Lie Detctor

[Codyhtml]

ok i'll try that thanks

 

[Codyhtml]

ok i thought i had a parrt that i didn'y so i had to use a different transistor and i'm not sure how to tell if it is pnp(i doubt it is ) and what its EBC are because i saw how different transistors have different EBC so i need more help again

 

[audioguru2]

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.  ;DView attachment 36816

 

[Codyhtml]

well mine isent a pnp i'm almost positive but mabe i will pick one up from the shack  monday but i don't know what to look up on google anyway

 

[Alun]

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.

 

[Codyhtml]

ya but my problem is i don't know what my transistor is

 

[Alun]

Look at the part number do a google search, type in "part number" datasheet, if that doesn't work ask a question in the datasheets section of this forum.

 

[audioguru2]

I looked at the datasheet for the transistor I recommended in Google, and I found all kinds of important information that you need:

View attachment 36817

 

[Codyhtml]

ok i got info on my transistor and soldered it in i hooked up the pot and it workes ether way it just reverses like you have to turn it left with it hooked up one way and turn it right hooked up the otherway but i checked ind i  can't find any shorts i thinght that would be the problem it dosent work i can't get it to drop below .6 millamps and then if i put the electrodes on and have sombody lie or somthing it dosent change even if i touch the electrodes toghter without a person so i don't know i bad cap wouldent be the problem a reversed or bad cap and it wouldent be a problem eith the transistor would it or is there probably a short and i just can't find it sorry for asking so many questions most of you guys could build this in like 1 day with parts from your junk box but i guess i'd never learn and be able to help other people later if i never got help

 

[audioguru2]

Hi Cody,
The transistor isn't working or the batteries aren't 4.5V. The schematic shows a longer line for the positive terminal of each battery cell. Each of the two batteries are 3 cells and they could be AA cells.
With nothing connected to the electrodes the meter should try to go backwards between 0.7mA and 3mA depending on the setting of the pot.
With the electrodes shorted together, the meter should read between about 2.5mA (full scale for a 1mA meter) to backwards 3mA, adjusted with the pot and should be able to be zeroed. It should do the same if the capacitor is shorted.

 

[Codyhtml]

well the baterys are a 4 case with one of the batterys replaced with a wire to have a 3 cell case and the transistor should be good hmm wait i think i rember what i did never mind i think i made a mistake i'll post if it works when i correct the mistake

 

[Codyhtml]

i guess it must be a bad transistor

 

[Codyhtml]

sorry for double post but i realised mabe that kind of transistor won't work with this project it was a 2n5014 or somthig i'll get a new one that will work some time when i go to the store