connecting TTL o/p together

  • Thread starter fynnashba@yahoo.com
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fynnashba@yahoo.com

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Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks
 
fynnashba@yahoo.com wrote:
Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks
If you take 8 small switching PNP transistors and join all the Emitters
Click to expand...
and collectors together, you can create a 8 input OR gate. the collector
cluster can connect to one R to common to provide a low side signal on
the output. Each Base of each transistor can be driven with a 10k R from
a TTL level signal, this will provide you 8 inputs. The Emitter cluster
connects to your 5V+ supply..


The output will be at your Collector cluster..
 
fynnashba@yahoo.com wrote:

Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks
I made an error with the last post.
Click to expand...

Make the same circuit but use NPN instead of PNP's and just do the
reverse of what I posted before.

Emitter cluster to common, Collector cluster to a Load R from the
5 Volt supply.. 10k driving each NPN for your 8 inputs.
On the Load R, have that go to a NPN stage to invert the output, other
wise, you have a Nor gate instead..
 
"fynnashba@yahoo.com" <fynnashba@yahoo.com> writes:

Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks
Click to expand...
Nope. :) But you could use a pair of 74LS32s.

Or any of a zillion other ways of combining gates.

Also search for "open collector".

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Important: Anything sent to the email address in the message header above is
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subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
On Fri, 15 Oct 2010 16:21:34 -0700 (PDT), "fynnashba@yahoo.com"
<fynnashba@yahoo.com> wrote:

Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks
Click to expand...
Devices that have "open collector" outputs can, generally, be tied
together. Normal TTL outputs, however, are active (see
<http://en.wikipedia.org/wiki/Transistor–transistor_logic#TTL_with_a_.22totem-pole.22_output_stage>)
and should not be tied together in this manner.

You can get the results you are looking for just by using a second
74LS32. Take the four outputs of the first one to two gates (four
inputs) on the second. Take the resulting two outputs to one of the
remaining OR gates and you're done, modulo the cumulative effects of the
gate delays.

A "real" 8-to-1 OR-gate could be realized in a small programmable logic
device. A GAL could do this easily but programming one could be a
challenge if you don't have access to a proper device programmer.

I'd go with the two 74LS32s.

--
Rich Webb Norfolk, VA
 
Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks
Click to expand...
No. Connect pairs of dual OR-gate outputs to two dual OR-gates, then those
to a single OR gate. What could be simpler?
 
In article <i9at5o$stl$1@news.eternal-september.org>,
grizzledgeezer@comcast.net says...
Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks

No. Connect pairs of dual OR-gate outputs to two dual OR-gates, then those
to a single OR gate. What could be simpler?
Click to expand...
How about 4 diodes and a resistor?
__
-\ \
| |-->|-|
-/__/ |
__ |
-\ \ |
| |-->|-|
-/__/ |
__ |
-\ \ |
| |-->|-+----- out
-/__/ |
__ |
-\ \ |
| |-->|-|
-/__/ |
|
.-.
| | 10k
| |
'-'
|
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-
chat.de)
 
In article <79559909-a5f3-4eae-a99d-
1027f71af88c@t20g2000yqa.googlegroups.com>,
rosemontcrest@yahoo.com says...

[snip]

How about simply 8 diodes and 1 resistor with no gates? Depending on
the load connected to the output, the resistor may not be necessary.
Click to expand...
Very true. The OP said he was using 7432's, but
he could get by without them...
 
On Oct 15, 7:18 pm, Randy Day <randy....@sasktel.netx> wrote:
In article <i9at5o$st...@news.eternal-september.org>,
grizzledgee...@comcast.net says...

 Hi l'm building a circuit and l need  an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks

No. Connect pairs of dual OR-gate outputs to two dual OR-gates, then those
to a single OR gate. What could be simpler?

How about 4 diodes and a resistor?
         __
       -\  \
         |  |-->|-|
       -/__/      |
         __       |
       -\  \      |
         |  |-->|-|
       -/__/      |
         __       |
       -\  \      |
         |  |-->|-+----- out
       -/__/      |
         __       |
       -\  \      |
         |  |-->|-|
       -/__/      |
                  |
                 .-.
                 | | 10k
                 | |
                 '-'
                  |
                  |
                 ==>                  GND
(created by AACircuit v1.28.6 beta 04/19/05www.tech-
chat.de)
Click to expand...
How about simply 8 diodes and 1 resistor with no gates? Depending on
the load connected to the output, the resistor may not be necessary.
 
On Oct 15, 9:23 pm, Randy Day <randy....@sasktel.netx> wrote:
In article <79559909-a5f3-4eae-a99d-
1027f71af...@t20g2000yqa.googlegroups.com>,
rosemontcr...@yahoo.com says...

[snip]

How about simply 8 diodes and 1 resistor with no gates? Depending on
the load connected to the output, the resistor may not be necessary.

Very true. The OP said he was using 7432's, but
he could get by without them...
Click to expand...
Some advantages of the diode-only approach may include:

1) It's inexpensive
2) It's easily expanded if another input is desired
3) Small-signal diodes rarely fail, so it's likely to be very reliable
4) Assuming through-hole technology, it can occupy about the same
space as one 16-pin DIP
5) If PCB real estate is limited, leaded-diodes can be incorporated
into wiring harnesses
 
fynnashba@yahoo.com wrote:
Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks
Click to expand...
Presumably you (only) need LS speed?

The clumsy way to do this is to feed two signals to each of four gates.
This consumes a DIP14.

Take the outputs from the four gates and run them, in pairs, to the
inputs of two more '32 gates (half of a second DIP14).

Finally, connect the outputs of these two gates to a third gate
in that second package.

32's are slow so this approach is *very* slow.

Another approach is to replace the quad OR with a quad *NOR*.
This uses a DIP14.

Feed these four outputs into a quad *NAND* -- the output of
which will be your desired logic function. Should be faster
end-to-end at the expense of having to use two different
devices.

Another approach is to pass the signals through open collector
inverters. Six per DIP14 so you will need 1 and a third packages.

Tie *all* of the outputs together -- and two a pullup resistor.
Finally, pass this signal through one of the remaining inverters
being sure to add a pullup on its output, as well.

Other variations are possible: e.g., a pair of quad NORs feeding
a dual NAND; three triple NORs feeding a triple NAND; etc.

Usually, one checks to see what "spare gates" one has available
elsewhere in the circuit in order to select the most opportune
implementation.
 
Randy Day wrote:
In article <i9at5o$stl$1@news.eternal-september.org>,
grizzledgeezer@comcast.net says...
Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks

No. Connect pairs of dual OR-gate outputs to two dual OR-gates, then those
to a single OR gate. What could be simpler?

How about 4 diodes and a resistor?
__
-\ \
| |-->|-|
-/__/ |
__ |
-\ \ |
| |-->|-|
-/__/ |
__ |
-\ \ |
| |-->|-+----- out
-/__/ |
__ |
-\ \ |
| |-->|-|
-/__/ |
|
.-.
| | 10k
| |
'-'
|
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-
chat.de)
Click to expand...

There are good reasons why Diode Logic & DTL died in the '60s.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
 
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:FrWdnRc_SJYx7iTRnZ2dnUVZ_tSdnZ2d@earthlink.com...
Randy Day wrote:

In article <i9at5o$stl$1@news.eternal-september.org>,
grizzledgeezer@comcast.net says...
Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together
as
one just like that? thanks

No. Connect pairs of dual OR-gate outputs to two dual OR-gates, then
those
to a single OR gate. What could be simpler?

How about 4 diodes and a resistor?
__
-\ \
| |-->|-|
-/__/ |
__ |
-\ \ |
| |-->|-|
-/__/ |
__ |
-\ \ |
| |-->|-+----- out
-/__/ |
__ |
-\ \ |
| |-->|-|
-/__/ |
|
.-.
| | 10k
| |
'-'
|
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-
chat.de)


There are good reasons why Diode Logic & DTL died in the '60s.
Click to expand...
That is true Michael, but depending on the exact application, implementing
an OR function with diodes can still be the simplest way to get a 'wide'
array I tend to use schottky types these days for the speed and lower
forward voltage drop. Otherwise, as others have said in the thread either
use two common TTL gates, or better yet, just use a CMOS 4078. This device
will work happily at TTL supply and drive levels and is an 8 i/p OR function
in a single 14 pin package.

Arfa
 
Arfa Daily wrote:
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:FrWdnRc_SJYx7iTRnZ2dnUVZ_tSdnZ2d@earthlink.com...

Randy Day wrote:

In article <i9at5o$stl$1@news.eternal-september.org>,
grizzledgeezer@comcast.net says...
Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together
as
one just like that? thanks

No. Connect pairs of dual OR-gate outputs to two dual OR-gates, then
those
to a single OR gate. What could be simpler?

How about 4 diodes and a resistor?
__
-\ \
| |-->|-|
-/__/ |
__ |
-\ \ |
| |-->|-|
-/__/ |
__ |
-\ \ |
| |-->|-+----- out
-/__/ |
__ |
-\ \ |
| |-->|-|
-/__/ |
|
.-.
| | 10k
| |
'-'
|
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-
chat.de)


There are good reasons why Diode Logic & DTL died in the '60s.



That is true Michael, but depending on the exact application, implementing
an OR function with diodes can still be the simplest way to get a 'wide'
array I tend to use schottky types these days for the speed and lower
forward voltage drop. Otherwise, as others have said in the thread either
use two common TTL gates, or better yet, just use a CMOS 4078. This device
will work happily at TTL supply and drive levels and is an 8 i/p OR function
in a single 14 pin package.
Click to expand...

The disadvantages are slow speeds and higher operating currents.
Both can cause problems in some designs. If it is a very slow device,
and has no power restraints it is acceptable.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
 
On Oct 16, 2:09 am, D Yuniskis <not.going.to...@seen.com> wrote:
fynnas...@yahoo.com wrote:
 Hi l'm building a circuit and l need  an 8 input OR gate
Click to expand...
[start with a bundle of 2-in NOR gates]
Feed these four outputs into a quad *NAND* -- the output of
which will be your desired logic function.  Should be faster
end-to-end at the expense of having to use two different
devices.
Click to expand...
Just to expand on this a bit...
The basic one-stage TTL circuit can do AND/OR/INVERT, so
NAND and NOR and INVERT are all one-stage logic functions.
AND, OR, and BUFFER(noninverting) gates all have to have
two stages, so are all slower.

It's different for CMOS logic.
 
On Fri, 15 Oct 2010 16:21:34 -0700 (PDT) "fynnashba@yahoo.com"
<fynnashba@yahoo.com> wrote in Message id:
<4abefe43-8a42-4a8b-b92a-e4e5340f9fce@g8g2000yqa.googlegroups.com>:

Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks
Click to expand...
How about an STM 74HC4078? Mouser has stock. Part #511-M74HC4078.
 
Gus wrote:
On Oct 15, 6:21 pm, "fynnas...@yahoo.com" <fynnas...@yahoo.com> wrote:
Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks

54/74 4078

https://www.distrelec.com/distrelec/datasheets.nsf/WebAttachments/794F633EBC2064D3C12570EA0003E06B/$File/647838.pdf
You can only wire together open collector outputs.
Click to expand...
74xx05, 6 invertors with open collector output, wire the
outputs together.
For two chips, using one invertor to make the 11 input nor
into an 11 input or, needing two pull up resistors.
 
On Oct 15, 6:21 pm, "fynnas...@yahoo.com" <fynnas...@yahoo.com> wrote:
 Hi l'm building a circuit and l need  an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks
Click to expand...
54/74 4078

https://www.distrelec.com/distrelec/datasheets.nsf/WebAttachments/794F633EBC2064D3C12570EA0003E06B/$File/647838.pdf
 
"JW" <none@dev.null> wrote in message
news:u36ob6973lh5777esr61p3re7g3lmj34i4@4ax.com...
On Fri, 15 Oct 2010 16:21:34 -0700 (PDT) "fynnashba@yahoo.com"
fynnashba@yahoo.com> wrote in Message id:
4abefe43-8a42-4a8b-b92a-e4e5340f9fce@g8g2000yqa.googlegroups.com>:


Hi l'm building a circuit and l need an 8 input OR gate(does anyone
know of one ?) this is not available so l'm using 74LS32 - Dual input
Quad or gate. the problem is can l connect all the outputs together as
one just like that? thanks

How about an STM 74HC4078? Mouser has stock. Part #511-M74HC4078.
Click to expand...
I already suggested that a coupla days back ... :)

Arfa
 
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