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'[EE]: 74LS164'
2001\05\23@003922 by Edson Brusque

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Hello,

   I'm wanting to use three 74LS164 to turn on/off 24 leds.

   Is it possible to use just two PIC outputs to control various cascaded
74LS164? I mean, wiring the Output7 from the first to the DATA input of the
second and so on. Any experiences about this?

   Thanks,

   Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2138  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
http://www.citronics.com.br
-----------------------------------

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2001\05\23@011247 by David W. Gulley

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Edson Brusque wrote:
>     I'm wanting to use three 74LS164 to turn on/off 24 leds.
>
>     Is it possible to use just two PIC outputs to control various cascaded
> 74LS164? I mean, wiring the Output7 from the first to the DATA input of the
> second and so on. Any experiences about this?

I have used a similar approach where the QH of one device was connected
to both the A and B inputs of the next device. The outputs were
connected to LEDs such that a LOW on the output would light the LED
(since the devices cannot source much current). The LEDs were updated by
shifting bits into the register quickly.

This scheme worked very well, using only a data and a clock to drive the
shift registers.

Make sure you take into consideration the current requirements of the
LEDs when selecting devices, since the 74LS164 has a max recommended IOL
of 8mA.

David W. Gulley
Destiny Designs

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2001\05\23@022558 by Russell McMahon

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> >     Is it possible to use just two PIC outputs to control various
cascaded
> > 74LS164? I mean, wiring the Output7 from the first to the DATA input of
the
> > second and so on. Any experiences about this?

> Make sure you take into consideration the current requirements of the
> LEDs when selecting devices, since the 74LS164 has a max recommended IOL
> of 8mA.

I have checked for the 74xx164 parts but in most cases the 74HC and 74HCT
parts have very similar Iout low current specs and much lower quiescent
current specs (typically under 1 mA compared to about 20+ mA for the LS
part). The prices are generally about the same or cheaper than LS.

LS was a fine logic family in its day but it's day has gone. Using a CMOs
equivalent is preferable unless there is a very good reason to use LS (like
perhaps having a drawerful of them? :-) ).



Russell McMahon

. .

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2001\05\23@035121 by Jinx

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>     I'm wanting to use three 74LS164 to turn on/off 24 leds.
>
>     Is it possible to use just two PIC outputs to control various cascaded
> 74LS164? I mean, wiring the Output7 from the first to the DATA input
> of the second and so on. Any experiences about this?

The 164 advances on the L-H clock transition. Depending on the app
and data you may need to invert the signal from q7 and the CP of the
next 164

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2001\05\23@035752 by Alexandre Domingos F. Souza

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>>     I'm wanting to use three 74LS164 to turn on/off 24 leds.
>>     Is it possible to use just two PIC outputs to control various cascaded
>> 74LS164? I mean, wiring the Output7 from the first to the DATA input
>> of the second and so on. Any experiences about this?
>The 164 advances on the L-H clock transition. Depending on the app
>and data you may need to invert the signal from q7 and the CP of the
>next 164

       Better use the good old 4017, 10 outputs and just a clock input. :o)

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2001\05\23@040154 by Jinx

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> The 164 advances on the L-H clock transition. Depending on the app
> and data you may need to invert the signal from q7 and the CP of the
> next 164

My mistake - I'm working on a 12-digit driver using 4017s/ULN2003s
and got carried away. ISTR that this was asked some time ago. You'd
connect CPs together and MRs together and q7 -> Data. But I also
recall that someone tried this and lost data bits, don't remember why

I recently made this display

http://home.clear.net.nz/pages/joecolquitt/2wireled.html

on which I found it was not necessary to explicitly use the 164's MR

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2001\05\23@041307 by Ray Gardiner

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I don't see why that would not work for LED's, but I
think you should look for something with latched
outputs, like the 74HC595 or similiar, that way you won't
get glitches when updating the outputs. However an extra
line is required to strobe the latches. Past experience has
shown that you usually can combine this with some other
function, so it doesn't cost you an extra pin after all :-)



{Quote hidden}

Ray Gardiner spam_OUTrayTakeThisOuTspamdsp.com.au
[ 2001 ]

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2001\05\23@071346 by Bob Ammerman

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> Hello,
>
>     I'm wanting to use three 74LS164 to turn on/off 24 leds.
>
>     Is it possible to use just two PIC outputs to control various cascaded
> 74LS164? I mean, wiring the Output7 from the first to the DATA input of
the
> second and so on. Any experiences about this?
>
>     Thanks,
>
>     Brusque

This will work fine, with one possible problem:

The Q7 output of each '164 is driving not only an LED but also the next
'164.

Depending on the LED current, the Vol of this output may rise too high to
give you a good noise margin into the next '164.

Of course, your LEDs will be connected, via a resistor from +5V to the
outputs of the '164.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\05\23@072232 by Bob Ammerman
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> I don't see why that would not work for LED's, but I
> think you should look for something with latched
> outputs, like the 74HC595 or similiar, that way you won't
> get glitches when updating the outputs. However an extra
> line is required to strobe the latches. Past experience has
> shown that you usually can combine this with some other
> function, so it doesn't cost you an extra pin after all :-)

Depending on the update rate of the LEDs you will _not_ see any glitching.
The '164 will do the job just fine.

(But the '595 is a nice chip).

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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