Police Timer Help

Discussion in 'The Projects Forum' started by SimpleCircuitMan, Jul 3, 2014.

  1. SimpleCircuitMan

    Thread Starter New Member

    Jul 3, 2014
    4
    0
    I've recently built a police timer circuit, The link for the circuit, supplies and a videos is below.

    - http://www.555-timer-circuits.com/police-lights.html

    The problem I'm having is not its functionality, but the output is about 1.0v-2.5v as a pulse. i need a way to bump up the voltage to 12v so I can use LED strips. Ive tried to play with 3904 NPN transistors but I cant seem to get it to work, I've thought about using solid state relays but they are a little big for this application. I went to an electronics place and they said maybe use a SCR (Silicon-Controlled Rectifier) Please tell me your thoughts and suggestions!

    Please help me out, post a comment or message me, Thanks
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,140
    1,789
    You are saying that with a 9V battery you are getting only 2.5V out of the 555 on pin 3!!?? If so you are doing something very wrong.

    Replace the 9V battery with 12V and hook up the 2N3904 just like the BC547 and you should be good to go. You tried that -- Right?
     
  3. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    That would be the output on the 4017 Decade counter is dropping down to 1.5Volts?

    Make certain that all of the diodes in your OR outputs are in the correct polarity so that you aren't backfeeding from output to output as they each transition from low to high.

    Link us to a data sheet for the LED strips. You might need heavy amp transistors.
     
    SimpleCircuitMan likes this.
  4. panic mode

    Senior Member

    Oct 10, 2011
    1,320
    304
    1)
    4.7k for LED current limiting is to high, you are limiting LED current to 1.3mA. this requires use of high efficiency LEDs, standard LEDs will barely light up. you may want some 15-20mA so those resistors should be 390-560 Ohm. even better, connect both LEDs in series and use single 150 ohm resistor. this will also reduce current draw and extend battery life.

    2)
    since collector current is not more than 40mA, base current does not need to be more than 4mA. this means that base resistors (470 ohm) could and should be higher, about 1.5-2.2k should be better.

    3)
    if you are using efficient LEDs, there is no point in using transistors, 4017 can drive them directly
     
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  5. SimpleCircuitMan

    Thread Starter New Member

    Jul 3, 2014
    4
    0
    Thank you everyone for the advice, after a couple of hours of messing around ive finally got it! Thank you Agian!!! :) :) :)

    Sorry bout that... maybe not
     
    Last edited: Jul 4, 2014
  6. SimpleCircuitMan

    Thread Starter New Member

    Jul 3, 2014
    4
    0
    Now able to run 12V

    Input Voltage IS 12v
    The voltag on the LED strip is reading 7v
    -out of the 555 is reading 10.95v
    -out of the 4017 output pins reads 0.8v
    -out of the diodes reads 2.26v
     
  7. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    What is the exact part number for your 4017?

    There are some parts, types meant to work in TTL circuits that won't work with 12V.
     
  8. SimpleCircuitMan

    Thread Starter New Member

    Jul 3, 2014
    4
    0
    MC1407BCP
    5AE1224G

    This is what's on my 4017's, Yes I bought two and they both work
     
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