After building a few circuits you should start to see that LED brightness can be controlled by altering the size (resistance) of the current limiting resistor used in the circuit.
LED Brightness and Current Flow
We know from Ohm’s law (V=IR) that for a fixed voltage (5v in case of an Arduino digital pin) current is inversely proportional to resistance.
What does that mean?
If we hold voltage constant:
– increases in resistance will reduce current.
– decreases in resistance will increase current.
LED brightness is proportional to current — so small resistors give bright LEDs and big resistors give dim LEDs.
Note if resistance gets too small, you will have dead LEDs not bright ones — see why here.
Let’s build some circuits to explore this relationship.
Required Parts
- breadboard
- battery pack
- wire battery clip
- leds (single color all the same)
- resistors — fixed several
- Ohm’s law chart
Video
UPDATE FOR 2023:
In the following video I use a battery pack to provide power (we will look at batteries soon). Remember circuits have two complimentary halves: the source side and the sink side. You can work through this video with an Arduino for power instead of battery power. The build will follow a parallel path after you have your power source setup.
One big difference is that a battery pack provides 9V — instead of 5V. You can imagine this as a tall vs short waterfall (charge difference). So in the video i talk about 9V — where, if powered from Arduino, you will only have 5V. The principles discussed remain the same.
GETTING SET UP: To use your Arduino for power, set up the power side of your circuit like the image below — the action on the breadboard does not change. At this stage dupont wires are your friends — use red and black if you have them — or others colors that are available. (Remember you need to connect your Arduino to a plugged in USB cable — not shown — so that the Arduino has power!).
In the image above the red wire is connected to 5V from the Arduino and the top red rail on the breadboard. The black wire is connected to Arduino Ground and the blue rail on the bottom of the breadboard.
With that completed you are ready to watch the video!