Hi dragster73,
Yes,
i think i follow what you have in mind,
For some reason you are keen to have a number displayed.
I am kind of thinking along the lines of two 4514B ttl
chips, they also make them in cmos, but for home
constructor use, i think the sturdier ttl variety is
preferable to the easily damaged cmos type.
They also do it in a package with flying leads, but for
this i think the standard Dual-Inline-Package with 24
legs would be fine.
They are a De-Multiplexer chip, with 16 individual out
pins, and 4 bit binary input.
Using two of them should give 32 individual output
points.
The binary input section carries a latch.
I am assuming you are conversant with putting
together assemblies using chips.
See here for a pic of the 4514B chip
**broken link removed**
**broken link removed**
**broken link removed**
The suggestion is to run a free running oscilator fairly
slowly say about 6 c.p.s. and feed a binary 5bit counter
with it to get a 5 bit output A, B, C, D, E, to run
through the 5 binary outputs at about every 5 secs
roughly.
The 5 bit binary output would be used to drive the two
demultiplexers, using the 5th bit to switch between
the two, to give a 32 way rolling output signal,
Also this 5 bit binary count would go to a counter
section made to drive two 7-segment displays.
This arrangement would refer each of the 32 outputs to
the same count on the 7-segment display pair, which
would not be showing, it would be 'Dimmed'
In the event of an output encountering an earth fault,
the 7-segment display would 'Bright-Up' for about a
quarter of a second. If thats the only earth fault,
the same number would bright-up every 5 secs or so.
If two or more earth faults are present, then the
display would show each, as it occurred.
I'm trying to see an easy way to make the display stay
until the next signal, which may be the same number,
if its a different number, i'm wondering if it could
be made to change and display the next number.
This would get a bit silly if there were too many
numbers, but i think a repeating display of a few numbers
might not be confusing, if its not to fast so they are
each legible, i guess it would be unlikely to be more
than two anyway.
Just figuring out which way round the diodes would go
has worn me out! ive shown the 28 way as a 32 way, that
doesnt matter, the extra ones wouldnt show as earth
leakage.
In the diagram presented here,
i have assumed 32 wires going out to the unit to test,
each being a possible earth fault.
They are each in turn presented with an output from
a 4514B chip, with no interval in between each.
Where each outgoing wire has no earth fault,
then the base of the associated transistor will see
a high level, typically 90% of supply voltage, in this
case 5 to 6 volts, being supplied by the outputs of
the two 4514B chips.
The outputs giving a 'High' each in turn, with almost
no discernable gap between each taking its turn.
If however, one of the outgoing wires has an earth
leakage problem, then when that particular wire has
the voltage presented to it via the resistor from
the output of the decoder(4514B) it will show up.
It will show up because it would not go 'High' like
the others, and the transistor would operate.
The diode in the emitter may not be needed,
its only in case the 'High' is not high enough to
shut the transistor, but it usually is.
When the transistor operates, it puts a supply to the
7-segment displays, or maybe the Ch.En on their drivers
i havent got that far yet .....
If you think this approach is worth considering,
i will try to finalise the set-up.
It will involve a bunch of chips, and a bunch of
diodes, and a bunch of resistors.
The diagram is far from finished,
and someone else may well come up with a suggestion
that is more to your liking.
It mainly shows the arrangement for discerning an
'earthy' wire, which is the main difficulty,
as i see it.
Best of luck with your project,
John