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I'm learning from zero background taking a course in basic electronics. I did the math. But the circuit here won't simulate at all without a ground, and then the values are not as calculated: the current is negative, and there is no V across the second R, I guess because of the ground. https://www.circuitlab.com/circuit/ku7bhr/l3-proj-1/

I assume this is just an artifact of the simulator that I need to work around. Any advice for how to think about this would be welcome.

I find reading the documentation for any new tool can often be quite helpful:

https://www.circuitlab.com/docs/

in particular:

https://www.circuitlab.com/docs/the-basics/#ground

Something that is not explained in CL is that the indicated direction of current flow in a component (i.e. a resistor) is with respect to the ends of that component (in the case of a resistor Rx the pins will be called: Rx.nA and Rx.nB).

So if you place a resistor and blindly stick a probe on one end without noting which end it is, you may get a +ve or a -ve current flow indicated.

There are 3 simple ways to avoid this:

i) take care when placing components to note which end is which (hover the mouse over the pins until a grey blob appears that will then show you in the bottom right of the window info about the pin);

ii) Same as (i) but always orient your components the "right" way round then when you probe the positive ends of components, you'll see positive currents;

or:

iii) Use the CL Ammeter (and then, just like a real Ammeter, take care about which way round you connect it).

For beginners, (iii) is probably the best option.

More about wires and nodes

If you hover your mouse over the end of a lead of a component that you have placed on the schematic a large, light grey dot will appear right at the end of the wire.

That is the (only valid) connection point for that component lead. Also referred to as a Node:

https://www.circuitlab.com/docs/the-basics/#nodes

If you Left-click and hold on that grey dot then drag the mouse cursor, a wire will appear.

Drag it to the next node you wish to join.

If you need to turn a corner, let go and then repeat the process on the node dot at the end of the wire you have just drawn and drag at right angles.

Note that you can also join nodes just by attaching a label to a node and then attaching a new label with the same name to another node. Those two nodes are now connected exactly as if you has drawn a wire between them:

https://www.circuitlab.com/docs/the-basics/#named_nodes

You can also draw a wire by clicking on the "Wire" button on the left hand palette then left-click and drag and release on the schematic.

To repeat a placement press shift before you click on the component you wish to place.

However, you must be consistent in your labelling:

https://www.circuitlab.com/forums/support/topic/86m9393x/bug-report-inconsistency-in-using-net-label-as-a-voltage/

Note also that CL assigns arbitrary but sequential node names to unlabelled nodes.

This can lead to very confusing results where node names are used in expressions for arbitrary sources and plot expressions.

Suppose you have a circuit with 17 nodes then you replace a resistor with a piece of wire.

Your circuit now has only 16 nodes. Suppose the node you removed was Node17.

Suppose you then add a new component in a different location that then adds a new node (by inserting a resistor in a wire for example). The new node will be auto-labelled by CL as Node17.

If you now add the first resistor back in it's original location. The node that reappears will now be auto-labelled Node18 and not Node17 as it was originally.

More complex editing makes a more comprehensive mess of the CL assigned node names.

If you put node name labels on all the nodes you are interested in then they won't change numbering or flicker in and out of existence as you edit your circuit. They will then always be valid in your expressions.

You can set up explicit voltage sources for the power supplies in CL or create an implicit supply using a node or net name. For example, the +1V or +1 node label invokes an implicit 1V source:

https://www.circuitlab.com/circuit/a5bzf7/good-netname-and-a-free-voltage-source/

However, in:

https://www.circuitlab.com/circuit/96br67/bad-net-name/

CL throws an error because the explicit 1V source, V1, is then in parallel with the implied source created by the node label.

:)

Great response, Signality. I'll print and read and try. Just at the beginning I see hidden properties being revealed. Thanks! Michael

:)

You might like to note that the CL battery includes a series resistance. It's not an ideal (zero resistance) voltage source - like the CL > Ideal Sources > Voltage Source - which is why V(R1.nA) is not exactly 6V.

Having said you need to refer to the CL documentation, as you may already have guessed, there's a lot of CL that is not well documented so you need to look carefully at the parameters of all the CL components as you use them.

Questions? Just ask!

Thanks Signality. I'll try the Ideal Source. The documentation at least tells me about the ground, but leaves a lot to be desired. I'm glad for your help. I will definitely get back to you with more on this circuit before I move on to more complicated ones.