Best way to ensure signal does not exceed 5v?

On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb

of 5v. I have NO IDEA how to do this and was hoping someone here
could suggest a simple solution to cap a signal at a max of 5v.

Thanks, John, but this is much cheaper:

DAQ
. +-------+
. | OUT|--[4.7K]--+-->To logic
. +-------+ |
. [1N4148]
. | K
. |
. +5V

On Fri, 02 Sep 2011 09:32:59 -0500, "krw_at_att.bizzzzzzzzzzzz"
krw_at_att.bizzzzzzzzzzzz> wrote:

On Fri, 02 Sep 2011 08:49:22 -0500, John Fields
jfields_at_austininstruments.com> wrote:

On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb
steveklett_at_gmail.com> wrote:

I'm the "software guy" but am trying to help out on the hardware side
for a small project we have going on. It's fun, I like to learn new
stuff. I'm currently working on a circuit that is connected to a
piece of data acquisition hardware that provides 8 digital bits (1
port) and these 8 bits are wired up to a set of decoder ICs. Great,
that all works fine. The problem is that I need ONE MORE digital bit
to control a SSR - but I don't have any more available digital pins so
I'm going to use one of the analog outputs on the DAQ hardware.

OK, finally my question: The analog out can be software controlled to
output 0 - 10v. If I connect this straight to a logic pins this means
that if someone screws up (people always do) they could fry things by
accidentally sending 10v to a part that is expecting a maximum of 5v.
I would like to add a little circuitry to cap the analog line at a max
of 5v. I have NO IDEA how to do this and was hoping someone here
could suggest a simple solution to cap a signal at a max of 5v.

---
View with a fixed-pitch font:

DAQ
. +-------+
. | OUT|--[4.7K]--+-->To logic
. +-------+ |
. [LM386-5.0]
. |
. GND

http://www.national.com/ds/LM/LM136-5.0.pdf


Oh, that's good. A $6 solution where a $.004 solution is better and
smaller.

---
Mea Culpa.

Actually less than a US dollar, but what have you got that's less than
half a penny?

The best price I got at Digi-Key is .006 for a 1N4148.

Rich Grise wrote:
John Fields wrote:

On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb


of 5v. I have NO IDEA how to do this and was hoping someone here
could suggest a simple solution to cap a signal at a max of 5v.

Thanks, John, but this is much cheaper:

DAQ
. +-------+
. | OUT|--[4.7K]--+-->To logic
. +-------+ |
. [1N4148]
. | K
. |
. +5V


And I'd probably have used a 1K, depending on the output
drive of the DAQ.

Cheers!
Rich

ok lets see, and the +5 is coming from where? Does it have
the ability to sink anything coming back to it, like a zener clamp?

I'd had to see that +5 source being supplied from a 7805/78L04 regs or
like them. Love the effects of over voltage on other items attached to
that circuit!

John Fields wrote:

On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb


of 5v. I have NO IDEA how to do this and was hoping someone here
could suggest a simple solution to cap a signal at a max of 5v.

Thanks, John, but this is much cheaper:

DAQ
. +-------+
. | OUT|--[4.7K]--+-->To logic
. +-------+ |
. [1N4148]
. | K
. |
. +5V


And I'd probably have used a 1K, depending on the output
drive of the DAQ.

Cheers!
Rich

ok lets see, and the +5 is coming from where? Does it have

"SklettTheNewb"

Lots of info here, this thing has taken on a life of it's own. After
re-evaluating my requirements against my knowledge/abilities and time
constraints I have selected the voltage divider solution:
#1 my primary goal was to avoid hardware damage - check!
#2 If myself and my team can't read code comments and follow
instructions to output 10v then I have bigger issues to worry about.


** The KISS principle applies here.

There are virtually no reasons not to use a simple divider.

You also give Mr Murphy a wide berth too by using a passive solution.



.... Phil

I'm the "software guy" but am trying to help out on the hardware side
for a small project we have going on. It's fun, I like to learn new
stuff. I'm currently working on a circuit that is connected to a
piece of data acquisition hardware that provides 8 digital bits (1
port) and these 8 bits are wired up to a set of decoder ICs. Great,
that all works fine. The problem is that I need ONE MORE digital bit
to control a SSR - but I don't have any more available digital pins so
I'm going to use one of the analog outputs on the DAQ hardware.

OK, finally my question: The analog out can be software controlled to
output 0 - 10v. If I connect this straight to a logic pins this means
that if someone screws up (people always do) they could fry things by
accidentally sending 10v to a part that is expecting a maximum of 5v.
I would like to add a little circuitry to cap the analog line at a max
of 5v. I have NO IDEA how to do this and was hoping someone here
could suggest a simple solution to cap a signal at a max of 5v.

Thanks for reading!

-Steve
use one bit to enable/disable two 7 bit registers, that gives

Rich Grise wrote:
John Fields wrote:
On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb

of 5v. I have NO IDEA how to do this and was hoping someone here
could suggest a simple solution to cap a signal at a max of 5v.

Thanks, John, but this is much cheaper:

DAQ
. +-------+
. | OUT|--[4.7K]--+-->To logic
. +-------+ |
. [1N4148]
. | K
. |
. +5V

And I'd probably have used a 1K, depending on the output
drive of the DAQ.

ok lets see, and the +5 is coming from where? Does it have
the ability to sink anything coming back to it, like a zener clamp?

I'd had to see that +5 source being supplied from a 7805/78L04 regs or
like them. Love the effects of over voltage on other items attached to
that circuit! :)

Do pay no attention to me, I just happen to be very observative.

Did you mean "observant?"

Jamie wrote:

Rich Grise wrote:

John Fields wrote:

On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb

of 5v. I have NO IDEA how to do this and was hoping someone here
could suggest a simple solution to cap a signal at a max of 5v.

Thanks, John, but this is much cheaper:

DAQ
. +-------+
. | OUT|--[4.7K]--+-->To logic
. +-------+ |
. [1N4148]
. | K
. |
. +5V

And I'd probably have used a 1K, depending on the output
drive of the DAQ.


ok lets see, and the +5 is coming from where? Does it have
the ability to sink anything coming back to it, like a zener clamp?

I'd had to see that +5 source being supplied from a 7805/78L04 regs or
like them. Love the effects of over voltage on other items attached to
that circuit! :)

Do pay no attention to me, I just happen to be very observative.


Did you mean "observant?"
Nope, that is exactly what I meant to say, you must remember that I was

But to answer your question, the source of the +5V is left as an exercise
for the student. ;-)

Cheers!
Rich