Floating Grounding

Other Hardware General Electronics
1

Hi everyone,

I use an Arduino nano to send logic signals to some RF switches.
Digital pins d1-d4 are always high and I use push buttons to interchange between High and Low states manually (I forgot to mention on the drawing)

The voltage dividers are on a PCB and have a common ground (ground plane)

In general the circuit works fine but once I forgot to connect the ground on the PCB and I noticed that when the ground is unconnected (I think this is called floating grounding?) the voltage divider does not work and the output of the voltage divider is equal to the input, therefore 5V (for HIGH digital input). In addition when the ground is unconnected and for example d1 is HIGHT while d2-d4 are LOW I have got the same potential (5V) on each voltage divider output :o

I want to understand why this is happening? When the ground is connected and everything is working fine...I know that ground is the returning path bus still I cannot understand this performance

I am not sure If my question is really clear, so please let know for further detail.

Thanks is advance

2

Do you know how a voltage divider works? It simply follows ohms law :slight_smile: Aka, you need a (small) current trough the resistors for them to drop voltage. No current = no voltage drop.

Nikosant03:
In addition when the ground is unconnected and for example d1 is HIGHT while d2-d4 are LOW I have got the same potential (5V) on each voltage divider output :o

All GND's of the voltage dividers connected together but not connected to GND?

I would expect a voltage on the divider with a LOW because if you redraw it you can see a path from the HIGH to the LOW pin. Aka, forming voltage dividers. But can't be 5V.

3

If its floating, its by definition not ground.

4

septillion:
All GND's of the voltage dividers connected together but not connected to GND?

All grounds of the voltage divider are connected through the ground plane on the PCB

I power the Arduino through an external power supply and during the experiment I forgot to ground the ground plane of the PCB with Arduino's ground.

So I didn't provide a return path from the PCB back to the Arduino...

5

6

Yeah, so effectivly you created voltage dividers between the different IO pins :slight_smile: