# Arduino Uno: Ground all Ground of DC supplies together: Should or Shouldn't

Hello,

I am currently using Arduino Uno to control intensity levels of 3 color channels of my light. The intensity levels can be adjusted by controlling three 0-5VDC inputs into pin A0, A1 and A2: 0V means 0% intensity and 5V means 100% intensity. And the light is so sensitive that a step of ~10mV could change some brightness of the light.

I use three 0-5VDC power supplies to adjust the intensity level; and since I want all the GRD of those power supplies and GRD of my Arduino to be the same, I tie all those GRD together.

From school, I learn that DC voltage is basically a difference voltage between A&B. Since A&B on the 3 different power supplies are different, how should I solve the issue?

For example three 5VDC power supplies:
Power Supply 1: A= 0.5V and B = 5.5V
Power Supply 2: A= 0V and B = 5V
Power Supply 3: A= 0.3V and B= 5.3V

Shall I connect all those A (as negative pin or GRD pin) together? Any thought to bring down all A to be GRD together?

You should always tie all the grounds together, unless there is some specific reason to avoid doing so.

Power supplies generally do not have terminals labelled “A” and “B”.

What exactly do you mean by measuring voltages on these terminals? From what points are you measuring these voltages? Any single terminal does not have a specific voltage; you measure its voltage compared to a reference point. So what reference point are you using to measure?

Clearly you need to explain to us what these power supplies are. Easiest by giving a Web link to the description where you purchased it.

Power Supply 3: A= 0.3V and B= 5.3V

Looks like a 5V supply that has been measured with reference to some other voltage. That probably hides a mistake. As asked above, how did you measure these?

Provided that you could measure voltage differences between the Arduino Gnd and the A terminals, reproducible values suggest that the power supplies are already tied to some kind of ground (ground loops?). To find out more, measure the short circuit current flowing between the A pins, and between Arduino Gnd and the A pins. Considerable currents (>1mA) discourage concurrent use of these supplies.

If currents on ground lines shall be kept to a minimum, the power supplies can be connected to their dedicated motor driver or other power consuming modules. Then the modules' Gnd and signal lines can be connected to the Arduino in a star topology, so that only the signal currents run over these lines.

DrDiettrich:
Considerable currents (>1mA) discourage concurrent use of these supplies.

On the contrary, currents more than 1 mA merely mandate that the grounds be tied together with reasonably heavy wire.

In fact, you would actually be more concerned with AC currents which are not as easy to measure.

I - like aarg - was actually trying to extract some useful information from the OP before offering "solutions" for problems that he appears not to comprehend, so that we can first help him with the implicit gaps in his knowledge.

It's (yet) another form of "XY problem"; running before learning to walk.

Thank you for taking a look into my problem.

For A and B terminals that I mentioned earlier means a negative and positive outputs right at the DC power supplies. And the example earlier is measured between GRD of the Arduino to each point A (-) and B(+) of the power supplies.

For the clarification:
V(between GRD of Arduino to GRD of each power supply) are different and vary from around ~0.043. And since I might use different types of power supplies later, even using PLC to replace those power supplies, I wondering if there's a way to pull all those GRD (GRD of Arduino and GRD of all power supplies) down to 0.

In case you wonder what power supplies I am using:
CSI5003X5 : https://www.circuitspecialists.com/bench-power-supply-csi5003x5.html
CSI3003X3 : https://www.circuitspecialists.com/bench-power-supply-csi3003x3.html?otaid=gpl&gclid=CJCn8d-gw80CFQ6GaQodJS8GiQ

What do you think?

Thanks,

You should know that current deserves 2 lines to flow, one from the source to the consumer (DVM...) and one back to the source. If you only connect a DVM between Arduino Gnd and A, where should be the line back to the power supply? It's like you measure one pole of a detached battery against Arduino Gnd, what value would you expect then?

If your supplies have an USB port, for remote control, and that port is plugged into the same PC as the Arduino is, that connection establishes that second line.

But apart from that, if you need 3 adjustable voltages for the RGB intensities, I'd use 3 pots between Arduino Gnd and Vcc, and attach their wipers to 3 analog inputs.

Right, now we get to the bottom of the matter.

These are variable voltage bench power supplies.

They are designed so that neither negative (black) nor positive (red) is connected to ground (green). You have the option to connect one or the other to ground as you require. If you do not do so, there will be some floating voltage on the negative terminal if you measure it with a meter of sufficiently high input impedance - as most digital meters are.

But keep in mind - these supplies are meant to have one or other input terminal connected to ground as you decide. And it does not matter which ground, so the ground on your Arduino (which I presume is connected to your computer or laptop) is as good as any other ground. So just connect all the grounds (negatives) together - at the Arduino board.