[sdiy] Four bit to serial translator

[Scott Gravenhorst]

music.maker at gte.net wrote:
>You want to know if any bit or bits of a 4 bit word changes.  Well, A
>differentiator will create a pulse, but for a 1 to 0 transistion, the pulse
>will be negative and for a 0 to 1 transition, the pulse is positive.  So the
>differentiator for each bit should have two diodes, one for the positive
>pulse and one for the negative.  

Oops, one too many resistors.  Here's the revised idea:


                  to other bits
                       |
         From          |
        Other ->|-+--R-+
         Bit      |    |
                  R    |
                  |    |
                 gnd   |
                       |       |\        +-->|--Vdd (CMOS)
            +-->|--+---+-------|+\       |
            |      |           |  >-+----+----o Pulse Out
            |      R        +--|-/  |
            |      |        |  |/   |
            |     gnd       |       |
            |           +---+--R----+
            |           |
            |           |
            |           |
BIT ----||--+--|<--+-R--+
                   |    |
                   R    |
                   |    |
                  gnd   |
                        |
                        |
         From -|<-+-R---+
        Other     |     |
         Bit      R     |
                  |     |
                 gnd   to other bits

>Probably good to use a CMOS buffer to drive this.  
>The R represents a resistor, they are not necessarily 
>all the same value.  I think this would use 2 ICs at most, 
>No transistors, 4 caps for the differentiators and 8
>diodes.  Fewer resistors than 52...  looks like 4 per 
>bit plus 2 more for the opamp gain control stuff.  
>Something like 18 to do this for a 4 bit word.  The caps
>and resistors to ground after the diodes would control 
>the width of the pulse.
>
>Peter Grenader <peter at buzzclick-music.com> wrote:
>>Guys and gal,
>>
>>I'm in a bit of a pickle and it's getting sour here - thought you cold throw
>>me a life raft. 
>>
>>I've added an asynchronous VC to Milton.  Quite the bomb.  It doesn't give
>>two sheets what the incoming pulse is doing, or even if there IS an incoming
>>pulse for that matter - when the VC input's A to D changes state, the
>>counter immediately reacts.  With this you can now set the start and end
>>step to wherever you want, plus achieve some amazing non-linear
>>progressions. Driving it with a sine wave being particularly interesting as
>>the sequence accelerates at both ends.
>>
>>Problem is, as the name implies -  it's asynchronous. It functionally
>>remains a bit of a lame duck as there no way of syncing anything to it.  So,
>>unless you're planning on a legato glissandi, you're screwed.
>>
>>I've worked out a way to extract a timing pulse, but its involving more
>>parts than I like, and I'm certain there's an easier way.
>>
>>What I need is a short pulse each time the 4 bit word changes.  I tried just
>>monitoring the LSB, that works until it jumps to another of the same parity
>>and then it's lost.  I tired doubling the speed of the LSB to synthesize it
>>and that was totally the wrong direction.  I've thought through parity
>>comparators, but again, that leaves holes.
>>
>>So what I've ended up doing is taking the outputs of the 4050 (all sixteen
>>of them) and shaping those into pulses rather than gates and summing them
>>into one continuos stream, each with a 50ms on time.
>>
>>Although it took only one sentence to describe it, that function requires
>>sixteen transistors, 52 resistors, 22caps and 5 ICs.  In short - forget it.
>>
>>Any competent PIC programmers out there who are up for a challenge?
>>
>>If nay - anyone have a CMOS logic level solution???
>>
>>thanks in advance,
>>
>>Peter

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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