>>My application is a Harness Continuity Tester, and I use the CD4051B
>>mux/demux for the test points. Most of the harnesses tested have
>>connectors, but sometimes they have bare terminals, or it is assembled
>on the >test board, so people are constantly touching the terminals, and
>these are
>>directly connected to test pins which are connected to the test
>>points, which are CD4051s pins. So basically that's what I am doing...
>Now
>>some backup to support why I did this...
>>
>
>        I'm on the Coast Starlight train right now, so I can't look up
>the 4051... but does it have clamp diodes?  If so, the series resistors
>should add a lot of protection.  Resistor valuse would depend on circuit
>speed.  I seem to recall a maximum suggested input series resistor value
>in some CMOS databook somewhere.  Maybe 10K to 50K.  Also, I'd probably
>use SIP resistor packages... a lot smaller than DIP.
>        Your cable harness tester is an interesting project.  I designed
>one but never built it (maybe some day).  I just used a bunch of shift
>registers, some parallel out (like the UCN5832), some parallel in.  These
>were then all in series and hung on the parallel port of a DOS computer.
>A DOS program would "learn" what a good cable was and store the file.
>All other cables are compared to this file.  The 5832 just grouned one
>pin at a time while the parallel in shift registers watched what happened
>at the other end of the cable.  This only required a 4 wire interface to
>the PC (data to shift register, data from shift register, clock, and
>load).  It seems like the 4051 would require quite a few more I/O pins.
>Is there some specific reason for going with it?


Well, yes.
Shift registers was one of the options I considered when I started with this
project, but there are certain advantages over shift registers:
    Speed. Depending on how you do the tests, shifting a lot of bits thru a
long chain of shift registers can be slow. But by using the muxes, I can
check several pins at the same time, and after finding continuity, just
check a few options to find the pin with continuity.
    Special tests. Splices, for example is a type of tests done more easily
than by using shift registers.
    Bidirectionality. The 4051 can serve as inputs or outputs, so I can make
any test point an input or an output.
    Price. I am not sure about the shift registers, but the 4051 is cheap
and readily available from several manufaturers.
    Low power. Being CMOS, they consume very little power, and this is one
less issue to worry about whan using a whole lotta ICs.

There may be more issues I can't remember right now.

Gabriel

>
>
>
>Harold
>
>
>___________________________________________________________________
>You don't need to buy Internet access to use free Internet e-mail.
>Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
>or call Juno at (800) 654-JUNO [654-5866]