[SOLVED] Schematic problem: Virtual GND or GND

[alekvodnjan]

Hy friends!
I have few very simple questions that I'm confused about.
As you can see in the schematic bellow some pins are connected to Virtual GND and some to -12 V (reffered as 0 V on schematic)



Why red marked ones are not connected to Virtual GND on schematic? For example, shouldn't PIC's Vss, be connected to real 0 V and not to -12 V like on this schematic ? What will happen if we connect all marked pins to Virtual GND?

Thanks!

 

[FvM]

The main problem is that the virtual ground isn't designed to source or sink DC current. Loading it with the processor supply current would cause severe inbalance.

 

[alekvodnjan]

Thanks for answering me!

So everything is fine with this schematic?
I was in doubt that red marked pins are connected wrong... The problem was that always until now, I have seen schematics with PIC's Vss connected to 0 V (ground) and not to -12 V. Same with 7805...

 

[ravindragudi]

@ FvM
I couldn't understand the configuration of creating the virtual ground, can you please explain a bit?
Also, if the PIC is referenced with 0V, will it not exceed the operating voltage limit?

 

[alekvodnjan]

Ok then. First of all, I didn't project this schematic so I don't know all the reasons why this schematic is as it is.
Virtual ground is created for getting + and - 12V from 24 V DC Adapter. +-12V are required for supplying Op-amps.
I don't know the answer to second question because I'm asking myself the same. Also, pay attention to this: 0V is just a mark on schematic. It is not real 0 V.

 

[trust_me]

The 0V should be having 0V. Because the 24V adapter negative terminal is connected to the 0V node.

 

[ravindragudi]

Ok then. First of all, I didn't project this schematic so I don't know all the reasons why this schematic is as it is.
Virtual ground is created for getting + and - 12V from 24 V DC Adapter. +-12V are required for supplying Op-amps.
I don't know the answer to second question because I'm asking myself the same. Also, pay attention to this: 0V is just a mark on schematic. It is not real 0 V.

Thanks, but how will the opamp function with virtual ground if it is not sourcing or sinking any current? confused about this ...
Also, why the 24V supply is not used to generate dual supply of +12, -12 as required for the circuit operation?

I understood how the 5V is coming at the PIC, earlier I was confused with the -ve sign at the 24V input and was thinking that as -ve supply of 12V. The 7805 is getting 24V input and providing 5V at the output. Perfect !!

 

[alekvodnjan]

Thanks, but how will the opamp function with virtual ground if it is not sourcing or sinking any current? confused about this ...
Also, why the 24V supply is not used to generate dual supply of +12, -12 as required for the circuit operation?

Op-amps work fine. Tested with real circuit.

Adapter is used because device is portable. But there is no difference if you use battery, adapter or voltage supply. You must have virtual ground to get +- voltage from + voltage source.

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I must have virtual ground for Op-amp refference