts plus two batteries. Any little kid could easily learn how it works.

 

[BrownOut]

Also, I now understand how it works, but I just don't understand why there are resistors, and why you need a transistor and a capacitor, because the circuit would work without them.

Thank You!

The transistor and associated components make you intrument more sensitive. You might try to make something work without them, but the performance will be much worse.

 

[thetmagic]

When I was in grade 1 I took the speaker from one radio and connected it to the phono input of another to make a spy amplifier. My parents were amazed.

This simple lie detector circuit has only 6 electronic parts plus two batteries. Any little kid could easily learn how it works.

I would be amazed if it was my child. And I don't think any little kid could learn this, it depends on what you consider a little, and I don't think many little kids understand a lot about biasing, semiconductors, PN Junctions, electrons, and etc. Again, it depends on what you consider a little kid.

Thank You!!!!

 

[thetmagic]

Sorry if I offended you, I didn't mean to, I just meant that this is not a smartness contest, it is a question.

 

[thetmagic]

The transistor and associated components make you intrument more sensitive. You might try to make something work without them, but the performance will be much worse.

Thank you, that was helpful!

 

[thetmagic]

Pay no attention to the critics. There are some on here who don't get enough attention at home, so they come in here and act up. You're doing fine and it would make a great school project. We did this sort of thing when I was your age too.

Thank You!!!!

 

[thetmagic]

Since this is simple, can anyone show me a more complex one (and is more useful)? Even though I do agree with BrownOut, I like challenges. Thanks BrownOut! audioguru you were so nice and helpful in the beginning, what happened?

Thank You!!!!

 

[thetmagic]

The guy who calls everybody "dear" is wrong.

LOL. But if he was wrong, what is right, please explain me.

Thank You!!!!

 

[audioguru]

Maybe you did not see what I wrote yesterday:
"With the few volts from this circuit across a victim's fingers then the input current is very low.
The meter needs 1mA for full scale but the transistor amplifies the input about 200 times so the input current is only 0.005mA for full scale in the 1mA meter."

 

[thetmagic]

Sorry for what I wrote before, I will edit it tommorrow, I was mad. I just wanted to appologize again.

 

[thetmagic]

So after the transistor amplifies it, it has enough mAs? And what are the resistors for?

Thank You!!!!

 

[BrownOut]

A transistor doesn't work by itself. I need the resistors to set the voltages at each pin to the correct voltage. It's called "biasing" If you google "transistor biasing" you'll probably get lots of useful information to review.

 

[thetmagic]

How can I make this more complex?