Could someone check my design?

Am 07.10.2015 um 14:02 schrieb Jacob Thastrup:

Hi Guys

I'm totally new to this. I'm trying to build a 4 channel opamp (boost my

signal about 100x)

I'm hoping someone has the time to quickly check my design and see if it

makes sense and perhaps let me know how to improve it.

 

Thanks

Jacob

 

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Attachments:

opamp.zip

 

No capacitors?

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Mit freundlichen Grüßen / With best regards

Joern Paschedag

You mean to filter the input?

Hi,

At least capacitors should be added on the supply...

I don"t know the purpose of your circuit but you should add at least a small one capacitor (10 to 100 nF) placed near the power supply input pins of the LM324, and a electrolytic caacitor (few µF) rignt after the supply input connector.

En large 24V supply trace, and for the GND you can enlarge the trace or better add a GND plane (polygon).

Guillaume

The opamp is meant to amplify a 7-50mV signal around 100 times so I can reliably read it with a National Instruments DAQ.

I'm sorry I'm such a newbee, any and all help is really appreciated! I'll try and add some capacitors to the diagram and see if I can work out how to add a GND plane :-)

I'll be back ;-)

Thanks

Jacob

Hmmm not sure i got the capcitors right. ;-)

How's this version?

Thanks again

Jacob

Am 08.10.2015 um 14:43 schrieb Jacob Thastrup:

Hmmm not sure i got the capcitors right.

 

How's this version?

 

Thanks again

Jacob

 

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Attachments:

test4.zip

 

Where is your attachment???

Anyway I didn't like the many junctions and the separated connectors in

the schematic,

so I messed around in your design (as an example of course). Same went

for the board

I also changed the width of the tracks, because I suppose you want to

etch yourself...

--

Mit freundlichen Grüßen / With best regards

Joern Paschedag

Am 08.10.2015 um 14:43 schrieb Jacob Thastrup:

Hmmm not sure i got the capcitors right.

 

How's this version?

 

Thanks again

Jacob

 

--

To view any images and attachments in this post, visit:

http://www.element14.com/community/message/162771

 

Attachments:

test4.zip

 

Where is your attachment???

Anyway I didn't like the many junctions and the separated connectors in

the schematic,

so I messed around in your design (as an example of course). Same went

for the board

I also changed the width of the tracks, because I suppose you want to

etch yourself...

--

Mit freundlichen Grüßen / With best regards

Joern Paschedag

Hi Joern

Maybe I'm getting it wrong. But I don't see any files from you?

Thanks

-Jacob

Am 08.10.2015 um 17:38 schrieb Jacob Thastrup:

Hi Joern

Maybe I'm getting it wrong. But I don't see any files from you?

Thanks

-Jacob

 

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I attached it but I suppose it is the glorious interconnection between

the newsgroup and element 14 that never works since years...

Next try now...

--

Mit freundlichen Grüßen / With best regards

Joern Paschedag

Am 09.10.2015 um 10:42 schrieb Joern Paschedag:

Am 08.10.2015 um 17:38 schrieb Jacob Thastrup:

Hi Joern

Maybe I'm getting it wrong. But I don't see any files from you?

Thanks

-Jacob

 

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To view any images and attachments in this post, visit:

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I attached it but I suppose it is the glorious interconnection between

the newsgroup and element 14 that never works since years...

Next try now...

 

No, sorry it  didn't go throu, maybe because I'm not registered at

element14 .

And I'm not interested to register there.

--

Mit freundlichen Grüßen / With best regards

Joern Paschedag

On 09.10.2015 11:12, Joern Paschedag wrote:

Am 09.10.2015 um 10:42 schrieb Joern Paschedag:

Am 08.10.2015 um 17:38 schrieb Jacob Thastrup:

Hi Joern

Maybe I'm getting it wrong. But I don't see any files from you?

Thanks

-Jacob

 

--

To view any images and attachments in this post, visit:

http://www.element14.com/community/message/162826

 

 

I attached it but I suppose it is the glorious interconnection between

the newsgroup and element 14 that never works since years...

Next try now...

 

 

No, sorry it  didn't go throu, maybe because I'm not registered at

element14 .

And I'm not interested to register there.

 

You can find them here

http://www.eaglecentral.ca/forums/index.php/t/51848/5abd43c14367c14cffef482390e897d4/

Once again thank you guys!!

Guillaume, thank you for the explanation it really helps!

I've added a ground plane to Joern's design... does that make sense?

I hope you can see the attached file..otherwise I'll go register at eaglecentral as well.

-Jacob

Hi,

That last design is better, the ground plane is OK.. You remove the big capacitor  (your 5µF) I suggested to check the value and the package, but not t remove it ? If it was one of my design I would  put a 10µF electrolytic capacitor between GND and +24V, just right after the supply connector...

Nice work ....

Am 09.10.2015 um 18:34 schrieb Jacob Thastrup:

Once again thank you guys!!

Guillaume, thank you for the explanation it really helps!

 

I've added a ground plane to Joern's design... does that make sense?

 

I hope you can see the attached file..otherwise I'll go register at

eaglecentral as well.

-Jacob

 

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To view any images and attachments in this post, visit:

http://www.element14.com/community/message/162904

 

Attachments:

test5.zip

 

You should go there anyway. It is just the better link to the cadsoft

newsgroups

They don't have trouble with attachments (as you have seen).

BTW my "design" was just a suggestion.

Maybe you should add an electrolytic capacitor in general and foresee

some holes to screw this print somewhere.

--

Mit freundlichen Grüßen / With best regards

Joern Paschedag

Jacob Thastrup wrote on Fri, 09 October 2015 12:34

Once again thank you guys!!

Guillaume, thank you for the explanation it really helps!

 

I've added a ground plane to Joern's design... does that make sense?

 

I hope you can see the attached file..otherwise I'll go register at

eaglecentral as well.

-Jacob

 

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To view any images and attachments in this post, visit:

http://www.element14.com/community/message/162904

 

Attachments:

test5.zip

I think there should be a ground connection for each channel. In other

words, you will need 3-pin instead of 2-pin connectors. Otherwise your only

ground connection is through the power supply connector. The ground pin

should be between each input and output pin. I agree with others that you

should have a cap across the power supply terminals. Also, on your layout,

if you switch to a finer grid (i.e. 10 mil aka(0.01")), you can move some

traces slightly and improve the ground plane near the left end of the chip

(also changing the polygon width to 12 mils helps). If you swap the ends of

R5 and R6, then you can have a single trace for OUT3, instead of 2 traces.

You can do the same thing for the other channels.

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Guillaume barrey[1

wrote on Sat, 10 October 2015 05:53]Hi,

 

That last design is better, the ground plane is OK.. You remove the

big

capacitor  (your 5µF) I suggested to check the value and the

package,

but not t remove it ? If it was one of my design I would  put a 10µF

electrolytic capacitor between GND and +24V, just right after the

supply

connector...

 

Nice work ....

Ah ok hehe, I've added the 10uF capasitor now.

Quote:

I think there should be a ground connection for each channel. In other

words, you will need 3-pin instead of 2-pin connectors. Otherwise your

only ground connection is through the power supply connector. The ground

pin should be between each input and output pin.

I'm not sure I understand this bit.

The signal I'm trying to amplify is coming from small oxygen cells

(galvanic cells). If I understand what you are suggesting, is that I use

the GND from each cell to connect to their respective inverting input of

the opamp? My original idea was to tie all the GND lines from the cells

into the same GND connector (the one I also connect the power supply to).

Potentially a stupid question.. will that work? I don't need to ground

everything "together"?

Quote:

If you swap the ends of R5 and R6, then you can have a single trace for

OUT3, instead of 2 traces. You can do the same thing for the other

channels.

Cool, that does look better

Once again thanks for all the help!!

-Jacob

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Hi,

The sensor cell will produce a voltage, between the 2 signals :

- the signal you will connect to your amplifier input

- and the GND.

Only the voltage between these 2 signals (the difference) is important. The current that will flow out from your cell into the input of the amplifier is exactly the same than the current flowing from the GND of your board into the GND pin of your cell.

So, the role played  by the 2 wires of the oxygen cell (signal and GND)  is equivalent, and there is no reason to have a different path (except if GND is also used to supply the sensor see (*) ).

On the amplifier side : it amplifies the difference between the input signal and the GND plane, the GND plane is a REFERENCE.

If instead of connecting directly the GND of sensor to your board, you connect it to a point away from the plane (name it STAR point), with all the other sensor GND and supply GND, then you connect this start point to your board with a single wire. On the paper this will work.... but....

In this last GND segment (wire from the GND plane and star point)  you will have the sum of all the currents of all sensors, plus the current drained by the amplifier it self (and this last one is far more important than the others).

Where is the problem ?

The problem is that the copper is a good conductor, but not an ideal one !

You will have a little voltage difference between your GND plane and the start point, that will be dependent of that current, and the length of the wire, and so amplifier REFERENCE will not be exactly the reference of the sensor.

In other word, each signal will be polluted with the signal of the other cell and the consumption of the amplifier...

There is also other advantages of using same path for your sensor: you can use twisted pair wire, that way you reduce noise, specially if your sensor are far away from the borad.

Just one thing (*) : I don't know your sensor: is this sensor need a supply ? How this supply is wired? is the GND of sensor is only a output reference or also used for the return path of the supply ? because in that case you have to figure how best can the GND be wired.... there is no magic solution, and we can help you unless you give us more info...

Sorry with this very quick fast ultra simplified explanation... and if you want to have more fun... you can also question yourself about the output of your amplifier : How the GND path mcan be optimised and wired, on the output side (I suppose you will connect it to an acquisition device...)

Guillaume