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

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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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...

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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

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

Partially...

For the 5µF capacitor: it's connected correctly in schematic, but I'm not sure you will found a value of  5µF, but a value of 4,7µF, 10µF, 22µF, 47µF... are standardized values . Did you check if you use the good package ? often this king of capacitor have a cylinder shape, and it polarized (+ shoufd be connected to +24V, and - to GND)

A good advice would be to found a capacitor (buy it or at least found were you will buy it), so you be sure of the value, the dimensions, the shape, if it's polarized or not....

The physical position on the board doesn't really mater for that capacitor.

For the 2 others, It's NOT OK: you need only one capacitor, and it should be in parallel not in series with LM324 :

     -> in schematic : you connect the +V pin (pad number 4) of the LM324 directly to +24V, and do the same with the GND pin (pad number 11), connect directly to GND. Then you add your 100nF capacitor and connect one pin to +24V, the other one to GND

     ->  in board, you place physically this capacitor near the LM324, the nearest is the best.

The role of these capacitor is :

- filter noise coming from your supply.

- provide a local reserve of energy for you amp : when the amp will need to swing is output, it will sink current, and will need fast, and if there is no capacitor around, the current will flow from your supply through your cable and the copper of your board. With ideal wire no problem. but in real life, they have a little resistance and inductance: both will slow down current flow, and the voltage of the supply near the LM324 will goes down....

That why a good practice is to add :

- 1 huge capacitor (10µ - 100µF) for the board: it's provide energy for 'slow' consumption raises, and filter low frequency noise from the power supply...

- 1 little capacitor for each integrated circuit (chip), near the chip,  for fast consumption variations, and filter for higher frequency noise...

This is only a very very simplified explanation and complex design need more than this little cook book, but in you case that could be a good start !

That also why you need to have larger wire for supply than for the other signal.

Guillaume.

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...

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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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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.

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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

 

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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.

 

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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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.

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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:

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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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