Hi everyone,

I'm trying to design a voltage divider to power op amps. However, I'm in doubt if my schematic layout is correct as it uses 5V power from an Arduino instead of a double cell battery.

Please find my schematic below.

Another question is, for homemade etched copper pcbs with Perclorete. What should the trace width for power and signal be? 0.3mm for signal and 0.5 mm for power or 1 mm for both? How does eletromagnetic interference play a role in building noise in precision analog or digital signal applications?

Thank you.

 

As drawn you have problems. You have both ends of the voltage divider connected to 5V. If you ever connect GND in your schematic to ground for the Arduino, you'll also have problems.

Instead of showing us your proposed solution, why don't you tell us what you're trying to accomplish?

 

Why do you think you need a dual supply?
Often you can use op amps with a single supply, and just offset the signal to the middle of the supply voltage.
What op amps do you intend to use?
Can they operate from 5V?

 

Please find my schematic below.

If you going to use a virtual ground the resistor values need to be smaller and observe polarity on C5.

 

As drawn you have problems. You have both ends of the voltage divider connected to 5V. If you ever connect GND in your schematic to ground for the Arduino, you'll also have problems.

Instead of showing us your proposed solution, why don't you tell us what you're trying to accomplish?

Hi @dl324, I'm building an ecg amplifier. So the circuit needs to operate between +2.5V and -2.5V in order to reflect the negative parts of the ECG form. Right?

 

Hi @sghioto,

Sorry for my question, How do I draw that 5V + and - symbol on Kicad? Is it on the power library or symbol library?
You're right about C5, I didn't realize the polarity was wrong.

 

Sorry for my question, How do I draw that 5V + and - symbol on Kicad? Is it on the power library or symbol library?

I don't know.
Here's another virtual ground using an op amp.

 

Your resistors need to be size so that your midpoint stays close enough to the desired midpoint voltage under the maximum current that it will need to support.

 

I don't know.
Here's another virtual ground using an op amp.
View attachment 299816

Hi sghioto, I tried to make a modification on the schematic, similar to this one you showed me.
But when I go layout the board the OPAMPS still show powered by +5V and GND.

 

But when I go layout the board the OPAMPS still show powered by +5V and GND.

Are you measuring with respect to what you've called the Arduino ground? Or your virtual ground?

If you measure between the V+ and V- pins of the opamp, you'll measure 5V. If you measure with respect to the virtual ground, you'll get 2.5V on V+ and -2.5V on V-.

 

Are you measuring with respect to what you've called the Arduino ground? Or your virtual ground?

Hi dl324, the Arduino ground. It should show +2V5 and -2V5 on the pins when I go layout on kicad.

 

Hi sghioto, I tried to make a modification on the schematic, similar to this one you showed me.

Don't modify it use this circuit: Measure from ground to +5 volts and -5 volts

 

Hi @sghioto, it's because I don't know how to draw that +5V with a green wire and + and - poles. I searched but didn't find that symbol. Would you mind showing me how to draw that symbol?

 

Would you mind showing me how to draw that symbol?

I just copied the schematic and modified it in Windows Paint. Had nothing to do with Kicad.

 

the Arduino ground

Since you're "generating" the negative voltage from the Arduino supply, you can't have a negative voltage with respect to Arduino ground.

It should show +2V5 and -2V5 on the pins when I go layout on kicad.

Voltages are relative to whatever you're calling ground. You can have -2.5V relative to your virtual ground, but you can never connect your virtual ground to Arduino ground.

 

Hi Dennis, thanks for the clarification. I understand the concept of the relation of voltage and ground, however, I don't know how to draw it on a schematic for a PCB. Do you have any schematic examples?

 

'm building an ecg amplifier. So the circuit needs to operate between +2.5V and -2.5V in order to reflect the negative parts of the ECG form. Right?

Will the Arduino recognize a -2.5 volt signal?

 

I don't know how to draw it on a schematic for a PCB. Do you have any schematic examples?

Your virtual ground is just another net in the schematic. You can use any net name you want, but using GND will cause confusion, while Va wouldn't. You can avoid even more confusion by not using the ground symbol to represent it.

 

Hi everyone, I decided to change my power supply to a 9V battery (+4V5 and -4V5) as the OP AMPS can handle it and it's easier to layout on the schematic.
Thanks for the help everyone. I have to study more about virtual ground.