Lab_5b_2C_2009 - ECE 2C Laboratory Manual 5b Putting it all...

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1 © Bob York ECE 2C Laboratory Manual 5b Putting it all Together ….continuation of Lab 5a In-Lab Procedure At this stage you should have your transmitter circuit hardwired on a vectorboard, and your receiver circuit tested and debugged on a solderless breadboard. 5.1 Basic System Demo and Characterization We are now ready to put together our complete communications link as shown in Figure 5-1. The transmitter and receiver each have their own separate power supply; one of these is the supply you built in ECE 2B. The output of the demodulator section on the receiver is connected to the audio-amplifier system that you built in an earlier lab. IR Tx DC Supply Modulation Source IR Rx DC Supply Audio Amplifier R Figure 5-1 –System block diagram. The modulation source can be the bench function generator, your microphone circuit, an iPod/MP3 player, or any other audio source. A simple sinusoidal tone from a function generator is best for testing the system initially, as we can sweep this source to determine the overall frequency response. Construct the circuit in Figure 5-1 using the bench function generator as a modulation source. This should be essentially the point at which you left off the previous lab. Start with a transmitter-receiver spacing of around 0.5m R . Our ultimate goal will be to
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2 Putting it all Together © Bob York 2 have the system operate well over a wide range of transmitter-receiver separations, but it is easiest to start with smaller separations and work our way up. Be sure to include ground connections between all circuits! Set the modulation source to a 1 kHz sinusoid, and adjust the amplitude so that the duty- cycle of the transmitted signal varies by around 20% at the peak. It is not necessary to hit this modulation depth precisely; we just don’t want to over -modulate the system at this stage. If the system is functioning properly you should be able to hear the tone on your audio speaker system (keep the volume down please!). Observe the output of the receiver system on the oscilloscope. You should observe a reasonably clean sinewave, although zooming in on the waveform will show some residual of the 40kHz carrier superimposed. Do not proceed past this point until your system is functioning as a complete link. You may need to bring the transmitter and receiver a little closer together. You may also need to adjust potentiometer R23 in the signal-conditioning circuit. Determine the maximum range of your system by slowly moving the transmitter and receiver apart. Record this number. Experiment with the modulation depth (amplitude of the modulating signal) and record your observations. 5.2 Increasing the Operating Range Directionality of the Emitter and Detector Diodes The system requires that the transmitter LED is oriented towards the detector for best results.
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This note was uploaded on 12/28/2011 for the course ECE 2C taught by Professor Yue during the Fall '08 term at UCSB.

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Lab_5b_2C_2009 - ECE 2C Laboratory Manual 5b Putting it all...

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