1 input, 4 outputs switching at diff Frequencies

Discussion in 'The Projects Forum' started by Daemon, Jun 20, 2009.

  1. Daemon

    Thread Starter Active Member

    Jun 20, 2009
    Hi all

    I am new to the forum and would like some suggestions and help with a circuit. It needs to only be a few components.
    I want an ic that can switch 4 outputs based on different frequencies. Does such a thing exist?

    Background. I computer control christmas lights. The strings of lights are usually chopped off and thrown in the bin and each of the 4 functions which are shimmer, sparkle etc(I am sure you have seen them) are then attached to a seperate channel of our christmas controllers and from that day on controlled via the computer.

    What I hope to do is retain the controller and introduce a 4 output switch so I can send a different frequency signal to the controller and switch 4 different functions.

    I dont know if its even possible but I thought I would give it a try.

    My computer controller is capable of dimming each channel to 192 levels. I assume it does this with differing frequencies so what I hope is to introduce my circuit into the equation so 1 frequency will trigger one function and a higher frequency will trigger another function and so on.

    Can someone get me strated by answering either of 2 questions.

    1. Is there a low cost ic that can switch at different frequencies without needing a programmable ic, or a similar arrangement that will do the same job as an ic.

    2. Does the dimming only rely on differing frequencies or is the more to it?

    Thanks and hope to get a response.
    Great site by the way, it is modelled exactly like several others I use so I can easily find my way around.

  2. mik3

    Senior Member

    Feb 4, 2008
    Dimming relies on PWM except in special cases where varying frequency is used.
  3. Daemon

    Thread Starter Active Member

    Jun 20, 2009
    I looked into it a little and the dimming method being used is called phase angle(controlled) dimming and relies on finding a zero crossing signal of the ac current to determine when in the phase the ac signal is.
    A 5v dc signal is then sent to an optocoupler(at varying frequencies I assume according to the dimming level) and the optocoupler activates a triac which connects the inductive load which in my case is 24 volt.

    What I need to know is the mechanics of the dc signal that is sent from the controller after it has found the zero crossing point and if there is a component I can add that will switch the 8 function controller.

    I am still researching the controllers to find out how they switch.

    Cheers for the reply.
  4. BillB3857

    Senior Member

    Feb 28, 2009
    If you get a DTMF decoder you can get 7 outputs that are dependent upon 7 different frequencies. These decoders are used on tone dial telephone systems. You can control the channel on or off with one leg of an AND gate the dimming function from your computer to the other leg. The output of the AND gate would then feed the same line your computer is feeding now. I guess my question would be, "If you are already using a computer to control the lights, why add another layer of complexity?"
  5. Audioguru

    New Member

    Dec 20, 2007
    A dimmer for incandescent light bulbs uses a very simple circuit using the phase angle and a triac switches the pulses. You don't notice the incandescent light bulb flickering at the mains frequency because it takes time to cool in between pulses. It is a form of Pulse-Width-Modulation but at the low frequency of the mains frequency or double the mains frequency.

    A light dimmer uses a potentiometer to control the phase angle. Your circuit uses DC to control the resistance of an opto-coupler to control the phase angle.
  6. Daemon

    Thread Starter Active Member

    Jun 20, 2009
    It's a channel restriction. If I can do what I hope to then I dont need to use 4 seperate channels to drive 1 light set. Does that make sense? Why just chop off a controller that performs perfectl adequate controlling and use 4 channels to do what you could acheive through only 1?
    I can still do the functions on the lights but need 4 of my channels to do what I want to do with 1.
    I will look into what you have suggested and see if its workable.
  7. Daemon

    Thread Starter Active Member

    Jun 20, 2009
    How the 8 function controller works is that there is firstly a bit of a bridge rectifier to convert from ac to dc and then a resistor to drop the voltageto about 5v which then goes to a 14 pin IC which is marked LS-11S usually or a different design has a small daughter board which I assume does the same function. There are also four SCR's or triacs and the push button that grounds one pin of the ic to change the functions.
    I cant find any info on the LS-11S but what I hope to do is replace the LS-11S with an ic thatcan changethe function at different frequencies.

    The DTMF decoder lookstoo large to accomplish what I am after.

    When dimming with phase angle dimming anything below 20% is usually a waste of time so I wanted to use say 1-4% dimming for the first function on the controller and 5-9% for the next and so on and then use 20% and up for the functionthat has all the lights on and then hopefully from 20%-100%dimming could also be applied to that one functionso the lights could be dimmed to different levels in a steady state but by sending a lower frequency also activate the other 7 functions.

    It is just a matter of finding an integrated circuit suited to the job.