LED Color Mixer. Evaluation copy. SensorDAQ, LabQuest, or LabQuest Mini. three 220 resistors

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1 LED Color Mixer Project 3 LEDs (Light Emitting Diodes) are long-lasting light sources made from a special semiconductor material that converts electrical current directly into light. Unlike incandescent lamps that emit broad-spectrum white light (all the colors of the rainbow), LEDs emit a small wavelength range that appear as a single color. In the human eye, the receptors that interpret hues of color are called cones. Cones can be classified into three basic types based on their responsiveness to long, medium, and short wavelengths, or red, green, and blue color. A 3-color LED (sometimes called an RGB LED) emits the three colors of light (red, green, and blue) that trigger the cones in the eye. A RGB LED actually contains three individual LEDs encased in one shell. It looks like a single LED with four leads or wires one for each color and a fourth lead for the common ground. Additional colors can be perceived by the human eye when the individual LEDs are illuminated simultaneously in different combinations. PROJECT DESIGN REQUIREMENTS In this Project, you will build a circuit and write a LabVIEW program to illuminate the three different colors of light (red, green, or blue) in a RGB LED. The user should be able to select any one of the three colors by name from a front panel control and be able to turn off all three colors while the program is running. Since LEDs can be destroyed if too much current flows through them, you should wire each of the three leads in series with three current-limiting resistors. MATERIALS SensorDAQ, LabQuest, or LabQuest Mini LabVIEW computer USB cable Vernier Digital Control Unit (DCU) Vernier LabQuest or LabPro power supply Evaluation copy PROJECT SETUP Construct a 3-color RGB LED circuit 1. Connect the 9-pin cable to the side of the DCU. 3-color RGB LED three 220 resistors breadboard jumper wires ping-pong ball Engineering Projects with NI LabVIEW and Vernier Vernier Software & Technology P3-1

2 Project 3 2. Insert the RGB LED and resistors into a breadboard, and then wire the components to the DCU cable as shown in the figure below. You can find the color-coded pin-out for the DCU cable on the label attached to the cord. Tip: There are four leads or wires on a RGB LED. Normally, with a single-color LED you would connect the shorter wire to the ground connection. However, you should not assume that the shortest wire on a RGB LED is the ground wire. Refer to your manufacturer s specifications for the proper wiring connections. Figure 1 Wiring diagram for connecting a RGB LED to the DCU cable Connect the DCU to the interface 1. Connect the DCU to the DIG port on the interface. 2. Connect a power supply to the DCU. 3. Connect the interface to the computer. If you are using a LabQuest, make sure it is turned on. PROJECT BACKGROUND INFORMATION In this Project, you are asked to illuminate each of the three colors (red, green, and blue) in the 3- color RGB LED individually. The Vernier Digital Control Unit (DCU) gives you this functionality. The DCU is an electronic device that allows you to control up to six digital output lines for on/off control of LEDs and other DC electrical components. The DCU connects to the DIG port on the interface and is powered by a separate DC power supply. A 9-pin D-sub socket cable is supplied with the DCU, with bare wires on one end, for use in building projects. There are connections for all six digital lines, plus a power connection and two ground connections. The color code of the wires is identified on a label attached to the cable. Each of the three color leads or wires on the LED should be connected in series with a currentlimiting resistor to the first three DCU lines D1, D2, and D3; the fourth lead should be connected to one of the ground (GND) lines. To illuminate each color, you must send a numeric output pattern to the DCU to turn the digital line on. When you place the Digital Express VI on the block diagram, a configuration window appears. If you select Output Lines 1 6 from the Device Selection tree you will see a picture of the DCU. Change the DCU Pattern values from 0 to 15 for feedback on what lines are activated. As shown in the diagram below, a pattern of 1 will turn on DCU line D1. Please be aware that a pattern of 2 will turn on line D2, but a pattern of 3 will turn on lines D1 and D2 simultaneously. P3-2 Engineering Projects with NI LabVIEW and Vernier

3 LED Color Mixer Figure 2 Configuration window for the Vernier Digital Express VI PROJECT TIPS 1. A diffuser is recommended when using a RGB LED, because the human eye tends to see the individual colors rather than the merged color. A diffuser blends and scatters the three individual light sources making them appear softer and more muted. A ping-pong ball serves as a good diffuser. Cut a small hole through one end of the ball and place it over the lens of the LED. 2. Refer to Appendix E for additional information on the Vernier DCU. PROJECT TROUBLESHOOTING If the third color does not appear to be the appropriate hue, check that you are sending the right value into the Digital Express VI to set the DCU output properly. Engineering Projects with NI LabVIEW and Vernier P3-3

4 Project 3 CHALLENGE DESIGN REQUIREMENTS Note: Do not attempt the Challenge until you have completed the Project Design Requirements. Make four additional colors (magenta, cyan, yellow, and white) with your RGB LED by turning on the three digital lines in pairs or as a triple (refer to the table of DCU output patterns below). Do some initial testing with your LED and your ambient room light to determine which combination of digital lines turns on the four color hues. Modify your LabVIEW program from the Project to allow the user to illuminate one of the seven different colors CHALLENGE BACKGROUND INFORMATION To turn on two or more DCU lines simultaneously, you must send a unique numeric output pattern to the Digital Express VI. The first 12 output patterns correspond to a binary number system. If the switch is in the + position, current will flow and the device connected to that line will be on. If the switch is in the or X position, the device will be turned off. As you can see from the table, sending an output pattern of 7 turns on all three lines. If your circuit is wired properly, turning on all three lines simultaneously should cause the RGB LED to appear white. Output Binary D1 D2 D3 D4 D5 D X X X X X X X X X X X X X X X X Table 1 The digital output patterns for the DCU for use in this Challenge CHALLENGE TROUBLESHOOTING 1. Make sure you are sending the proper output pattern to turn on one or more digital lines. Use the Digital Express VI configuration window to test your pattern and hardware. 2. If you are not getting a good color range in this Challenge, you may need to adjust the value of the resistors in your circuit (they do not have to be identical). The purpose of the resistors is to limit the current through the LEDs to prevent burnout, but they should be sized to give a good range of adjustment on each color. Check the manufacturer s data sheet to find the typical operating current for your particular LED. You can tell you have good color balance if white light is produced when all three colors are illuminated. P3-4 Engineering Projects with NI LabVIEW and Vernier

5 EXTREME CHALLENGE (SENSORDAQ ONLY) LED Color Mixer Produce even more color hues by varying the intensity or brightness of one color s illumination using a concept called pulse-width modulation. Pulse-width modulated signals flash the LED on and off at a high enough rate of speed as to be perceived as a solid color by the human eye. The color s intensity is controlled by the fraction of time the color is on (commonly called the duty cycle). Using blue as the base color and red as the modulated color, write a LabVIEW program to produce color hues from blue to magenta (the combination of blue and red). The duty cycle for the red LED should be controlled independently from the front panel. Note: The Extreme Challenge is not possible with the LabQuest or LabQuest Mini due to the lack of a pulse generator on these interfaces. EXTREME CHALLENGE BACKGROUND INFORMATION In the Extreme Challenge, you are asked to build a Color Mixer that will display a continuous range of color hues. Having two colors on simultaneously will produce a new color, but you will get a much broader spectrum of color if you vary the intensity of one color as well. By flashing one LED on and off at various duty cycles, while keeping the other LED on all the time, you can create a range of shades between the two LEDs. The SensorDAQ has the capability to send output pulses from the DCU line D1. You can control the pulses with a technique called pulse-width modulation (PWM). In any one pulse, PWM limits the amount of time a signal is on. The ratio of on time to total time is called the duty cycle. In the pulse train shown below, the pulse is on for 60% of the time and off for 40% of the time. Figure 3 Pulse-width modulated signal When using PWM at very low frequencies with an LED, there is a noticeable flicker in the light as it is switched on and off; but once you get above the flicker frequency of the human eye, the light appears as a single, continuous color. This allows you to control the intensity, or brightness, of the LED by varying the duty cycle. Engineering Projects with NI LabVIEW and Vernier P3-5

6 Project 3 Since you are blending colors, you will have one LED on continuously, while varying the intensity of a second LED with a PWM signal. For example, if the blue LED is on continuously while the intensity of the red LED is varied, the colors you observe will range from blue to magenta (the combination of blue and red). Figure 4 Color mixing with pulse-width modulation Fortunately, the SensorDAQ Digital Express VI has a Pulse-Train Generation selection that can be used to control an LED with pulse-width modulation. When using the pulse generator, the LED to be varied must be connected to DCU line D1. Due to hardware limitations, pulses cannot be sent from any other DCU lines. The LED that will remain on continuously should be connected to DCU line D3 or D4, but not DCU line D2, D5 or D6 (when the pulse generator is active, these lines are not available). Keeping one LED on continuously and sending a pulse train to a second LED requires you to use two Digital Express VIs. Referring back to Table 1 and the example shown above in Figure 4, if the red LED is connected to DCU line D1 and the blue LED is connected to DCU line D3, you would use one Digital Express VI to turn on the blue LED and a second Digital Express VI to send a variable pulse to the red LED. EXTREME CHALLENGE TIPS 1. Set the Frequency on the pulse generator to 50 Hz. 2. The Duty Cycle is a decimal number between 0 and 1, but you should avoid sending an actual 0 or 1 to the Digital Express VI as these values are not supported. P3-6 Engineering Projects with NI LabVIEW and Vernier

7 Vernier Lab Safety Instructions Disclaimer THIS IS AN EVALUATION COPY OF THE VERNIER STUDENT LAB. This copy does not include: Safety information Essential instructor background information Directions for preparing solutions Important tips for successfully doing these labs The complete Engineering Projects with NI LabVIEW and Vernier manual includes 12 projects as well as essential teacher information. The full lab book is available for purchase at: Vernier Software & Technology S.W. Millikan Way Beaverton, OR Toll Free (888) (503) FAX (503)