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BCD to Binary Conversion

Discussion in 'Electronic Design' started by K Wind, Sep 15, 2003.

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  1. K Wind

    K Wind Guest

    Let's say I have a couple of BCD counters (CD4510) with thumbwheel switches
    connected to the preset inputs and a couple of binary counters (74193)
    sharing a common clock with the 4510s. If I initially reset all counters,
    preset the 4510s and count down to zero while having the 74193s count up,
    have I converted the numbers indicated on the thumbwheel switches to binary?
    It seems like this would work, but would like input from others.

  2. K Wind

    K Wind Guest

    Thanks for the info.

  3. I think you might add that it will work as long as the pulses are clean.
    No pulses too short for the CMOS counter, nor too low for the CMOS
    threshold, which is being clocked in parallel with a TTL counter, nor
    any noise that might trigger the TTL.
  4. If we start adding caveats we might be here all night, but it's
    perhaps worth noting that those CMOS CD4510 parts are glacially slow
    at 5V (2MHz). Not much drive either, so using HC193's might be an

    Best regards,
    Spehro Pefhany
  5. K Wind

    K Wind Guest

    Thanks for the info. The clock would be around 10KHz to 100KHz and made of
    CMOS inverters or a 4093. The maximum number of counters would be four each.
    I haven't looked at any specs on how many TTL devices can be driven by
    whatever device would be used for the clock, but will when the time comes. I
    will also look at what is required by the 74193s.

  6. K Wind

    K Wind Guest

    In this application, I won't be driving anything with the 4510s. All they do
    is determine how many clock ticks are sent to the 74193s. I will be
    monitoring the "carry in" to determine when all the 4510s have counted down
    to zero and then shut off the clock. Both the 4510s and the 74193s will be
    have a common clock. Whatever I use to implement the clock will have to
    drive all of the counters.

    I must confess that I am on a very tight budget here and have to use what I
    have on hand. I do appreciate, however, all of the ideas put forth. Keep
    them coming.


  7. Okay, salvage an EPROM, 2716, 2732, whatever has a window so it can be
    erased and is 5V only, from an old computer or whatever, borrow an
    EPROM eraser and a programmer and use a hex file something like this
    one to burn the EPROM, after erasure, of course:


    Use output bits 0..6 as the binary output (0 to 0x63) and bit 7
    indicates an invalid BCD input (0= okay, 1= error). Address lines 0..3
    go to the LSD and address lines 4..7 go to the MSD thumbwheel. Tie the
    unused address lines to Vss.

    Best regards,
    Spehro Pefhany
  8. K Wind

    K Wind Guest

    Thanks. I'll take a look at what I have.

  9. Strictly speaking, those CMOS outputs can barely drive a single TTL. If
    you want to use counters (rather than an EPROM) and drive them from CMOS
    it would be best to use all CMOS counters, like HC190 and HC193.
    Otherwise you should buffer the clock before it goes to the TTL. IOW
    the clock generator would drive the CMOS counter, and also drive a CMOS
    buffer, and the buffer would drive the TTL clock.
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