# I need a little help with designing a Circuit!

Discussion in 'Electronic Design' started by [email protected], Jan 25, 2006.

1. ### Guest

Hey I need a little help with designing/drawing a circuit. Can someone
make me a sketch or help me with the solution?

Here is the my problem:
I'm going to make a measurement system for a bridge (AC bridge
circuit). The measure-elements in the bridge can be resistive, for
example: a Pt-100-element for measuring temperature, or a strain gauge
for measuring pressure or power, or it can capacitive so that it can
measure air humidity.
The bridge is going to be driven by AC, and shall be square-,
triangle-, or sinus-shaped. The frequency on the AC shall be in the
area from 400Hz - 1kHz. The reason for using AC is because we can
reduce influence of the amplifiers DC-error.
When the bridge is driven by AC-voltage, then of course the bridge's
output signal will be AC. And this output signal must be demodulated.
And the method I supposed use, is with Phase Sensitive Detection.

· Make an oscillator circuit to drive/operate the bridge.
· Make a necessary instrumentation amplifier by using op-amps.
· Make a phase shift circuit.
· Make a demodulator.

Terms:
· Assume that the bridge's output signal have amplitude = 2mV.
· The signal bandwidth is DC to 10Hz, -1dB with 10Hz.
· The measurement system shall be in the area 1.0V to 5.0V.
· The measurement system accuracy shall be ±0.5% of full scale.
· The measurement system resolution shall be 8 bits.

Component:
· Available supply voltage is +12V, -12V and +5V.
· Available op-amps are uA741, OPA27, OPA177.
· Available voltage reference is LM336.
· Available voltage comparator is LM311.
· Available analog switch is DG413DJ.
· Available DA-converters are DA0808, DAC0832.

2. ### Guest

Your professor. Let us know his email address, we will do the hard work
and forward your posting to him, then pass his reply on to you. Sound
good?

3. ### Jim ThompsonGuest

Sno-o-o-o-ort!

Sounds good to me ;-)

...Jim Thompson

4. ### Tim WilliamsGuest

Yeee-hew, I haven't ever seen one so obviously copy-and-pasted as that one,
wow!

Tim

5. ### Rich GriseGuest

Sorry, we don't do other people's homework for them.

How in the **** are you ever going to learn anything?

Good Luck!
Rich
<snipped homework assignment>

6. ### Rich GriseGuest

Sure, if he's offering \$160.00/hour, each, for our work. ;-)

Cheers!
Rich

7. ### Guest

When I was in first year physics 500 years ago, my lecturer said "Take
a look at the person on the left, and the person on the right. Get to
know them now, because by next semester, they'll be gone". The OP is
clearly one of the 2/3rds "goers".

(I cannot believe this, but there are kids in some of the classes I've
taken recently who are taking these courses for the THIRD OR FOURTH
time! How is this possible?!)

8. ### Guest

Oh, no, this is pro bono. In fact, I would be willing to invest in a
foreign-language dictionary for the OP's native language, if necessary,
to communicate with this professor

9. ### Dirk Bruere at NeopaxGuest

No problem.
Standard charge of \$60 per hour will apply.
Get back to me if you wish to continue.

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org

10. ### Guest

You're way too cheap; even I charge more than that, and everyone is
only too happy to tell me what scum I am.

11. ### martin griffithGuest

Hi Tim,
You missed this Cut 'n Paste from CAE

quote
I want to understand how exactly is an image(compiled
c code and loaded into memory) stored in memory.

What exactly is a linker script?

I work with a lot of c code on a daily basis but I really
don't understand :

How exactly the sections
like "text,bss,data etc."
work?

What exactly are they?

I believe the linker script describes this layout.

What exactly is a 'bundled image'?

What exactly is 'microcode'?
What exactly is 'firmware'?

I admit I use these terms myself pretty often,but
without much clarity.

Anyways any information or pointers(internet urls) in
this regard would be very helpful.

If it helps,my work involves a lot of driver code
in C on systems using MIPS processors.

Thanks a bunch....
/quote

martin

12. ### Spehro PefhanyGuest

Commendable. That generous spirit of 'giving' that is so rare these
days.

However, I feel compelled to point out that the native language of the
OP may not be understood by his or her professor. ;-)

Best regards,
Spehro Pefhany

13. ### JoergGuest

Hello Lwein,
Sometimes I wonder what the next generation EEs is going to be like. Not
being able to solder is one thing and that's already pretty bad, not
doing their homework on their own is worse, I guess.

I got my degree in Germany. There you couldn't do that because of a
three strikes rule. Twice was ok but only one course exam out of all of
them could be taken three times. Fail that and they'd freeze you for
good. And not just for that university but for all of them in that
country. The only way out would be going outside country or starting all
over in a different discipline. Going outside the country came with the
added benefit of first having to learn yet another language.

Regards, Joerg

14. ### Guest

I am sitting in classes with them right now. The outlook is not good.

Now, if I were to take them in to work with me and let them experience
one or two days of paperwork, managing QA, UL submissions, and putting
out fires, I think I could persuade all of them to change career paths
and become chefs, jugglers, prostitutes, bank robbers, confidence
tricksters, mimes, etc.
The teachers are not entirely absent of blame. My computer science
lecturer the other day told me that there is no point to learning
anything about analog, because everything these days is available in a
monolithic chip. Of course, this rather neglects the minor issue of how
your signals are to cross the great barren desert on the PCB between
two such chips. What else to expect from a computer science guy?
I guess it's more commercial here. It's roughly \$20,000 (average) per
year to attend a private university. \$5,000 per year to attend a city
university, but I don't know if any of them are ABET. I wouldn't be
there unless my employer was paying

The real question is, how it is even possible to fail these courses so
many times? Merely leaning one's face on the textbook and sleeping on
the page transfers enough knowledge to pass the exams. My dog could get
a 3.5 GPA in these courses.

15. ### Jim ThompsonGuest

Do you think these ne'er-do-well "students" will be able to hold a
job?

What puzzles me is the lack of enthusiasm. When I was a student I
couldn't get enough information. I was constantly scribbling ideas on
to paper.

I regularly take on projects today where I don't have a clue, but I'll
learn, and I often end up the expert ;-)

I LIKE electronics... it's FUN!

...Jim Thompson

16. ### Guest

Cultural. Engineering is not cool to teenagers. The US govt - or
somebody - needs to address this issue. Putting up a few posters in
school saying "science is for girls too" is not doing anything.

One doesn't become a good engineer without an attitude that "doing
things is fun", particularly things that involve lots of intense and
difficult work. A love of puzzles is a good quality too.

I work with a lot of engineers, practically all of whom are simply
waiting for something - either next week's paycheck, retirement, or a
new job. They cannot understand why I would be disheartened by a boring
month of no design challenges - after all, my checks keep coming, don't
they? I can see a lot more people like this coming down the pipeline...

17. ### GenomeGuest

Hey I need a little help with designing/drawing a circuit. Can someone
make me a sketch or help me with the solution?

Here is the my problem:
I'm going to make a measurement system for a bridge (AC bridge
circuit). The measure-elements in the bridge can be resistive, for
example: a Pt-100-element for measuring temperature, or a strain gauge
for measuring pressure or power, or it can capacitive so that it can
measure air humidity.
The bridge is going to be driven by AC, and shall be square-,
triangle-, or sinus-shaped. The frequency on the AC shall be in the
area from 400Hz - 1kHz. The reason for using AC is because we can
reduce influence of the amplifiers DC-error.
When the bridge is driven by AC-voltage, then of course the bridge's
output signal will be AC. And this output signal must be demodulated.
And the method I supposed use, is with Phase Sensitive Detection.

· Make an oscillator circuit to drive/operate the bridge.
· Make a necessary instrumentation amplifier by using op-amps.
· Make a phase shift circuit.
· Make a demodulator.

Terms:
· Assume that the bridge's output signal have amplitude = 2mV.
· The signal bandwidth is DC to 10Hz, -1dB with 10Hz.
· The measurement system shall be in the area 1.0V to 5.0V.
· The measurement system accuracy shall be ±0.5% of full scale.
· The measurement system resolution shall be 8 bits.

Component:
· Available supply voltage is +12V, -12V and +5V.
· Available op-amps are uA741, OPA27, OPA177.
· Available voltage reference is LM336.
· Available voltage comparator is LM311.
· Available analog switch is DG413DJ.
· Available DA-converters are DA0808, DAC0832.

You need to start out with a block diagram of your system. Paper is good for
this if you have a pen.

This is called top down design.

Take one sheet of paper and, from left to right, draw three boxes on it.

Label the left box 'Input Drive'.

Label the middle box 'Bridge'.

Label the right box 'Measurement'.

Or you can do it the other way around......

Once you have done that then you have your top level design.

BUT..... ask yourself 'What might be missing?'

Hint, begins with C and is not Cuntrol.

Throw your original piece of paper away and do it again but this time
include the 'not Cuntrol' block.

Does it look good?

DNA

18. ### Jim ThompsonGuest

de-lovely ;-)

...Jim Thompson

19. ### Joseph2kGuest

Like hell! I can't afford to do this for less than \$250/hr + \$100/per 8.5
by 11 inch page.

20. ### Dirk Bruere at NeopaxGuest

It costs me approx \$20k per year for me to live very comfortably.
Now check out how much I have to work...

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org