How do I use Circuit Lab to show me Voltage and current information on this circuit?

Question

I have a bunch of red LEDs, I don't have their data sheet and I am trying to figure out a safe resistor to use to lower the current across them safely.

My current setup is as follows:

^{simulate this circuit – Schematic created using CircuitLab}

I figured a 100 Ohm resistor and 68 ohm resistor in series because, assuming a forward voltage of the led of 3 volts, and a desired current of 20mA (which I assume is ok?) I get:

R=V/I
R=3.3/0.02
R=165 Ohms.

So, I pop that into the circuit lab as shown below, click run, then click DC simulation, but then it just throws an error saying : "unable to get solution"

How do I use this tool to allow me to inspect various values at various points in the circuit? Have I got this wrong somehow?!

Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Add a GND to the schematic so the simulator has a zero volt reference.

Figure 2. Add nodes at the points you want to monitor. Rename them to suit your purposes. Run the DC solver.

Figure 3. Click each named node to add it to the DC solver tab.

Figure 4. Click on a wire to monitor the current.

Answer 2

If 6.3V is stable, you can use AlInGaAs RED LED x3 in series with NO resistors safely.

Then use as many 3S strings in parallel as your regulated PS can support.

If Vout is 6.5 or more then add 1Ohm per 100mV per 100mA of LED current. imagine each 5mm Red LED as a 1.8V diode with 15 Ohms inside, give or take xx%

• edit (typo , 1.8 not 2.8)

• To answer your (explicit) question for single point voltages, add gnd , which will work, then to see current, select component by name.
• for better help on volt/amp meter readings read https://www.circuitlab.com/docs/the-basics/#volt_and_ammeter