Opamp as adder

Tip / Sign in to post questions, reply, level up, and achieve exciting badges. Know more

cross mob
lock attach
Attachments are accessible only for community members.
Anonymous
Not applicable

 Hello,

   

            i am trying to work opamp as "adder" (adding two analog signals with different frreq) ,but i am facing some errors in connecting resistors to the analog input pins. Please say how to avoid this.

   

I have shown the schematic diagram and errors in pic

0 Likes
11 Replies
Bob_Marlowe
Level 10
Level 10
First like given 50 questions asked 10 questions asked

You did not connect your resistors to the annotation-terminal of the pin_1 and pin_2 and the pins are not connected to any wires in the PSoC.

   

 

   

Bob

0 Likes
ETRO_SSN583
Level 9
Level 9
250 likes received 100 sign-ins 5 likes given

If you view the "notice" list after a compile you can double click most error

   

notices and the error will be highlighted on schematic so that you can easily

   

identify and correct it.

   

 

   

Regards, Dana,

0 Likes
lock attach
Attachments are accessible only for community members.
Anonymous
Not applicable

 now i connected the resistors to the annotation-terminal of the pin_1 and pin_2 and i am giving the two analog signals(inputs) to these Pins ,but still after debug the tool is showing some notes ....i have shown that in pic. how to avoid this notes?

0 Likes
Bob_Marlowe
Level 10
Level 10
First like given 50 questions asked 10 questions asked

Well, the message states exactly what the situation is: the pin is unconnected.

   

You are mistaking the "inner" side and the "outer" side of the PSoC: The OpAmp is within the PSoc, all blue components and lines are outsides of the PSoC, so probably you do not need pin_1 and pin_2 and connect your signals to be added directly to your external resistors.

   

 

   

Bob

0 Likes
Anonymous
Not applicable

 It means the resistors which are in the PSoC creator doesn't like resistors in the circuit???

   

should i connect resistors externally also? 

0 Likes
Bob_Marlowe
Level 10
Level 10
First like given 50 questions asked 10 questions asked

You have got the resistors from the "Annotation" tab in the components window, these are NOT resistors within the PSoC, they are used to clarify / document the external connections of your PSoC design.

   

You will have to provide these resistors in reality and connect them to your pins and your signals.

   

Draw a line, everything that is blue is not within your PSoC chip and has to be connected externally.

   

 

   

Bob

0 Likes
lock attach
Attachments are accessible only for community members.
Bob_Marlowe
Level 10
Level 10
First like given 50 questions asked 10 questions asked

You may even save a pin when you use an internal voltage reference set to GND, look at attached project built with Creator 2.1

   

 

   

Bob

0 Likes
ETRO_SSN583
Level 9
Level 9
250 likes received 100 sign-ins 5 likes given

Your Vref wants to be Vdd/2 or an internal (bandgap) derived Vref (some multiple therof)

   

in order to maximize OpAmp output swing and place it in its CM range.

   

 

   

Regards, Dana.

0 Likes
lock attach
Attachments are accessible only for community members.
ETRO_SSN583
Level 9
Level 9
250 likes received 100 sign-ins 5 likes given

Somethimg like this, attached.

   

 

   

Regards, Dana.

0 Likes
lock attach
Attachments are accessible only for community members.
Anonymous
Not applicable

 Hello,

   

   My schematic diagram is shown in Pic,In that I am adding two signals ,to get the correct output of “OPAMP”  I should give some offset to the input signals,here output of OPAMP also producing some offset. If I give this output of OPAMP(with some offset) to the ADC I won’t get correct output.

   

Should I always use some level shifters for every output of a component???

0 Likes
ETRO_SSN583
Level 9
Level 9
250 likes received 100 sign-ins 5 likes given

You have to offset the OpAmp so that your swing will produce

   

an allowed CM range swing on output. Thats if your input is

   

symmetrical about ground.

   

 

   

If you input is always - then you may not need offset. Or

   

for all + input signals you do not care OpAmp output is fixed

   

at ground, you are only measuring - input signals.

   

 

   

All analog components must have their input CM range met, normally

   

one level shift at the signal input accomplishes that.

   

 

   

The example I showed in previous post is for a signal whose input

   

is symmetrical about ground.

   

 

   

Regards, Dana.

0 Likes