## Is the term ground correct?

JurgenRoman
Posts: 33
Joined: Mon Aug 24, 2015 7:43 am

### Is the term ground correct?

I'm writing a highschool thesis on communication and a project we made with a raspberry pi.
We connected a relay to a raspberry pi and can controll it from our phone. The relay we use has to be connected to a 5v pin and a ground.

Now is my question:
Is the term ground correct? Because if the current flows from the 5v pin to the relay, it would need to return somewhere too, is this to the ground pin? Because if that is the case, the term ground wouldn't be correct?

A ground should be to avoid static electricity?

i have connected the 2 using female female jumper wires
relaygpioimage.png (7.77 KiB) Viewed 720 times

W. H. Heydt
Posts: 11097
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

### Re: Is the term ground correct?

Yes....ground is another way talking about the negative/zero voltage terminal. While we speak of current flowing from positive (+5v in this case) to negative or ground (0v), in point of fact, the electrons actually move the other way. Blame it all on Benjamin Franklin for having two possible choices and picking the wrong one. (Don't blame him *too* much, though, he had no way to know.)

Edit to add... Find a source of electrical and electronic circuit symbols. Learn the ones you need and slowly expand that list. Draw your circuits using standard symbols so that anyone can read and understand your circuit...and so can you a few years later.
Last edited by W. H. Heydt on Tue Dec 08, 2015 10:15 pm, edited 1 time in total.

drgeoff
Posts: 9925
Joined: Wed Jan 25, 2012 6:39 pm

### Re: Is the term ground correct?

The current returns to the other terminal of the power supply.

All voltages are potential differences, that is they are between two points. It is convention that one of them is called ground or earth even though it may not actually be at the same potential as the Earth (the planet, hence the capital E).

JurgenRoman
Posts: 33
Joined: Mon Aug 24, 2015 7:43 am

### Re: Is the term ground correct?

drgeoff wrote:The current returns to the other terminal of the power supply.

All voltages are potential differences, that is they are between two points. It is convention that one of them is called ground or earth even though it may not actually be at the same potential as the Earth (the planet, hence the capital E).
Thanks! That was the confusion, cuz i didn't know if it had the same potential as the earth

JurgenRoman
Posts: 33
Joined: Mon Aug 24, 2015 7:43 am

### Re: Is the term ground correct?

W. H. Heydt wrote:Yes....ground is another way talking about the negative/zero voltage terminal. While we speak of current flowing from positive (+5v in this case) to negative or ground (0v), in point of fact, the electrons actually move the other way. Blame it all on Benjamin Franklin for having two possible choices and picking the wrong one. (Don't blame him *too* much, though, he had no way to know.)

Edit to add... Find a source of electrical and electronic circuit symbols. Learn the ones you need and slowly expand that list. Draw your circuits using standard symbols so that anyone can read and understand your circuit...and so can you a few years later.

I just really quickly made an image in paint

rurwin
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Contact: Website

### Re: Is the term ground correct?

The actual circuit is a bit more complex than what you are thinking of, which might be causing your confusion.

The GPIO output is too weak to drive any relay that I have ever found, so it needs to be amplified first. The relay board that you are using probably has another chip on there to do that. It's probably a darlington pair, just a pair of transistors tied together, but if your teacher hasn't told you that then you don't need to know the details.

The current comes out of the GPIO, through the darlington pair and to ground. At the same time another current comes out of the 5V, though the relay and the darlington pair to ground. The darlington pair switches that current on and off depending on whether it is getting a current from the GPIO.
Relay board currents.png (31.47 KiB) Viewed 586 times