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Troubleshooting lie detector

  1. Apr 22, 2005 #1
    I'm trying to build this simple lie detector (picture below). I'm 90% sure that i have it built correct on my breadboard, but for some reason my LEDS are getting destroyed if i try applying the full 9V. It takes around 3V to make the LEDS to turn on about halfway. For some reason, there is a lot of current going through this thing. If someone could draw the components on a breadboard picture for me that would be awesome. I just need to see if i'm building this right. Also, if anyone knows a good site that has a tutorial of the basics of breadboards i would appreciate that too.

    Attached Files:

  2. jcsd
  3. Apr 22, 2005 #2
    This "should" work.

    Attached Files:

  4. Apr 24, 2005 #3

    Alright thx! I owe you!
    I will be shore to reply once i test it out on monday!
    Last edited: Apr 25, 2005
  5. Apr 25, 2005 #4
    I tried it in class today and i'm 90% sure i set it up right. It doesn't turn the leds on at all. Can you double check the schematic?
    Last edited: Apr 25, 2005
  6. Apr 25, 2005 #5
    here is a picture of the circuit itself not on a breadboard if it helps

    Attached Files:

  7. Apr 25, 2005 #6
    http://www.iguanalabs.com/breadboard.htm [Broken]

    You're right though. It appears I drew VR1 to the collector of T3 but it should go to the b ase of T2. R1 and R2 are labeled backwards but that's inconsequential.

    The VR change should fix everything.
    Last edited by a moderator: May 2, 2017
  8. Apr 25, 2005 #7
    alright cool thx
  9. Apr 27, 2005 #8
    I switched the VR1 today and now my green LED comes on, but for some reason my red LED isn't coming on. I have tried applying lower resistances to the probes, but the red LED isn't coming on. Are all of the transistors in the right spots on the schematic you drew? If you could double check, i would greatly appreciate it.
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