Understanding Protoboard Circuits: How Do Ground Connections Work?

[bmxicle]

Homework Statement

Sorry if this is in the wrong forum, but it is for an introductory lab course.

I am trying to set up the simple circuit in part A of my drawing on a protoboard containing the components in part B of my drawing.

Homework Equations

n/a

The Attempt at a Solution

The protoboard has these single cable connections for the ammeter, voltmeter, function generator etc, and then a standard breadboard as (poorly) depicted by the picture in part B. The rows of five are all electrically connected like in a standard breadboard. There are also positive pinslots for a wire to come out at the attachments for the function generator etc.

I have no experience wiring circuits where the grounds are all just implicitly connected together like they are on this one so I'm having a hard time visualizing how the circuit goes on the protoboard.

So I'm just checking if the way i have drawn the wires/resistors/function generator etc on the protoboard in part B, is the same as the circuit in part A, and any tips on understanding how the grounds are interacting in the circuit would be of great help.

Sorry in advance for the messy drawing :p

 

[lewando]

You have left out the ammeter. There should be a node shared by the resistor, voltmeter and ammeter.

 

[bmxicle]

Isn't the ammeter connected right at the negative 'end' by the grounds though?

 

[lewando]

One side of the ammeter is connected to ground in figure B, the the other side is not. Therefore, it is not doing much of anything. You are showing the resistor connected to ground in figure B. This is not how it should be hooked up according to figure A (it should be connected to the positive terminal of the ammeter).

Another thing to consider is your voltmeter seems to be connected to ground in figure B, this is not how it should be hooked up according to figure A (it should also be connected to the positive terminal of the ammeter).

 

[bmxicle]

You mean like in the picture i drew below? Doesn't that put the ammeter + resistor in parallel with the voltmeter?

 

[lewando]

Not really. There should only be two things attached to ground-- your function generator (bottom or negative terminal) and the ammeter (bottom or negative terminal).

[edit] Can you take a picture of your breadboard? Are the three devices: function generator, voltmeter and ammeter constrained to have all three negative terminals grounded as you have sown in original figure B (I hope not)? Or are they just 2-terminal plug-in points (probably the case)?

 

[bmxicle]

I was under the impression that since that the voltmeter, ammeter and function generator all connect with a single cable (which contains the positive lead inside, and the negative lead or ground on the outer metal jacket of the cable) to the protoboard unit that each object has a separate ground point at the start of the circuit. Is that wrong? I'm having a hard time seeing how to connect the voltmeter without it being grounded also.

I feel like I'm missing something very simple.

 

[lewando]

I mean, does your actual breadboard look like this:

 

[bmxicle]

No it doesn't. Here is a picture of the actual protoboard, sorry it isn't closer

 

[bmxicle]

On the diagram you drew I could construct the circuit fine because there are clear positive and negative terminals for each item, but I can't see those on the protoboard I'm using.

 

[lewando]

Yes, I see--good image. The voltmeter definitely does not need to be grounded per your original figure A. Are you constrained to connect the voltmeter to your circuit via one of those BNC connectors? Can you improvise a direct connection of the voltmeter across the resistor.

 

[lewando]

A thought just occurred. Since the voltage drop across the ammeter should really be very small, you might be able to neglect it and use a voltmeter connected to ground. If so, your figure A should change to reflect that.

 

[bmxicle]

I think we are supposed to construct the circuit using the BNC connectors, and our TA suggested we connect the voltmeter in that fashion so It can be done. I don't even think we were provided with cables to form a direct connection across the resistor with the voltmeter. I may be able to find some cables to just connect the voltmeter across the resistor directly, but I'm still curious as to how you would create that circuit without one of those cables.

 

[bmxicle]

Yeah that makes sense, in that case would the second drawing I made with the three ground connections represent the circuit you're talking about?

 

[lewando]

I'm curious too. Discuss with your TA if you can. I need to sign off now. Update your post, I'd like to see you get this working.

 

[lewando]

Yeah that makes sense, in that case would the second drawing I made with the three ground connections represent the circuit you're talking about?

Yes.

 

[bmxicle]

Thanks for your help, I'm going to stop by the lab tomorrow and play around with the circuit so I'll post after that.

 

[bmxicle]

Well I went into the lab, and now that I have a better understanding of how the ground connections work I found several other ground connections on the other end of the protoboard so it became pretty straight forward to set up several things in parallel with the coaxial cables. I knew it had to be something really simple that I was missing, thanks a lot for your help though.