0.1 Ir remote control lab

Ir remote control using national instruments low cost data acquisition

Introduction

Have you ever wondered how a typical remote control works? When the user presses a button on the remote, aninfrared signal is transmitted across the room and detected by a sensor called a photodetector. You will create a remote control ofyour own in this exercise.

In this lab, you will use a standard universal remote control to transmit an infrared signalseveral feet. A detection circuit will then be constructed using a specific type of photoreceiver known as a photodiode. Next, a Low Cost USB DAQ device will be used to digitize the infrared signal. Finally, this digitized signal will be analyzed using LabVIEWsoftware to control the popular iTunes application with the help of ActiveX controls.

Pre-lab assignment

1) Why can’t humans see the infrared light coming out of a remote control? Look online or in a textbook tofind the wavelengths of the visible light spectrum as well as the wavelengths of the infrared light spectrum.

2) Write a short summary about how the photodiode works. You should be able to find a variety of sourcesonline; cite them in your response.

3) Search Google for “infrared photodiode datasheet” and see what you can find. What specifications arecommon for photodiodes? Verify that the photodiode detection range is within the infrared spectrum.

4) To generate the infrared signal, your remote control contains an infrared LED. Find an infrared LEDdatasheet online. What specifications do you see? Verify that the infrared LED emission range is within the infrared spectrum.

5) Become familiar with the National Instruments USB 6008 and 6009 data acquisition devices. Thesedatasheets are available at www.ni.com .

Theory

Infrared signals are very similar to visible light, except they occupy a section of the electromagnetic spectrumthat makes them invisible to the human eye. In scientific terms, the infrared spectrum contains wavelengths ranging fromapproximately 1.0 mm to 0.7 um. It is convenient to use infrared signals for remote control transmission, because their reception isnot strongly affected by the amount of ambient light present at the photodetector.

One common method of converting an infrared remote control signal (0.7 – 0.9 um wavelength) into an electricalsignal is using an infrared photodiode. In addition, another method is using a phototransistor. For this laboratory exercise, we willfocus on an infrared photodiode transducer similar to the one shown below:

When used in a circuit, the photodiode will be reverse biased and, as with an ordinary diode, no current willflow. However, any incident infrared light will cause electron-hole pairs to form in the photodiode semiconductor, and thus a currentwill flow. In this way, an infrared signal can be converted to an electrical one.

Hardware and software required

• Infrared photodiode
• 100 kOhm resistor
• Remote control (any infrared device should work)
• National Instruments Low Cost USB DAQ
• LabVIEW 8.20 software (LabVIEW 8.0 will work as well)
• iTunes software

Laboratory exercise

In this exercise, infrared data will be acquired from a photodiode and then digitized using a Low Cost USB DAQ device. Once the infrared signal exceeds a given threshold (meaning that a remote control button is beingpressed), LabVIEW will send an ActiveX command to make iTunes play a song. Holding down a remote control button will result in iTunesskipping to the next song in the current playlist. When finished, the LabVIEW front panel will resemble the following:

1) Connect the following circuit to the Low Cost USB DAQ as shown. The photodiode can be purchased cheaply atRadio Shack, etc. Note that the +5V power supply can be obtained directly from the National Instruments USB 6008 or 6009devices.

2) Using the DAQ Assistant and Acquire Sound Express VIs, create the following LabVIEW block diagram. Note thatthe false case of the outer case structure simply passes through the ActiveX automation refnum.

3) Run the VI and use any infrared remote control to test your application. Pressing a button quickly on theremote control should cause iTunes to play/pause the current song (iTunes will first open if currently closed). Holding down a remotecontrol button should cause iTunes to play the next song in the current playlist.

4) Experiment to find out how far away you can use your remote control before the infrared receiver no longer works. Try adjusting the detection threshold to maximize transmission distance without false positives.

5) Though infrared photodiodes are not very responsive to visible light, the signal produced could be slightlyaffected by the ambient light in your room. Try operating the circuit in different lighting conditions and note how the signallevel changes.

Post-lab questions

1) What could be done to increase the working distance of your remote control receiver? Would you implement changes in hardware or software?

2) As mentioned earlier, a phototransistor could have been used instead of a photodiode to receive infrared signals. Reasearch some advantages and drawbacks of using each kind of device. Which do you think would work best? Which sensor costs the most?

3) Experiment with the ActiveX VIs in LabVIEW and see what other applications you can control. How could youmake a PowerPoint slideshow advance when an infrared signal is received by your detection circuit?