10 LED Projects for Geeks: Build Light-Up Costumes, Sci-Fi Gadgets, and Other Clever Inventions

10 LED Projects for Geeks: Build Light-Up Costumes, Sci-Fi Gadgets, and Other Clever Inventions — page 9 — These figures show the digitally controlled RGB LEDs in a variety of packages including tiny surface-mount chips four-pin through hole packages LEDs attached to little circuit boards and even LEDs preattached in flexible grids A final type of RGB LED is a two-connection internally controlled LED These are a good option if you’re looking for really cheap RGB LEDs with only two leads These LEDs have a small control chip inside but unlike with the digitally controlled RGB LEDs you can’t actually control what they do For example as soon as you provide power to these LEDs the internal control chip starts displaying a prerecorded sequence of colors on the RGB LED usually cycling through each primary and secondary color with a nice color fade between each one reading an lED Datasheet The manufacturer of any LED usually provides a technical datasheet full of facts and figures It can seem overwhelming but don’t worry For the purposes of this book you need to know only two important numbers to use the LED safely Figure 6 shows a typical LED data sheet that you’ll use to find the critical details which are highlighted here in red Figure 6 An LED datasheet with forward current and forward voltage highlighted in red 7 i n t rO d u c t i O n

10 LED Projects for Geeks: Build Light-Up Costumes, Sci-Fi Gadgets, and Other Clever Inventions — page 10 — An LED produces light when electrical current flows through it but too much current can overheat and damage it Using the forward voltage and the maximum current parameters from the datasheet we can figure out what size resistor we need to operate the LED safely forward Voltage The forward voltage or Vf of an LED is the minimum amount of voltage the LED needs to start conducting electricity It measures the difference in voltage between the anode and cathode when it’s on If you apply a voltage below Vf the LED will not conduct any electricity or light up When the LED is operating normally the voltage across the LED will be equal to Vf We’ll use this fact later on when we start calculating circuit parameters The Vf of an LED depends on the chemistry of the materials used which also determines the color of the LED For example red LEDs have a typical Vf of 1 5 to 2 V while blue or white LEDs tend to have higher Vf values in the range of 2 to 3 V Maximum Current If your voltage exceeds Vf the LED conducts as much electricity as possible which can overheat and damage it To prevent this we need a second value from the datasheet the maximum current which is the maximum electrical current that can pass through the LED without overheating it Most LEDs have a maximum steady current and a higher maxi mum pulsed current Usually we use the maximum steady current for our calculations We measure current in units of amperes or amps abbreviated as A and in thousandths of an amp or milliamps abbreviated as mA Current is the amount of electricity that is flow ing through a device and it determines the brightness of an LED For example most small LEDs light up with only 10 to 30 mA of current Some larger LEDs and LED assemblies need hundreds of milliamps or even several amps of current resistance lEDs and ohm’s law To safely power an LED we need to provide at least Vf voltage across the LED but also limit the current to ensure it remains below the data sheet’s max current allowed The easiest way to do this is to add a resistor in series inline with the LED A resistor is the simplest pos sible circuit component with a very simple relationship between the 8 i n t rO d u c t i O n

JavaScript Required

Whoops! We're sorry but Epic doesn't work properly without JavaScript enabled. Check your web browser's settings to make sure it's enabled.