Milk

Can anyone be so kind as to explain the lie detector project?

http://www.electro-tech-online.com/viewtopic.php?t=43

I really have no idea how you use it or what the parts are. :?
If someone could throw together the exact parts I will need and explain how to use the thing (perhaps a quick explanation of how everything works a little more thoroughly), I would greatly appreciate it.

Thanks in advance

grrr_arrghh

its quite simple really

not sure about exact parts - I suspect that it doesn't matter that much - its quite a simple design. My best guess would be 1Ks for the resistors and 1uF for the caps.

the component marked 'M1' is an ammeter.

Bassically, when you lie, because of various factors, you skin resistance goes down. So you place the electrodes on someones skin, and if they lie, the resistance accross the electrodes will change, and the ammount of current flowing through the ammeter will also change, and the needle will move dramatically (hopefully). This movement shows that they are lying. The variable resistor is to adjust the sensitivity, and some people may have different natural resistances, and some adjustment may be needed.

Does that help at all?

Tim

Milk

Yeah, thanks that helped alot, but I still have a few more questions. Do I need to get 2, 4.5v batteries, or can I use a single 9v in some way? Also I'm a little confused as to what that arrow pointing to the R2 on the schematic is. The final question is on the Q1, how do I know the difference between NPN PNP, I know the schematic shows NPN, but what's the difference, and are there actually seperate transistors or if is simply the way you utilize it.

Thanks again

andrew2022

resistor with an arrow is a potentiometer (variable resistor)

Milk

This may be really stupid questions but
(1) The potentiometer has 3 prongs on it, 2 in the back and 1 in the middle front, how do I install this for this project?
(2) Which way does the transistor get placed in? one side is larger and one side is smaller on the head, which faces which way and what not?

Thanks again :?

vaineo

The two in the back are the top and bottom pin in the picture and the one towards the front would be the pin that connects to the top in the schematic.
It depends on the particular transistor your using. If you have Adobe Acrobat Reader just goto google and type in the transistor part number and look for a PDF file in the search results. This will most likely be the data sheet. http://www.ligo.caltech.edu/~vsanni/...BJT/2n2222.pdf Thats an example of a datasheet if you havn't seen one before. It'll tell you the orientation of the pins.

grrr_arrghh

:?
basically, the middle pin (or the pin thats out on its own) on the potentiometer is the one with the arrow on it (on the diag). The other two pins are the other two pins - i.e. it doesn't matter which way round they go.

There is a difference between PNP and NPN, both in the way they are made and what they do. So if the diag says NPN, you need NPN.

as long as the batteries are the same, it prob doesn't make much difference what you use - two 1.5v may work instead. As for one battery, have a quick look at http://www.electro-tech-online.com/v...755&highlight=

does that help at all?

Tim

Milk

A lot, thanks again