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Lie Detctor


Codyhtml
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Hello For the lie dector progect on this site i want to buy my parts at the local radio shack (closest stroe to me about the only store i think) and they don't have a 33k resistor could i use a 22k 10k and 1k in series? i figured i could and they don't have a 1.5k there would just a 1k work ? and they don't have a 1uF 16V Electrolytic Capacitor well they have a i uf but it is 50v would that work it is the closest thing to what it calls for that they have and for the trasnistor would about any transistor do such as une of these  last 4 transistors not the first on the page http://www.radioshack.com/category.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F002%5F017%5F000&Page=3
and instead of the meter could you use like a led instead ? thanks for help in advance
ps sorry for my bad spelling gramar etc.

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The series resistor it will work but is overkill .5k ohm may make adiference depending on what is that resitor is being use for, the cap question is the same what is it use for filtering? . My advice is www.digikey.com is cheaper, and  they have more parts

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With an LED you won't be able to adjust the "zero" setting very well, won't be able to see small changes in skin resistance like a meter, and the LED will be very, very dim even when the test person is sweating buckets!
Any small NPN transistor like a 2N3904 or 2N2222 will work with a meter in this circuit.

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ok looks like i'll have to use a meter but i still have a question about the capicitor just lookmat my first post and this isent important but is there anything that i can use instead of a meter i cant seam to find one at my local radioshack i know where i can get one but i won't be going to that store for a while

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Hello I'll Ask In case i wasent clear What About the capicitor i found a 1uF one that was 50v and i searched and even on digikey didn't have a 1uF 16V capicitor is there any Subsitute and is there any subsutitue for a meter i don't have a store that sells them with in about  a 1hour drive of me thanks

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The capacitor is used only to filter out local radio stations from being detected so just about any capacitor will be fine, 0.1uF, 1uF or anything in between.
The project's battery is only 9V and there isn't any input voltage so just about any capacitor voltage rating will be fine, 16V, 50V or even 1000V!

For an electronic meter you can use an LM3914 LED driver and 10 LEDs. It will be a voltmeter that you can feed with an opamp arranged as a current-measuring amplifier. It would need its own separate battery.

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thanks a ton i guess i'll go to my grandmas house sometime and pickup a meter on the way because i'm not in a big hurry and i'll garintee that the meter will be cheaper and eayser and i'm on a tight budget thansk for all your help you rock
[move]Audioguru is AWSOME :P :P :) ;)[/move]

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You must figure out whether the resistors get hot all by themseves, or because of current flowing through them. If it is because of the current flow, a 1/4W resistor and a 1/2W one that have the same value will both have the same current and heat the same. Therefore if the power dissipated by a 1/4W resistor is within 1/4W, don't you think that a 1/2W resistor would easily be capable of disipating only 1/4W or less?

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  • 2 weeks later...

you know what i'm so dumb i don't know like anything :( so sorry for asking so many questions and not being alot of help  :-[ any way how do i do the pot in the circuit i don't know what pins to conect where and stuff please help me and an audio taper pot won't matter will it ? i have a 5k audio pot will that work thanks

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Hi Cody,
An audio pot will work, but have most of its adjustment range crammed at one end.
It has only 3 terminals. The schematic shows to connect its slider, the middle terminal, to one end. Try it with the middle terminal connected first to one end, then try it with it connected to the other end.

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ok thnaks to this is what it looks like
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and try it with this atone end you mean at the end where it has the scigily resistor sign and the other thn where there is the dot try the middle wire? right and try it in bolth places right? thanks

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ok i think i could be alot less of a nucence if i could learn basic things like how to read schimatics good i can't figure out from my charts and tables how to read what pin of a transistor is EBR etc it just has the symbol but that isent a huge deal i tink i know how to figure it out now that i think of it but the pot is still giving me a hard time i'll post a pic because i still don't know what to do i'm just using aligator clips so i can change the middle pin
if he knob was pointing towards you the pin on the left above the one without the color was the one that was NOT marked with the squggle line and the other pin with color was conected to the squggily line how is the best way to try

post-5255-14279142179909_thumb.jpg

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Hi Cody,
A potentiometer (pot, or volume control) is a variable resistor. Its squiggley line is its resistance and its arrow is the slider that slides along its resistance part.
I have never seen your before but I think that its slider is the upper right pin. Connect it to one of the other pins and try it. then try it with its slider pin connected to the other pin.
Audio volume controls look like this in my country:

post-1706-1427914218051_thumb.jpg

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Any small NPN transistor like a 2N3904 or 2N2222 will work with a meter in this circuit.

If your transistor is a PNP it won't work in this circuit anyway. You might as well purchase a cheap one that is the correct type. RadioShack transistors are usually marked on the package which wire is which for people who don't have access to Google to look it up.  ;D

post-1706-14279142180588_thumb.jpg

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Or as there's only one transistor in your circuit you could just reverse the power supply polarity and the polarised capacitor and it would work fine with a PNP transistor.

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