Transistor controlling LED brightness

That's the basic idea, if you put a trend up, you can see what is happening and choose the resistors a bit closer. http://everycircuit.com/circuit/4530947003514880

BillyT I don't know what you mean by a trend

He meant to say trim. Aka pontentiometer.

I touched on the resistor then touched on the eye on the bottom bar. The trend line then appeared on the display above the circuit. The trend line in this case is mA. As you are making adjustments to the circuit, you can see how they are affecting the circuit. This way you are able to tell if the adjustment you are making is working towards what you are trying to achieve or not.

Could it be possible if you could change this circuit around to demonstrate what you are saying? I wouldn't mind a bit.

Sorry I am new to this. I think I know what you are saying.

Ok, we will look at you circuit. I notice that there is now a trend line and the led resistor is now 500 Ohms to increase the maximum led current closer to the 20mA point, checking with ElectroDroid we find that the common value of resistors in that region either a 510 or 470 Ohms device, the 470 Ohm resistor gives slightly more than 20mA so use that one. Now adjust the potentiometer while watching the trend line, the led current reaches 20mA when the potentiometer is about 40%. The potentiometer still has 40k to go, let's add that 40k to the 10k resistor above the potentiometer, remember 51k is a common value. Now adjust the potentiometer, going from 0% to 100% will now adjust the led current from 0mA to 100mA. This is a basic way of using the trend line to show you what is happening in a circuit, and it enables you to achieve the desired output of the circuit you are designing. I hope that this helps to understand the power and ability of EC's design.

You can touch some circuit components and see the current flowing through them, a line can be trended to show the voltage at that point with respect to the circuit ground, to see what the voltage between two points is , connect a voltmeter to them and trend it. Trends will make your circuit designing a lot easier.

Thanks BillyT