Best way to ensure signal does not exceed 5v?

S

SklettTheNewb

Guest
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
 
"SklettTheNewb"
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.
Click to expand...
** OK,

make the analog output 10 volts and then reduce this to 5 with two equal
value resistors in series.

The mid point voltage will be half the value across the pair.

Aka - a voltage divider.

Two 2.2 kohm resistors might be about right.


...... Phil
 
On Sep 2, 12:17 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"SklettTheNewb"











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.

 **  OK,

 make the analog output 10 volts and then reduce this to 5 with two equal
value resistors in series.

 The mid point voltage will be half the value across the pair.

 Aka  -  a voltage divider.

 Two 2.2 kohm resistors might be about right.

.....  Phil
Click to expand...
Thanks Phil. Although that suggestion would work ( I could also use a
basic voltage regulator, right?) it could result in undefined results
if the user does the RIGHT thing and sets the DAC to 5v. So maybe my
question should be: How can I cap a 5-10v signal to 5v?
 
On Fri, 2 Sep 2011 01:22:32 -0700 (PDT), SklettTheNewb
<steveklett@gmail.com> wrote:

On Sep 2, 12:17=A0am, "Phil Allison" <phi...@tpg.com.au> wrote:
"SklettTheNewb"











I'm the "software guy" but am trying to help out on the hardware side
for a small project we have going on. =A0It's fun, I like to learn new
stuff. =A0I'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. =A0Great,
that all works fine. =A0The 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. =A0If I connect this straight to a logic pins this mean=
s
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. =A0I 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.

=A0** =A0OK,

=A0make the analog output 10 volts and then reduce this to 5 with two equ=
al
value resistors in series.

=A0The mid point voltage will be half the value across the pair.

=A0Aka =A0- =A0a voltage divider.

=A0Two 2.2 kohm resistors might be about right.

..... =A0Phil

Thanks Phil. Although that suggestion would work ( I could also use a
basic voltage regulator, right?) it could result in undefined results
if the user does the RIGHT thing and sets the DAC to 5v. So maybe my
question should be: How can I cap a 5-10v signal to 5v?
Click to expand...
I assume that you have access to the 5V supply used by the
logic you are driving. In that case, the analog output
could drive a series resistor (in the 1-10K range) that
drives the logic gate. From the junction of the resistor
and the logic input, run an ordinary signal diode to +5V.
The "arrow" of the diode should point to +5. Now if the
analog input ever goes above +5, the diode will clamp the
logic side of the resistor to +5.

Note that the resistor is not part of a voltage divider
here. When the analog voltage is below 5V, the current that
flows through the resistor will be low, determined by the
effective input resistance of the logic (which is very high
for CMOS gates). So the resistor will not be dropping any
significant voltage. When the analog output is over 5V, the
current is determined by the difference with +5: At analog
+10, there will be 5V across the resistor. If the resistor
is (say) 10K, then the current delivered by the analog
output will be 5/10K = 0.5 mA, which presumably it can
handle with ease.

Best regards,


Bob Masta

DAQARTA v6.02
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
Science with your sound card!
 
On Fri, 2 Sep 2011 01:22:32 -0700 (PDT), SklettTheNewb
<steveklett@gmail.com> wrote:

On Sep 2, 12:17 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"SklettTheNewb"











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.

 **  OK,

 make the analog output 10 volts and then reduce this to 5 with two equal
value resistors in series.

 The mid point voltage will be half the value across the pair.

 Aka  -  a voltage divider.

 Two 2.2 kohm resistors might be about right.

.....  Phil

Thanks Phil. Although that suggestion would work ( I could also use a
basic voltage regulator, right?) it could result in undefined results
if the user does the RIGHT thing and sets the DAC to 5v. So maybe my
question should be: How can I cap a 5-10v signal to 5v?
Click to expand...
One common way is with a "clamp." Your signal voltage has to have
some series resistance intrinsic to it, or supplied by you, so an over
voltage condition doesn't fry the source of the signal.

Common practice on very high input impedance devices is to just add a
10K in series (that could also be your divider value - so no extra
resistor needed) then you put a clamping diode that shunts any XS
voltage into the + power supply.

Signal voltage goes to 5 volts, nothing happens. Signal tries to
creep over 5 and the diode conducts and limits it to whatever the DAC
supply voltage is (presumably 5+ for this application) - Plus the
voltage drop of the diode.

This scheme is used on plus and minus inputs on op amps and similar
voltage sensitive inputs with diodes to both supply rails. Many PICs
ADCs, Op amps, and the like, already contain built in protection
diodes - in that case, no worries providing your XS voltage is current
limited with a resistor.

OR just put a tested and verified 5.1 volt zener diode to clamp the
input voltage,

In any case, you do need some resistance to limit current. Connecting
a 12 volt car battery to a clamp with no resistance will just fry the
clamping diode then fry the thing you were trying to protect.
 
On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb
<steveklett@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.
Click to expand...
---
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


--
JF
 
On Fri, 02 Sep 2011 08:49:22 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb
steveklett@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
Click to expand...
Oh, that's good. A $6 solution where a $.004 solution is better and smaller.
 
On Sep 2, 4:22 am, SklettTheNewb <stevekl...@gmail.com> wrote:
On Sep 2, 12:17 am, "Phil Allison" <phi...@tpg.com.au> wrote:





"SklettTheNewb"

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.

 **  OK,

 make the analog output 10 volts and then reduce this to 5 with two equal
value resistors in series.

 The mid point voltage will be half the value across the pair.

 Aka  -  a voltage divider.

 Two 2.2 kohm resistors might be about right.

.....  Phil

Thanks Phil.  Although that suggestion would work ( I could also use a
basic voltage regulator, right?)  it could result in undefined results
if the user does the RIGHT thing and sets the DAC to 5v.  So maybe my
question should be: How can I cap a 5-10v signal to 5v?- Hide quoted text -

- Show quoted text -
Click to expand...
Oh you just have to define the 'RIGHT' thing as a ouputing 10V volts
into the voltage divider. The wrong thing is a 5 Volt output, but
now this doens't break anything.

It's hard to beat the two resistor solution.

George H.
 
On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb
<steveklett@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.

Thanks for reading!

-Steve
Click to expand...
A 5.1 volt zener diode to ground should do it. The analog output is
almost surely current limited.

John
 
On Fri, 02 Sep 2011 01:22:32 -0700, SklettTheNewb wrote:

On Sep 2, 12:17 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"SklettTheNewb"











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.

 **  OK,

 make the analog output 10 volts and then reduce this to 5 with two
 equal
value resistors in series.

 The mid point voltage will be half the value across the pair.

 Aka  -  a voltage divider.

 Two 2.2 kohm resistors might be about right.

.....  Phil

Thanks Phil. Although that suggestion would work ( I could also use a
basic voltage regulator, right?) it could result in undefined results
if the user does the RIGHT thing and sets the DAC to 5v. So maybe my
question should be: How can I cap a 5-10v signal to 5v?
Click to expand...
Define the "right" thing as setting the DAC to full range.

Or use a comparator, use a 33k resistor off of the DAC, a 10k to ground,
and an LM339 (powered from 5V) set up with a threshold of 2.5V. Then
you'll always get a clean signal.

But a voltage divider like Phil suggested, plus maybe a yardstick, is
easiest.

(The yardstick is to whack folks upside the head when they feed the wrong
number to the DAC).

--
www.wescottdesign.com
 
On Thu, 01 Sep 2011 22:27:29 -0700, SklettTheNewb 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.
Click to expand...
All the suggestions so far, or a transistor with built-in bias and a
resistor (like this one: http://search.digikey.com/scripts/DkSearch/
dksus.dll?Detail&name=FJY3013RCT-ND). Emitter to ground, base to the DAC,
collector to a 10k resistor to +5V. Take your output off of the
transistor collector. It'll invert, but that's OK -- software is
supposed to fix things like that.

Note that all of the suggestions so far are to some extent kinda slow --
if really snappy action is necessary (and you can somehow get it out of
the DAC), then point this out. Ditto if you have any current
requirements more than a few mA.


--
www.wescottdesign.com
 
On Fri, 02 Sep 2011 12:22:05 -0700, Globemaker wrote:

On Sep 2, 11:59 am, Tim Wescott <t...@seemywebsite.com> wrote:
On Thu, 01 Sep 2011 22:27:29 -0700, SklettTheNewb 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.

All the suggestions so far, or a transistor with built-in bias and a
resistor (like this one:http://search.digikey.com/scripts/DkSearch/
dksus.dll?Detail&name=FJY3013RCT-ND).  Emitter to ground, base to the
DAC, collector to a 10k resistor to +5V.  Take your output off of the
transistor collector.  It'll invert, but that's OK -- software is
supposed to fix things like that.

Note that all of the suggestions so far are to some extent kinda slow
-- if really snappy action is necessary (and you can somehow get it out
of the DAC), then point this out.  Ditto if you have any current
requirements more than a few mA.

--www.wescottdesign.com

a germanium diode clamp to 5v is better than silicon diode clamp.
Click to expand...
Until your production line stalls because you can't find parts.

--
www.wescottdesign.com
 
On Fri, 02 Sep 2011 14:33:08 -0500, Tim Wescott <tim@seemywebsite.com> wrote:

On Fri, 02 Sep 2011 12:22:05 -0700, Globemaker wrote:

On Sep 2, 11:59 am, Tim Wescott <t...@seemywebsite.com> wrote:
On Thu, 01 Sep 2011 22:27:29 -0700, SklettTheNewb 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.

All the suggestions so far, or a transistor with built-in bias and a
resistor (like this one:http://search.digikey.com/scripts/DkSearch/
dksus.dll?Detail&name=FJY3013RCT-ND).  Emitter to ground, base to the
DAC, collector to a 10k resistor to +5V.  Take your output off of the
transistor collector.  It'll invert, but that's OK -- software is
supposed to fix things like that.

Note that all of the suggestions so far are to some extent kinda slow
-- if really snappy action is necessary (and you can somehow get it out
of the DAC), then point this out.  Ditto if you have any current
requirements more than a few mA.

--www.wescottdesign.com

a germanium diode clamp to 5v is better than silicon diode clamp.

Until your production line stalls because you can't find parts.
Click to expand...
Use a Schottky, then.
 
On Sep 2, 11:59 am, Tim Wescott <t...@seemywebsite.com> wrote:
On Thu, 01 Sep 2011 22:27:29 -0700, SklettTheNewb 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.

All the suggestions so far, or a transistor with built-in bias and a
resistor (like this one:http://search.digikey.com/scripts/DkSearch/
dksus.dll?Detail&name=FJY3013RCT-ND).  Emitter to ground, base to the DAC,
collector to a 10k resistor to +5V.  Take your output off of the
transistor collector.  It'll invert, but that's OK -- software is
supposed to fix things like that.

Note that all of the suggestions so far are to some extent kinda slow --
if really snappy action is necessary (and you can somehow get it out of
the DAC), then point this out.  Ditto if you have any current
requirements more than a few mA.

--www.wescottdesign.com
Click to expand...
a germanium diode clamp to 5v is better than silicon diode clamp.
 
On Friday, September 2, 2011 1:22:32 AM UTC-7, SklettTheNewb wrote:

... it could result in undefined results
if the user does the RIGHT thing and sets the DAC to 5v. So maybe my
question should be: How can I cap a 5-10v signal to 5v?
Click to expand...
There are CMOS gates that tolerate 0-10V input and can be
powered from 5V; the venerable CD4050 is a CMOS hex noninverting
buffer of this type that is old enough to have teenage kids.
There are undoubtedly one-gate versions, too.
 
On Fri, 02 Sep 2011 09:32:59 -0500, "krw@att.bizzzzzzzzzzzz"
<krw@att.bizzzzzzzzzzzz> wrote:

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

On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb
steveklett@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.
Click to expand...
---
Mea Culpa.

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

--
JF
 
John Fields wrote:

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


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


On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb
steveklett@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?
Click to expand...







10 V
+
|
|
|
1k +
___ |/
IN -|___|----+----|
| |> OUT
| +-----------+
+
|
\ o
\ Jumper Select
\.
o
|
|
.-.
| |
| | 1k
'-'
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

I Like this idea better.

Jamie
 
"Tim Wescott"
Note that all of the suggestions so far are to some extent kinda slow --
if really snappy action is necessary (and you can somehow get it out of
the DAC), then point this out.
Click to expand...

** A two resistor divider need not be slow. A small value cap across the top
resistor to balance any stray capacitance loading the mid point will remove
any delay.



..... Phil
 
On Fri, 02 Sep 2011 19:15:07 -0500, John Fields
<jfields@austininstruments.com> wrote:

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

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

On Thu, 1 Sep 2011 22:27:29 -0700 (PDT), SklettTheNewb
steveklett@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,
Click to expand...
$6.34 in thousands.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM136H-5.0-ND

That is, if you're talking about an LM136-5 (that you can actually buy). An
LM286 is an opamp. You've really pulled your pud on this one.

but what have you got that's less than
half a penny?
Click to expand...
Two 0603 resistors. Two tenths each.
 
On Fri, 02 Sep 2011 21:45:37 -0400, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

John Fields wrote:

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


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


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









10 V
+
|
|
|
1k +
___ |/
IN -|___|----+----|
| |> OUT
| +-----------+
+
|
\ o
\ Jumper Select
\.
o
|
|
.-.
| |
| | 1k
'-'
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

I Like this idea better.
Click to expand...
Why bother with the follower? It's slower than crap, and may not work,
without a pull-down (leakage). In any case, it's a useless part.
 
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