Connecting 2 different grounds related to 2 different voltage levels

[Emam]

Dear all,

I have a microcontroller (PIC) which I use to control :

- A stepper motor using a driver circuit working on 5VDC
- A force sensor working on 24 VDC

The microcontroller controls both the motor and the sensor.

I have connected the ground of the sensor, and the ground of my stepper motor (the driver), both to the ground of my microcontroller.

My questions:

- Is this correct? Can we connect 2 different grounds related to 2 differents voltage levels together?
- I see some noise or some fluctuations in the behaviour of my motor. Can the connection of 2 grounds be the cause for these noises?

Many thanks and bests regards
Emam

 

[Gryd3]

Dear all,

I have a microcontroller (PIC) which I use to control :

- A stepper motor using a driver circuit working on 5VDC
- A force sensor working on 24 VDC

The microcontroller controls both the motor and the sensor.

I have connected the ground of the sensor, and the ground of my stepper motor (the driver), both to the ground of my microcontroller.

My questions:

- Is this correct? Can we connect 2 different grounds related to 2 differents voltage levels together?
- I see some noise or some fluctuations in the behaviour of my motor. Can the connection of 2 grounds be the cause for these noises?

Many thanks and bests regards
Emam

To help reduce confusion, lets not call it a 'ground' ground is that stuff outside your window that the utility company sticks a rod into to provide 'ground'.

'common' on the other hand has nothing to do with the earth.
It is a good practice to pick a 'common' that will not interfere. A 'common' MUST be used to properly allow electronic to communicate with each other.
It is normal practice to share a common with multiple different voltage sources. A computer power supply does this for example. It's 'common' is shared with the +12, +5, +3.3, -5, and -12V lines as well as the signal wires. There must be a 'common' in order for the electronics to function. If you only connect a data wire, there is no reference to measure the state of the data wire from it it may behave irrationally.

*There is a potential GOTCHA! though... This depends entirely on how the power supplies are made.
You do not want to hook up the negative side of a negative power supply to the negative edge of a positive power supply if both power supplies are fed from the same place. (You end up accidentally shorting out the negative power supply)
To be sure, it would be a good idea to further describe your circuit and what you are using as a supply.

**Note that ground is often used in situations where there is no post in the earth. This is commonly referred to as Chassis ground and a perfect example of this is in the automotive trade. Please also keep in mind that Chassis Earth may not always be connected to the negative side or 0V side of the power source! Some equipment actually has the Chassis ground wired to the Positive or High side of the power supply.

 

[kpatz]

Can you post a schematic? Where is your 5V and 24V DC coming from?