Maker Pro
Maker Pro

whats the difference between 1 terminal power and 2 terminal power in falstad?

Martaine2005

May 12, 2015
4,957
Joined
May 12, 2015
Messages
4,957
“It seems to behave differently”.
Yep, 1 terminal connection doesn’t work and TWO connections does work!.
Forget the simulator and try it!.

Martin
 

dragon

Oct 31, 2022
248
Joined
Oct 31, 2022
Messages
248
I think I know what it is I'm thinking of.

If you look at the problem pneumatically, You could think of 2 terminal power being a through pump, and 1 terminal power being a pump in from outside or an exhaust to outside.

If you want to implement that with a 2 terminal device, you pretend the ground is inbetween positive and negative, and then you can have as many +5v's as u want, and as many exhausts as you want.

But it behaves differently than if you had a heap of 2 terminals in the circuit together, because they conduct through, and 1 terminals conduct in and out, so its different.
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,767
Joined
Nov 17, 2011
Messages
13,767
If you want to implement that with a 2 terminal device, you pretend the ground is inbetween positive and negative, and then you can have as many +5v's as u want, and as many exhausts as you want.
No.
"ground" is a more or less arbitrary designation for a reference potential to which voltages are refenreced in a circuit. Typically ground is 0 V, although this is not necessarily so (sorry to confuse you), this is only by definition or call it common understanding among electronics designers/engineers.
In the case of a single battery, you typically connect ground to the negative terminal of the battery and then the other terminal will be positive with respect to ground.
When you use multiple batteries (or power sources), you can connect the batteries in various ways. Here's an example:

1679563735422.png1679563915256.png1679563939115.png

In the left example you have +5 V from the lower battery and on top of that another 5 V from the top battery, making for 10 V from the top to ground.
In the middle example the batteries are connected just the same, but ground has been connected to the center. Both batteries deliver 5 V, which makes + 5 V from the top to ground and -5 V from the bottom to ground.
In the right example the batteries again are connected the same way, but ground has been moved to the top. Now the top battery delibers -5 V with respext to ground, teh lower battery adds anoterh -5 V so the bottom battery terminal is at -10 V with respect to ground.

As you can see, the same connection allows different voltages with respect to ground depending on where you place ground. Rememeber that wehre you place ground is more or less arbitrarily, but PLEASE don't use this to place ground just anywhere to confuse us. Follow conventions and connect it to the negative of the battery (or in the center, if required).

If you look at the problem pneumatically, You could think of 2 terminal power being a through pump, and 1 terminal power being a pump in from outside or an exhaust to outside.
Picking up on this example: The pump from the outside also has an "invisible" connection (2nd terminal) to the other end. The air pumped out one end of the pump (exhaust) eventually goes back to the other end (input) vis the free air circulating between the room and the outside. The free air acts as an "invisible" tube just like the ground connection not being shown in the 1-terminal battery example. You can't see it, but the connection is there.
 

dragon

Oct 31, 2022
248
Joined
Oct 31, 2022
Messages
248
This "imaginary ground" or "theoretical ground" I never liked it, because a real ground. (which is a hole in the pipe if its pneumatic) is more important cause its actually in the functioning of the machine.

Having a source of 0v will make a ground electrically, but i'm yet to put that into the sim yet. (I dont know how to do it.)
Maybe u connect it to both negative and positive, but I dont think itll like u doing that, that much, but I think its a short of some kind.
 
Last edited:

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,767
Joined
Nov 17, 2011
Messages
13,767
This "imaginary ground" or "theoretical ground" I never liked it, because a real ground. (which is a hole in the pipe if its pneumatic) is more important cause its actually in the functioning of the machine.
In reality there will always be a real ground.
Having a source of 0v will make a ground electrically,
You haven't grasped the concept of voltage or voltage sources. A voltage is always teh difference in potential between two point in a circuit. There is no such thing as a single point having a voltage. A voltage source of 0 V is still a circuit having two points only with a voltage of 0 V between the two points. Consequently there is no use in adding a 0 V voltage source to connect to ground.

Maybe u connect it to both negative and positive, but I dont think itll like u doing that, that much, but I think its a short of some kind.
Definitely a short circuit -> bad idea.
In post #24 I have given you 3 different ways to connect ground (there are still a lot more possibilities). As long as you stick to falstad it seems that you don't have to worry about connecting ground as falstad obvioulsy works without having an explicit ground.
Stick to 2-terminal voltage sources and draw allconnections as required. Then you will not have to deal with "imaginary" connections.
 

dragon

Oct 31, 2022
248
Joined
Oct 31, 2022
Messages
248
Falstad has grounds in it, I use them. But how do you actually make a ground in a real circuit?
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,767
Joined
Nov 17, 2011
Messages
13,767
But how do you actually make a ground in a real circuit?
Bury a hole in the earth, put a long copper rod in it, fill the hole.

No, of course not. That would be an Earth connection.

"ground" is an arbitrary name for a common reference potential. As with all other potentials you use wires to connect the components. You name the wires with (hopefully) meaningful names like Vcc, SIgnal_in, Signal_out, ... And one wire is named "ground". There is nothing special in the physical construction of "ground". It is just a name for the wire that is on reference potential.

There are aspects to a "ground" that are worth special consideration, especially once frequencies above a few Hz are involved, but these are imho currently way above your level of understanding. For the time being try to understand basic electronic circuitry with "ground" being just a signal name.
 

dragon

Oct 31, 2022
248
Joined
Oct 31, 2022
Messages
248
I think I figured it out!!! if you have one battery for the pump in, and one battery for the pump out, then the ground is the wire connecting them at the back!! 0 volts!!!
 

Martaine2005

May 12, 2015
4,957
Joined
May 12, 2015
Messages
4,957
You don’t need two batteries.
One battery has a voltage between the two terminals. It is positive and negative. Negative being the 0V.
1679580090050.jpeg
 

dragon

Oct 31, 2022
248
Joined
Oct 31, 2022
Messages
248
The earth component/terminal in falstad, is 0 volts, its not 2.5 volts, or any other volts. a REAL earth is only ever 0 volts. But u are right, I understand now that halfway volts will act just like an earth anyway, next to the other appropriate voltages.

Its a pumpless escape to the atmosphere, an exhaust, is 0 volts. or in real life gas-flow style, 1 bar.
 
Top