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Digital Outputs / Logic Chips / Ic's?

Discussion in 'Microcontrollers, Programming and IoT' started by chris57828, Mar 21, 2012.

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  1. chris57828


    Feb 10, 2012
    Can someone help?
    I have a USB integrated circuit interface board along with a breadboard with a 5V supply. I have set it all up; pull up resistors, resistors the lot. The interface board only has 8 digital outputs though.

    I wanted to increase the outputs as my main aim is to simulate a traffic light junction using LED’s and a breadboard so on the advice of somebody I bought a 4:16 decoder (74154 logic chip). This chip has four data select lines, is binary weighted and has 16 outputs, the only problem is only one output can be low at a given time; this is useless because there are far more phases than two on a traffic light junction.

    Can somebody tell me what logic chip has about 16 outputs where the outputs are not mutually exclusive, so I can have any number of outputs at either 1 or 0 at a given time, depending on the binary weighted input I select on the USB board?

    I know this is a difficult one!
    Thank you.

  2. GreenGiant


    Feb 9, 2012
    you are asking for 4 inputs (total of 16 possible combinations) to control 16 outputs (with 255 possible combinations), that is not possible to do without a(another?) microcontroller

    Your best bet would be to either control some of them in parallel with each other.

    Can you go into more detail about what you want the traffic lights to do or describe them more (like how many lights, timing, etc)?
  3. chris57828


    Feb 10, 2012
    I am prepared to buy another chip.
    Yes, there will be 16*16 combinations, however, in reality I won’t be able to make use of most of them as on a simple crossroads with pedestrian lights very few lights will be true at any one time else the consequences will be fatal.
    Originally I am going to start with a simple crossroads with twelve lights, red green amber for northbound, red green amber for southbound, red green amber for west bound, and red green amber for eastbound.
    For example, the green on both north and southbound will on at the same time as traffic abiding by the rules should not collide and as it is only a simulation these LED’s can be daisy chained!
  4. GreenGiant


    Feb 9, 2012
    so you have 12 lights, but you only actually need 6 outputs

    3 for north/south
    3 for east/west

    as you said both north and south will be green at the same time, using that I deduce that they will also both be yellow and red at the same time, rather than have a separate pin for each way. Same for east and west, this also leaves 2 pins open for use as left (or right depending where you live) turn

  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Another option is to connect one or more 74HC595's to three of the outputs and bit-bang values into them. You can effectively have as many outputs as you want by cascading the 595's.

    See here.
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