should i connect the different grounds?

Design Concepts
1

Hi!

in the new midibox unit that i’m, building  i will integrate my breath controller (BC) unit, designed years ago.

this time, the BC unit will be inside the box, with a connector to the breath sensor.

the BC PCB is powered by a circuit similar to the core one, but with 8V instead of 5.

the main power supply will be the same for both core and BC.

but i want to keep the power units separate, in the sense that the main supply will power in parallel the core and the BC.

the other solution would be to connect first the BC and then, from its 8 volt, the core. but i’m not sure about the current required (ince this time i have a backlit LCD) and i fear that the 78L08 used in the BC will heat too much.

so, the “big” question is: should i connect the two grounds of the core and of the BC?? i think that this would be a good idea… i’m wrong?

beside this, i’m using the 8V from the BC to power up a simple gain circuit (made with a LM324) that will “boost” the signal acquired form an old PC recycled joystick, that will be connectec to 2 analog in of the AIN module. i fear that, if the two grounds are not connected, there could be some problems in the accuracy of the analog signal that will come to the AIN module from the joystick…

thanks for the comments! :slight_smile:

2

A ground is a ground is a ground, it might not be “a ground”, but an arbitrary voltage level/point on circuit, where all the other voltages are referenced.

You’ll anyway need a reference voltage between the circuits, so AIN will detect voltage between this reference point and what it sees in AIN, right?

My guess for this reference point— ground it is?

Bye, Moebius

p.s. Uhhuh-- sorry for this sorta short “informative” (?!) post. Think ground as a current return path.

3

moebius is definately right.

as for analogue ckts (all ckts ?) generally  you should mind to avoid ground loops, means same ground symbol of your schem (whatever potential)

<->ground point on PCB <-> connect together on the possibly shortest way to the same physical point…

<crypt mode off>

avoid any type of ground circles so the electrons will not be in intellectual stuttering stress to find their way out

(some people call it  “hum” in the audio world)

;D

kind regards

Martin