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'16F84 Port Expander'
1998\07\25@090502 by bill bass

picon face
Hi, all,

Being new to PIC and interfacing, I have a question for
PIC members.  Please help.

I am making a 6-digit 7-segment (common anode)LED counter and have
breadboarded the 6x4094 serial-to-parallel chips.  All seems working
fine except I have exceeded the current sinking capacity of the 4094s.

I am looking for alternatives to replace the 4094s.  The 74HC595 looks
like it can source and as well as sink 8mA current comfortably.  That
means I can use either common anode or common cathode displays at
will.  Personnally, I like to use positive logic where I don't have to
complement the output byte.

Can somebody please comment on this approach?  Is there a better way
of doing other than what I have said?

Hopfully I can wire the circuit up again this weekend and have a
couple of beer after! Thanks to all.

_________________________________________________________
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1998\07\25@101229 by Thomas McGahee

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face
Bill,
The 74HC595 will allow more current drive than
the 4094. Whenever I am in doubt about some point of
interfacing, I just throw together a test circuit.
In your case, just wire a 74HC595 to a breadboard
and use 8 resistors and a display. You can wire
the input high/low and clock in the segments and
see how she looks. You want the intensity of a segment
to be the same whether there is just one on, or all of
them on. (include the decimal point).

*****

It looks like you are running your six digits in
mon-multiplexed mode. You could switch to a
multiplex mode and then get by with just two
4094: one for the segments and one to control
six transistors used for digit select. Due to
the limited source/sink ability of the 4094 I
would suggest using a bare 4094 as a 'true'
level segment driver (1=segment on) with a current
limit resistor for each segment. Drive the
npn transistors as common emitter amplifiers
via a base resistor. This would mean using common
cathode LED displays. Cathode drive logic is
'true' (1 out from PIC makes transistor turn on).

You can eliminate the six transistors if you
drive an open-collector hex inverter such as the
7405/7406. That also eliminates six base resistors!
The 4094 can easily drive the 7405. This is a much
lower-cost solution.

Multiplexing will help keep the current consumption
low, but at the expense of a little software to
handle the multiplexing.

Hope this helps.
Fr. Tom Mcgahee


----------
{Quote hidden}

1998\07\25@101437 by Morgan Olsson

picon face
I did exactly that.

I even omitted the series resistors, and instead used a trimmable low
voltage supply regulator for the HC595 chips and set it so the voltage
resultet in the correct current with only the resistance of the drivers and
LEDs regulating.

I think i used about 20mA per segment, but check different manufacturers
datasheet, the maximum ratings vary!

I was afraid of deviation in current and light due to varying resistnace in
display segments and HC595 chips, but could not notice any.  :)



At 05:53 1998-07-25 -0700, you wrote:
{Quote hidden}

/  Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \
\  mrtspamKILLspaminame.com, ph: +46 (0)414 70741; fax +46 (0)414 70331    /

1998\07\25@102938 by paulb

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face
bill bass wrote:

> I am making a 6-digit 7-segment (common anode)LED counter and have
> breadboarded the 6x4094 serial-to-parallel chips.  All seems working
> fine except I have exceeded the current sinking capacity of the 4094s.

 The chip you want may be available, called an "HC4094".  The 74HC164
is a non-latched equivalent while the 74HC595 as you have mentioned,
*is* latched *and* has a "clear" (on the shifter at least, not the
buffer).  If you're using a microcontroller, the need for inversion is
inconsequential.

 Have you not been watching the discussion on "loads of flashing LEDs"?
I was detailing a method of multiplexing LEDs, particularly 7-segment
common-anode displays with one line more than the number of segments,
i.e. you could use eight lines if you didn't want the DPs.

 The obvious implication of this was that you can do the job with a
common-collector transistor array (or SMD transistors) if you can afford
8 or nine pins.  If not, I suppose you would regard a second PIC as too
expensive...

--
 Cheers,
       Paul B.

1998\07\25@132658 by Peter L. Peres

picon face
On Sat, 25 Jul 1998, bill bass wrote:

> Hi, all,
>
> Being new to PIC and interfacing, I have a question for
> PIC members.  Please help.
>
> I am making a 6-digit 7-segment (common anode)LED counter and have
> breadboarded the 6x4094 serial-to-parallel chips.  All seems working
> fine except I have exceeded the current sinking capacity of the 4094s.
>
> I am looking for alternatives to replace the 4094s.  The 74HC595 looks
> like it can source and as well as sink 8mA current comfortably.  That
> means I can use either common anode or common cathode displays at
> will.  Personnally, I like to use positive logic where I don't have to
> complement the output byte.
>
> Can somebody please comment on this approach?  Is there a better way
> of doing other than what I have said?

It should work but if the 4094s are not enough then maybe you should look
into specialized drivers for LEDs. The 4094s are excellent in low power
equipment, exactly where one would use a low current display or LCD to
save power... And I feel guilty because I did not mention that.

If the design is large and static then you might want to look into ULN2803
drivers added to what you have (4094 or 595) which can run a 'Jumbo'
display and even an incandescent filament display at 50 mA / segment. It's
8 * 0.4 A per package or so.

hope this helps,

       Peter

1998\07\25@153621 by Dwayne Reid

flavicon
face
>Being new to PIC and interfacing, I have a question for
>PIC members.  Please help.
>
>I am making a 6-digit 7-segment (common anode)LED counter and have
>breadboarded the 6x4094 serial-to-parallel chips.  All seems working
>fine except I have exceeded the current sinking capacity of the 4094s.
>
>I am looking for alternatives to replace the 4094s.  The 74HC595 looks
>like it can source and as well as sink 8mA current comfortably.  That
>means I can use either common anode or common cathode displays at
>will.  Personnally, I like to use positive logic where I don't have to
>complement the output byte.

The 74CH595 is ideal for this.  Sinking gives lower losses, plus you can
feed your LEDs from a different supply.  If you need lots of current, look
at the TPIC6B595 from TI.  150 mA sinking per output X 8 outputs.  Not pin
compatible with the hc595 though.

I use both parts for driving LEDs, the TI part will also drive lamps.  The
hc595 is my preferred part - I use it only in sinking mode when driving
LEDs.  The reason is that I drive the LEDs from either my unregulated
battery supply (I use PWM to keep the brightness constant as the battery
decays) or from a seperate 4V switch mode supply (line powered industrial
control panel with many LEDs).

As far as the logic level is concerned, don't complement the byte if you
don't have to.  Either modify your lookup table or swap the bsf/bcf
instructions that control the data line in the serial routine.

dwayne


Dwayne Reid   <.....dwaynerKILLspamspam.....planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

1998\07\25@191524 by Chuck Hellebuyck

picon face
> >Being new to PIC and interfacing, I have a question for
> >PIC members.  Please help.
> >
> >I am making a 6-digit 7-segment (common anode)LED counter and have
> >breadboarded the 6x4094 serial-to-parallel chips.  All seems working
> >fine except I have exceeded the current sinking capacity of the 4094s.
> >
> >I am looking for alternatives to replace the 4094s.  The 74HC595 looks
> >like it can source and as well as sink 8mA current comfortably.  That
> >means I can use either common anode or common cathode displays at
> >will.  Personnally, I like to use positive logic where I don't have to
> >complement the output byte.
>

I'm new to the list so maybe this was mentioned.
Try the Maxim MAX7219 Serial LED Display Driver Chip. It will drive up
to eight 7-segment LEDs in a multiplex drive. The PIC interfaces by just three

pins; Serial Data, Load and Clock. You can even get a free sample from MAXIM.
They are at http://www.maxim-ic.com.
--
Chuck Hellebuyck
Electronic Products
Check Out our Serial Large Character LCD Module!
EraseMEeproductsspam_OUTspamTakeThisOuTjuno.com (sorry no attachments)
eproductsspamspam_OUTsprynet.com (for attachments only)
http://www.elproducts.com

1998\07\25@211703 by bill bass

picon face
Hello, Chuck,

Thanks very much for your info.  Yes, indeed the Max-7219 is a good
choice.  I just looked it up and all it takes is 3 PIC I/O lines for a
full 8 digit control - wonderful!!

I then turn to the DigitKey and discovered that the price is $8.27 for
single piece and $4.68 for 100 quantities.  That's too much for a
general purpose application.  You know, this has been a question for
all designers, we have to use the cheapest approach in order to keep
the price on the final product marketable.  Sorry I did not mention
that it is for a product design, not for a one off fun project.

So, back to square one.  Should I use the 74HC595s for around $.4 per
piece to do the job???  The portB on our 16F84 has connected to a
16-key pad which makes multiplexing the display, using portB,  a
problem if one of the key is being pressed solid.

Again, I appreciate your time.


Bill, @spam@Bass_82KILLspamspamYahoo.com



>
> > >Being new to PIC and interfacing, I have a question for
> > >PIC members.  Please help.
> > >
> > >I am making a 6-digit 7-segment (common anode)LED counter and have
> > >breadboarded the 6x4094 serial-to-parallel chips.  All seems
working
> > >fine except I have exceeded the current sinking capacity of the
4094s.
> > >
> > >I am looking for alternatives to replace the 4094s.  The 74HC595
looks
> > >like it can source and as well as sink 8mA current comfortably.
That
> > >means I can use either common anode or common cathode displays at
> > >will.  Personnally, I like to use positive logic where I don't
have to
> > >complement the output byte.
> >
>
> I'm new to the list so maybe this was mentioned.
> Try the Maxim MAX7219 Serial LED Display Driver Chip. It will drive up
> to eight 7-segment LEDs in a multiplex drive. The PIC interfaces by
just three
>
> pins; Serial Data, Load and Clock. You can even get a free sample
from MAXIM.
> They are at http://www.maxim-ic.com.
> --
> Chuck Hellebuyck
> Electronic Products
> Check Out our Serial Large Character LCD Module!
> KILLspameproductsKILLspamspamjuno.com (sorry no attachments)
> RemoveMEeproductsTakeThisOuTspamsprynet.com (for attachments only)
> http://www.elproducts.com
>

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1998\07\25@214612 by bill bass

picon face
Dwayne,

Hi!  Thanks a lot for your information, I really find it useful.

Looks like 5 to 8 mA is all that it takes to drive each segment
reasonably. I will take your advice to drive the segments thru an
unregulated supply so that I can use a 78L05 regulator which further
reduces cost. The HC595 is fine, particularly if  price is a concern.

Thanks again for your help.


Bill, spamBeGonebass_82spamBeGonespamYahoo.com




>
> >Being new to PIC and interfacing, I have a question for
> >PIC members.  Please help.
> >
> >I am making a 6-digit 7-segment (common anode)LED counter and have
> >breadboarded the 6x4094 serial-to-parallel chips.  All seems working
> >fine except I have exceeded the current sinking capacity of the
4094s.
> >
> >I am looking for alternatives to replace the 4094s.  The 74HC595
looks
> >like it can source and as well as sink 8mA current comfortably.  That
> >means I can use either common anode or common cathode displays at
> >will.  Personnally, I like to use positive logic where I don't have
to
> >complement the output byte.
>
> The 74CH595 is ideal for this.  Sinking gives lower losses, plus you
can
> feed your LEDs from a different supply.  If you need lots of
current, look
> at the TPIC6B595 from TI.  150 mA sinking per output X 8 outputs.
Not pin
> compatible with the hc595 though.
>
> I use both parts for driving LEDs, the TI part will also drive
lamps.  The
> hc595 is my preferred part - I use it only in sinking mode when
driving
> LEDs.  The reason is that I drive the LEDs from either my unregulated
> battery supply (I use PWM to keep the brightness constant as the
battery
> decays) or from a seperate 4V switch mode supply (line powered
industrial
> control panel with many LEDs).
>
> As far as the logic level is concerned, don't complement the byte if
you
{Quote hidden}

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1998\07\26@192529 by Dwayne Reid

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face
>Looks like 5 to 8 mA is all that it takes to drive each segment
>reasonably. I will take your advice to drive the segments thru an
>unregulated supply so that I can use a 78L05 regulator which further
>reduces cost. The HC595 is fine, particularly if  price is a concern.

Hi there Bill.

Two things to keep in mind:  you can daisy chain the hc595 chips so that you
need only 1 data line (plus the clock snd strobe).  You can further reduce
the pin count by 1 line if you use a small diode/resistor/capacitor network
as shown in by the sketch below - the downside of this is that the time
delay for the latch must be substantially longer than the clock period.
This may or may not be a concern.

One final note: when I mention driving the anodes of the LEDs directly from
the battery supply, you MUST ensure that the unregulated supply is no more
than about 1.5 Vdc higher than the 5V supply.  This implies 2 possible
situations: use a 6V supply (4x 1.5v) with a low dropout regulator *or* use
a lower voltage battery with a boost convertor.  I have used both techniques
but my preferred is 3x 1.5v for an unregulated supply that varies between
2.5v to 4.8v; with a LT1300 boost regulator to give me the 5V for the
circuit.  Works well and reasonably low cost (at least as far as industrial
users are concerned).  If I were designing for consumers, I would probably
opt for the 6V and LDO choice: cheaper to produce even though you don't get
all the energy possible out of the batteries.

Here is the simple 2 wire interface for hc595 shift registers:

  ------------------------  data

  ------------------------  clock
       |   |
       |   |
       R  --- cathode
       R  /\  in4148
       R  --  anode
       |   |
       |   |
       -------------------- latch
       |
       | +
      ---  chose RC time constant to be about 5X the clock period
      ---
       |
       |
       GND

Shift data out as normal.  On the last rising clock edge, hold clock HI for
about 10X the clock period.  Then bring clock LO and start over again.


dwayne


Dwayne Reid   <RemoveMEdwaynerspamTakeThisOuTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

1998\07\27@134718 by Dr. Imre Bartfai

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face
Hi,
I use 74164's, and they do the job.
Imre


On Sat, 25 Jul 1998, bill bass wrote:

{Quote hidden}

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