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priyank wrote:
> Hi Chris
>
>
> I spent 5-6 hours trying to get the thing workiI am sorry to the forum
> if you guys thought i was trying to get my homework done. Trust me that
> was not the case. Its just that i am frustrated with this silly little
> thing and i am not sure whats wrong with my circuit!
> ng and get rid of noise and get clean signal!
>
> I have now decided to chuck mpx2050gp out and get ASDX015D44R, its gona
> cost me fortune but i wannt this thing working.
>
> http://au.farnell.com/jsp/search2/browse.jsp?N=500001+401+1001501&No=50&Ns=PLS_SKU%7c0#results
>
> http://www.farnell.com/datasheets/60901.pdf
>
>
> Guys u wannt believe but in AUstralia i am not able to find mpx5050gp
> and neither the amplier u suggested.
>
> Dspace card does take in negative supply but then to I will surely get
> rid of AD622 and get a single supply amplifier as per ur suggestion.
>
> I have bought the LM324 as per the apllication notes and will get the
> filter soldered on veroboard tonight.
>
> WIth the filter i surely agree have lot of work needs to be done! I am
> really confused about what filter would be best for my circuit!Ill
> again go through the textbooks today
>
> I have got the pictures of th output waveform which i am getting on the
> scope(i am first trying to check circuit on oscilloscope) and ill try
> post the link for pics within next 5 hours.(lol... it will atleast
> prove im trying and not trying to get my homework done).
>
> Chris i appreciate ur help and not even my best mates would have helped
> me so much.
> (sorry bout my spelling errors!)
>
> cheers
> priyank
priyank wrote:
> Hi Chris
>
>
> I spent 5-6 hours trying to get the thing workiI am sorry to the forum
> if you guys thought i was trying to get my homework done. Trust me that
> was not the case. Its just that i am frustrated with this silly little
> thing and i am not sure whats wrong with my circuit!
> ng and get rid of noise and get clean signal!
>
> I have now decided to chuck mpx2050gp out and get ASDX015D44R, its gona
> cost me fortune but i wannt this thing working.
>
> http://au.farnell.com/jsp/search2/browse.jsp?N=500001+401+1001501&No=50&Ns=PLS_SKU%7c0#results
>
> http://www.farnell.com/datasheets/60901.pdf
>
>
> Guys u wannt believe but in AUstralia i am not able to find mpx5050gp
> and neither the amplier u suggested.
>
> Dspace card does take in negative supply but then to I will surely get
> rid of AD622 and get a single supply amplifier as per ur suggestion.
>
> I have bought the LM324 as per the apllication notes and will get the
> filter soldered on veroboard tonight.
>
> WIth the filter i surely agree have lot of work needs to be done! I am
> really confused about what filter would be best for my circuit!Ill
> again go through the textbooks today
>
> I have got the pictures of th output waveform which i am getting on the
> scope(i am first trying to check circuit on oscilloscope) and ill try
> post the link for pics within next 5 hours.(lol... it will atleast
> prove im trying and not trying to get my homework done).
>
> Chris i appreciate ur help and not even my best mates would have helped
> me so much.
> (sorry bout my spelling errors!)
>
> cheers
> priyank
Hi, Priyank. OK. I'm assuming you're in an electronics course of some
kind, but I might be wrong. If you wouldn't mind, could you mention
whether you're in a trade school or college, you are an electronics,
computer programming or biology major, what's this class, and what
level class this is.
Here's the deal. If you put something together on a board and plug it
in, it *always* works. If flames are erupting from your board, if
power is hooked up backwards, if you've got everything miswired, it's
still working -- it's still doing exactly what you made it do. You may
have wired it up wrong, you may have hooked up power backwards, but
it's just obeying the laws of physics and the way the chips and
components are designed.
If your circuit isn't doing what you want it to do, you might not
understand what it's made to do. You might not have followed the
correct procedure to get it to operate properly. You may not really
understand what you want. But the problem is you, not the silicon or
wire or metal film or electrolyte and foil, even if there's smoke
pouring from your breadboard. Especially if there's smoke pouring from
the breadboard.
You should be able to cobble together something that works fairly
quickly. You have the sensor and the ICs right now to make something
happen now. An AD622 is a great IC -- it just happens to need dual
power supplies, which might not even be a problem for you. Wire up
your AD622 with the gain set resistor on a small piece of perfboard,
and mount it right next to the sensor (less than an inch away). Now
the venerable LM741 is easily capable of doing the job of the LM324 on
the other side of the 4-conductor wire (near your DAC board) if you
have dual power supplies. Look here:
|
| DAC Board
| .------------.
| Sensor Instr. | |
| Amplifier | |
|.--------. .----------. | |
|| 0-40mV | |Av = 1000 | | |
|| output | | | | |
|| | | o--o---------------o A |
|| | | | | | |
|| o---o | | | |
|| | | | | | |
|| o---o | | .---------. | |
|| | | | | | Filter/ | | |
|| | | | | |Amplifier| | |
|| | | | | | | | |
|'--------' '----------' '--o o--o B |
| | | | |
| '---------' | |
| '------------'
|
|
|
|
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)
This is easy.
Your basic cut 'n' paste circuit can be logically divided into blocks.
Look at block 1. It's the sensor. It gives a 40mV differential output
for 0-50kPa. OK. Disconnect the outputs from everything else, power
it up, and then just put a DVM across the inputs while you apply some
air pressure. If you see a millivolt signal, at least you know it's
kind of working. If not, you may likely have smoked it, either now or
before. If these are school samples, they may have been donated from a
broker who had problems with them and decided to get a tax writeoff for
the lot -- it's conceivable you got the one bad one in the lot. No
output? Get another one.
OK. Now look at block 2, the IA. You've chosen a resistor for a gain
of 100 (0-40mV to 0-4V). Does it work? You can reconnect the sensor
if you want and apply that pressure again, or you can just ground one
input and apply a millivolt signal to the other (if you don't have
anything handy, a "D" battery, a series resistor and a pot will make a
good one). Apply a 30mV input. Do you get a 3V output? Does it do
what you think it should do? If not, feel/smell for a hot IC, recheck
your wiring, look at every conceivable way you could have messed it up
before you conclude the IC is bad. If it is, you probably smoked it
before. Get another one. Use your meter. Use your head.
Now look at the filter section. It blocks DC. It lets AC pass. If
you don't have a function generator or any other lab equipment, just
hook up a low voltage transformer, and use a series resistor and a pot
to apply a 60Hz signal of about 2mV at the input of the filter. If you
wired it up right, you should see a large amplitude 60Hz signal at the
output. If you look at the app note, it says the Fig. 1 filter is
amplifying the millivolt signal up to tenths of a volt, so you should
see some good gain here.
Once you've gotten to this point, disconnect the sensor again, and
ground one side of the IA. Apply a 30mV DC voltage with a 1/4mA AC
signal riding on it (battery, transformer, series resistors will do
fine -- just apply your basic DC circuit theory you must have had
sometime before you got into this class). Look at the output of the IA
and the output of the filter amplifier. Do they work together?
This is a basic reality check on your stuff -- is it smoked, or does it
work. If I had your circuit on a board in the lab, I'd do this first.
With decent lab equipment, it wouldn't take more than a few minutes to
find all this out.
You've gotta walk that long road alone. And you've gotta use the tools
you have, including your head.
Git R Done
Chris
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