multiplexer question

[panfilero]

Hello, I was wondering if there is such a thing as a 16 to 1
multiplexer. I need something that can connect 16 individual inputs to
1 output 1 at a time in sequence. But I'm having trouble finding a
16:1 MUX. Also, I ordered some chips from mouser, and some are big
enough to stick in my bredboard but a lot of them were real tiny...
does anyone know what's up with the real tiny ones? I couldn't find in
the name of the chip something that would let me know that it was going
to be too tiny to fit in a regular solderless breadboard.

thanks

 

[Eric Smith]

"panfilero" <panfilero@gmail.com> writes:

Hello, I was wondering if there is such a thing as a 16 to 1
multiplexer. I need something that can connect 16 individual inputs to
1 output 1 at a time in sequence. But I'm having trouble finding a
16:1 MUX.

The normal approach is to use two 8:1 three-state multiplexers
(e.g., 74xx251) and an inverter (e.g., 74xx04).

For 16 inputs, you need four bits to select a particular input.
Tie three of those bits to the select lines of both mutliplexers.
The the fourth selection signal to the output enable of one
multiplexer, and the complement of that signal (formed by an inverter)
to the output enable of the other multiplexer.

For a 5V system, unless you are dealing with very fast signals (e.g.,
faster than 20 MHz), the most common choices for the family would be
LS or HCT, or if you are using only CMOS logic (no bipolar), HC.

Also, I ordered some chips from mouser, and some are big
enough to stick in my bredboard but a lot of them were real tiny...
does anyone know what's up with the real tiny ones?

Those are surface-mount parts, typically in SO, SSOP, or TSSOP
packages. Make sure you order DIP package parts instead. Note
that many newer chips aren't available in DIP, but 74LS, 74HCT,
and 74HC generally are.

The vendors have various suffixes to designate packages. For TI,
the "N" suffix is for DIP packages, vs. "D" or "DW" for SO, etc.
If you're not sure, the Mouser catalog or web site should indicate which
package a part is in, so you can check before you order.

Eric

 

[Steve]

In article <qhodpfu9n0.fsf@ruckus.brouhaha.com>, eric@brouhaha.com (Eric
Smith) wrote:

*Subject:* Re: multiplexer question
*From:* Eric Smith <eric@brouhaha.com
*Date:* 03 Jan 2007 12:40:19 -0800

"panfilero" <panfilero@gmail.com> writes:
Hello, I was wondering if there is such a thing as a 16 to 1
multiplexer. I need something that can connect 16 individual
inputs to
1 output 1 at a time in sequence. But I'm having trouble finding
a
16:1 MUX.

The normal approach is to use two 8:1 three-state multiplexers
(e.g., 74xx251) and an inverter (e.g., 74xx04).

For 16 inputs, you need four bits to select a particular input.
Tie three of those bits to the select lines of both mutliplexers.
The the fourth selection signal to the output enable of one
multiplexer, and the complement of that signal (formed by an
inverter)
to the output enable of the other multiplexer.

Or use a 4067 ? Available in 0.6" DIP I use them often. 4 bit, 1>16 or
16>1 with OE.

http://focus.ti.com/lit/ds/symlink/cd4067b.pdf

or latched...

http://www.datasheetcatalog.com/datasheets_pdf/C/D/4/5/CD4514.shtml



- Steve