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'Using a PIC in a harness checker'
1998\06\09@141422 by Steven Kosmerchock

I have been asked to design a harness tester that will check 24 wires. They want
it to have a LCD  that will either display "FAIL" or "PASS". Does anybody have
ANY suggestions. They would be greatly appreciated!!!! As you can tell, I'm not
a PIC Guru.

               Best regards,


1998\06\09@181431 by Janet and Carl McIver

   Try a multiplexer to drive one wire at a time and then a demux to check
the other end.  If the input code equals the output code, pass it on to the
next guy.  24 wires will require a couple multiplexers, as no single
multiplexer has 24 outputs that I know of.
{Original Message removed}

1998\06\09@184741 by gwaiche

picon face

If your main concern is the I/O pins need, then you can use
3 chained shift registers (8*3) like the 74HCT165 to read
states in your 24 wires. It won't use more than 3 pins...


Steven Kosmerchock wrote:
> Friends,
> I have been asked to design a harness tester that will check 24 wires. They wa
nt it to have a LCD  that will either display "FAIL" or "PASS". Does anybody hav
e ANY suggestions. They would be greatly appreciated!!!! As you can tell, I'm no
t a PIC Guru.
>                 Best regards,
>                 Steven
> email:

1998\06\09@204509 by Calvin


Been there, done that (actually doing it).

We have been commercially producing 48 and 96 circuits harness testers for
about two years now.

I know it sounds real easy, but depending on what you need it may not be so
(what about crossed wires, opens, shorts and splices?). We learned this the
hard way. I have worked for several years in harness factories as a test
equipment engineer, and we have studied all the major commercial testers
(Cablescan, Dynalab, etc.) to see how they work (no reverse engineering

I may be able to give you some pointers.

Is this going to be a commercial project? (are you getting profit out of

You can contact me thru my e-mail address at:

Gabriel Gonzalez
TGO Electronica

{Original Message removed}

1998\06\09@212018 by Michael S. Hagberg

don't just say 'pass' 'fail' tell which wire failed and if it failed open or
closed, maybe send a report to a local serial printer with the corrections
to make. ie like 'Connector 4, move pin 3 to pin 4'

you could use the same chip i just mentioned
UCN5833A to drive each line high or low and then serial shift the inputs to
verify the wiring.


{Original Message removed}

1998\06\11@174952 by Thomas McGahee

Here is how I have done this in the past:
You have 24 wires. You have to inject a signal at one end and
test for its presence at the other end. The most sane approach to the
hardware is to use three 74164s as a 24 bit serial to parallel
OUTPUT port, and three 4051s as a selectable one-of-24
multiplexer. The final single input line should have a 10K
pullup resistor on it, so that if a line is OPEN the resistor
will cause the PIC to see a HIGH.

Since sometimes a harness will have LESS than 24 wires, it is
useful if you allow the user to initially choose which wires are
to be actually tested. Error reporting/checking can then be suspended
on these wires. Pushing a button causes testing to commence.

You reset the string of 74164s and then read in each
of the input multiplex bits one at a time by outputting the
proper "address". If any are NOT low, then that particular line
is OPEN. Report on errors as they are found, or save the info
in a ram variable bit location and report on errors later.
I always send out the information in the form: pin#, error type OPEN.

Test proceeds by clocking in ALL "1"s to the 24 bit serial output
port. At this time all input scans should read "1"s.

Now clock in a SINGLE "0". Check all inputs. Only one should match.
And that should be the CORRECT one. If not, report the error in the
form: pin#, error type SHORTED, shorted to pin(s) pin#(s)
Note that there may be multiple shorts between wires, and so the error
may get reported more than once.

Keep track of error count.

Shift the test "0" bit and check all lines again. Continue this
process until all 24 lines have been tested by shifting the "0"
through all 24 positions.

When checking, allow time for the wire capacitance to be charged.

When all lines have been tested, if there are no errors, display
message "PASSED". If there were any errors, display message
"FAILED" and allow the user to step through the errors by pushing
a button.

You can add a sound output bit to the design, if desired. Use
different tones to indicate PASS/FAIL, and the user doesn't even
have to look at the display!

Add bells and whistles as desired.

Hope this helps.
Fr. Tom McGahee

> {Original Message removed}

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