This has been troubling me & I just can't wrap my head around the best way forward.
Two units, each have their own PSU via a wall wart - each have different voltages (it I understand this correctly, in this wall wart scenario, their actual ground isn't *true* ground).
Not that it's particularly relevant - The first unit takes a small analogue signal & amplifies it. The second unit processes the analogue signal.
I want to put in a bit of bespoke circuitry between the two units.
My problem? How to physically connect to the two different units that have different grounds & rails! (ideally I'd like to source the voltage for my little circuit from the second unit which only has one 9V rail)
Maybe it's a simple solution?
The output of the first unit is really just an opamp output, the opamp has dual rails.....+7V & -7V. The unit's output signal will obviously be referenced to the unit's 'pseudo-ground'
The input to the second unit is also an opamp, but this time is a single supply +9V....once again with a pseud-ground.
Is it just a matter of 'commonising' (is there such a word?!) the units' grounds (even though they are in effect different becuase they aren't a true 'common' ground), with a cap in the signal path to DC decouple them?
Two units, each have their own PSU via a wall wart - each have different voltages (it I understand this correctly, in this wall wart scenario, their actual ground isn't *true* ground).
Not that it's particularly relevant - The first unit takes a small analogue signal & amplifies it. The second unit processes the analogue signal.
I want to put in a bit of bespoke circuitry between the two units.
My problem? How to physically connect to the two different units that have different grounds & rails! (ideally I'd like to source the voltage for my little circuit from the second unit which only has one 9V rail)
Maybe it's a simple solution?
The output of the first unit is really just an opamp output, the opamp has dual rails.....+7V & -7V. The unit's output signal will obviously be referenced to the unit's 'pseudo-ground'
The input to the second unit is also an opamp, but this time is a single supply +9V....once again with a pseud-ground.
Is it just a matter of 'commonising' (is there such a word?!) the units' grounds (even though they are in effect different becuase they aren't a true 'common' ground), with a cap in the signal path to DC decouple them?
Yes, your reference voltage should always be tied together and be used as a reference throughout the system.
Andre Visser said:
I'm not sure I fully understand the way you've written that?
Are you saying I should combine the two separate
grounds together? (one from each unit)
Yes, on the one unit you created +7V, 0V and -7V and the other 0V and +9V. The 0V of each unit should be directly connected.
Many thanks.
So I take it, the fact that they're not both the same 0V (versus say a true 'common' ground), but each is merely 0V relative to their respective unit's rails, that there's no issue joining them together?
So I take it, the fact that they're not both the same 0V (versus say a true 'common' ground), but each is merely 0V relative to their respective unit's rails, that there's no issue joining them together?
Correct, if not connected these two 0V lines could float to any voltage relative to each other. You must create a common by connecting them together.
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