What could be wrong with my led light box?

Hey you guys I did everything correctly but its still not working. Here's a pic of mine. I know its not the leds because they light up when I plug them up to a 12v source.Also thats a brand new tip31 and im using 8 Triple A batteries?

Picture of What could be wrong with my led light box?
iceng11 months ago
Re-drawn and if 12V battery that 100 ohm resistor increases to 350 ohms.

With the darlington  configuration a 1uF capacitor in series  with the signal will also work !

tramont (author)  iceng11 months ago
do i really ned to buy another transistor
iceng tramont11 months ago
No you don't, but do follow steveastrouk's advice !

You non-EE people should know how we buy parts.
  • One to Smoke
  • One to Lose
  • One to Use
  • One for the second version
  • One for another reason
  • And add 10% for good measure
Get at least SIX next time.
tramont (author)  iceng11 months ago
Okay but does he want me to put a 100ohm resistor on each led? Also how would I go about wiring that up
iceng tramont11 months ago
Here is the circuit that Steve described.
a gain.gif
iceng iceng11 months ago
Oops one correction change the 47K to a 4.7K ( yel-viol-red ) resistor
tramont (author)  iceng11 months ago
Im only using 6 leds, so is it still wired the same?
iceng tramont11 months ago
Which six ? ...... :-)
a6 gain.GIF
Why are you using a 40 watt transistor when a 2N3904 1/2 watt will do?
Also you need resistors you may have connected this up and the LEDs flashed once and died from to much current.
And he only acquired a single one ! ...................... :-P
I buy from here,

I can get 100 transistors for the same price as five at Radio Shack.
steveastrouk11 months ago
Diodes in backwards ?
No base resistor ?

Take a resistor (4k7 will do), and connect it to the base of the transistor and the 12V supply. The LEDs should light. If they don't, mak sure they are the right way round. If they STILL don't light, you have a dead transistor.
iceng steveastrouk11 months ago
+ you may have too many LED in series and a transistor forward forward drop to light up.
steveastrouk iceng11 months ago
Hmm. Yes, 6, and on 12V.

Try 3 in parallel with 3 and put a 100 ohm series resistor in each leg
tramont (author)  steveastrouk11 months ago
Okay im going to try that thanks for your help
iceng11 months ago
(removed by author or community request)
steveastrouk iceng11 months ago
Wot, no current limit resistor ?
iceng steveastrouk11 months ago
Late night muddy brain non-engaged :-)

Get More Out of Instructables

Already have an Account?


PDF Downloads
As a Pro member, you will gain access to download any Instructable in the PDF format. You also have the ability to customize your PDF download.

Upgrade to Pro today!