Intro to LED Strips




LED strips are a very fun and effective way to give lots of glow and color to a project. In this Instructable you will learn about the basic kinds of strips and how to hook them up to the Intel Edison with Arduino breakout board. These circuits include hardware needed for external power and how to set up a button and potentiometer to blink and fade using Intel’s special flavor of Eclipse IDE and their LPD8806 library.

Step 1: Analog

There are two basic kinds of LED strips, analog and digital. They are controlled differently, so it’s good to know which one you need for your project.




Analog strips come in mono (one color) or RGB (full color spectrum). They are sold on reels and can be cut into small segments. The segments are marked by metal contact pads and sometimes have a scissors icon screen printed right on them (love those!). The strips shown here are segmented in 5cm and 10cm lengths, each segment containing 3 LEDs. Usually strips use 30, 32, 60 or 120 LEDs per meter, which will change price and power consumption.

For each segment the LEDs are wired in series, which means the operating voltages are added up, giving the higher voltage needed. All of the segments are wired in parallel, so they get all get the same amount of voltage all the way down the strip, but the current draw adds up depending on the length of the strip. For more information on how to power your strip, skip to step 3.

Behavior

The LEDs that fade and blink together, stay together. All the LEDs on the strip will act as one, they are non-addressable. One way to tell by sight is that they do not have any driver chips that you can see on the strip (that would be digital!).

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Step 2: Digital

Digital strips come with RGB LEDs and have a driver chip on the strip that control the LEDs individually. These are also called individually addressable or just addressable.

Shown here is a strip using the LPD8806 driver. Other popular ones you will see are using the WS2801 driver and strips using WS2812 RGB LEDs, which have the drivers build right in the LED package! They too come segmented, where they can be cut down to bite-size lengths.

These strips take 5 volts, so they can run straight off a microcontroller. They will power up when attached to 3.3 volts, just not as bright.

You will want to use a microcontroller with these to program cool patterns and make them reactive to sensors and switches. Most of the work is in the software, the hardware set up is simple and will be gone over in a later step. Digital strips get their information from one data-in pin or two data-in and clock-in pins, dependent of what strip is used. Make sure to check the datasheet for the pinout diagram, voltage ratings and other useful information.

Behavior

The neat thing about addressable strips is that each LED can do it’s own thing. It can be any color it wants at any time. The makes blinking patterns and color swirls possible, and so much more.

Step 3: Power

To keep your LED strip project glowing brightly with the appropriate power, you will need to know how much current your project draws and it’s operating voltage. Once you know those two things, you can choose a power supply. Keep in mind that current draw can be a tricky thing to figure out. Here we will take information from the datasheet and plug it into some simple equations to get the max current needed, since the information from the datasheet are if the LED is on at full brightness.

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To calculate the needed power supply, we will need the following info:

  • length of strip
  • number of LEDS per meter
  • current draw per LED OR power consumption per LED
  • operating voltage

LED strips are commonly powered on 5V, 12V and 24V. The number of LEDs per meter (lpm) factors in the power calculation as well. Strips can be 30, 32, 60, 144 or more per meter.

Using Current Draw Per LED

As an example let’s look at the white strip’s datasheet. We can see the operating voltage is 12V, which should also be screen printed on the strip itself at the cut line of each segment. What we are looking for is the current draw measured in milliamps (mA). It tells us that each segment made up of 3 LEDs draws 60 mA. To make the calculations easier, the current draw can be divided by 3 totaling 20mA per LED. If one meter is being used with 60 LEDs per meter we have this information:

  • length of strip = 1 meter
  • number of LEDS per meter = 60
  • current draw per LED = 20 mA

Equation:

(Length of LED Strip x LEDs per Metre x LED current draw)

Plug in info:

1 (meter) x 60 (lpm) x 20 mA = 1,200 mA

1,200 mA / 1,000 = 1.2 amps.

Using Power Consumption Per LED

Another way of calculating current draw is using the power consumption per LED. The power consumption can also be used to find current draw if the power consumption, measured in watts per LED is known instead. The datasheet tells us .72 watts for 3 LEDs. First divide .72/3 = .24 watts per led

  • length of strip = 1 meter
  • number of LEDS per meter = 60
  • power consumption per LED = .24 watts
  • operating voltage = 12V
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Equation:

(Length of LED Strip x LEDs per Meter x LED Power) / 12

Plug in info:

(1 x 60 x .24) / 12 = 1.2

We now know that we want to use a a power supply that can provide 1.2 amps and 12 volts. Keep in mind that the current draw per LED is at full brightness. If the strips are dimmed through a PWM pin on the Edison, it will take less current. Going by the max amount is still a good guide to know if you have enough to begin with.

Battery Life

Battery life is based on current draw of, again it will fluctuate, especially with the digital RGB strips when patterns and colors are dancing along it. Current draw will fluctuate dependent on the color and brightness the LED is outputting. The way to accurately get the current draw is to hook it up to a multimeter and watch the amps change per pattern cycle, take note and do some calculations.

Another way to find out battery life with a dynamic project, hook up a battery at full strength and see how long it takes to drain.

This aside a general calculation can be made by looking at a batteries mAh rating. Let’s stick with the white strip, 6 AA batteries are being used to power the example circuit. AAs roughly have 1500mAh, the 8 batteries are in series so the current stays the same at 1.5 amps. Divide this with the current draw of our project, which is 1.2.

1500 mah/1.2 amps = 1.25 hours of full brightness

Read more: Intro to LED Strips




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