Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help with Monostable Circuit

  1. Sep 10, 2012 #1

    I am trying to make a Monostable circuit with my 12V LED strip. When I push the switch once, the LED strip will light up for 10 seconds and go off by itself. I have built the circuit using this schematic, the only difference is I am using a 1000uf capacitor.


    Everything works, but the only problem I have is the 555 timer can only output 200mA, so the LED strip is very dim. I understand that I could use a TIP31C NPN transitor to amplify the current? What I did was wire the base to pin 3, the collector to the negative pin of my LED strip and the emitter to pin 1(ground). THe LED doesn't light up at all.

    I am not really an expert in electronics, I hope someone can help me. Thank you.
  2. jcsd
  3. Sep 10, 2012 #2


    User Avatar
    Science Advisor

    Do you have the LED anode connected to the battery positive?

    Also, you should place a resistor in series with the base to limit the current. The transistor BE junction is approximately a short circuit on the 555 timer output.
  4. Sep 10, 2012 #3
    Hi uart,

    Thanks for your reply. The positive is connected to the 220 resistor and to pin3. I have attached a 3D view of the circuit. The LED strips appears to have resistors on them.

    I'm currently blurred trying to get this to work, I will have to look at the resistor part when I solve this. Been looking for a solution for days..
    Last edited: Sep 10, 2012
  5. Sep 10, 2012 #4


    User Avatar
    Science Advisor

    You need to post a circuit diagram of how you actually have it connected. Otherwise this is futile.
  6. Sep 10, 2012 #5
    Issue solved.
    Last edited: Sep 10, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook