exercise 2: ir remote control - lab-volt manual 334 facet by lab-volt the infrared controller...

Student Manual

334 FACET by Lab-Volt

The Infrared Controller Transducer Fundamentals

Exercise 2: IR Remote Control

EXERCISE OBJECTIVE

When you have completed this exercise, you will be able to describe how digital data is transferred via

infrared light, demonstrate typical data encoding and decoding techniques used in IR remote control

applications, and explain how infrared light can be used to remotely control electronic equipment. You will

use an oscilloscope to make observations and measurements.

DISCUSSION

Digital data consists of logical highs and lows that can be represented by a light source being turned on or

off, respectively.

The INFRARED CONTROLLER circuit block on your circuit board uses this technique by turning its IRED

on and off to create the digital pulses.

Digital data that is transmitted via IR light can be received by an IR detector.

The INFRARED CONTROLLER circuit block on your circuit board can be used to

simulate the IR remote control operations of an electronic device, such as a TV or

VCR.

You can transfer various codes over the IR data link that a device can recognize as

commands, such as “increase volume,” or “power off.”

Student Manual

FACET by Lab-Volt 335

Transducer Fundamentals The Infrared Controller

Many digital electronic products contain microprocessors that use parallel address and data buses for

processing data.

Therefore, it is often necessary to convert parallel data to serial data before transmitting the data with an

IR emitter.

Likewise, the serial data received by the IR detector must be converted to parallel data before it can be

used by a microprocessor or similar circuitry.

Parallel-to-serial and serial-to-parallel conversions are performed by the data encoder and decoder on

your circuit board.

How many data lines are needed to serially transmit an 8-bit data byte?

a. one

b. two

c. four

d. eight

The encoder on your circuit board serially transmits nine digits of information via the IRED.

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and the last four digits as data.

The encoder and decoder can be used to address many different devices by assigning a unique address

communication link will be established.

The encoder on your circuit board outputs trinary data and address information, which has three logic

states: low, high, and open.

5) devices, whereas only

32 (25) binary addresses would be possible.

The encoder and decoder use two consecutive pulses to represent each logic state that is needed to

convey information.

Two short pulses in succession represent a logical low.

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Two longer pulses represent a logical high,

A long pulse followed by a short pulse represents a logically open state.

Using the image below, try to decode this waveform and select the correct logical states of the four trinary

digits.

a. LOW, HIGH, OPEN, LOW

b. HIGH, LOW, OPEN, HIGH

c. LOW, HIGH, LOW, OPEN

d. OPEN, HIGH, OPEN, LOW

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The open state is caused by an open-circuit condition (no connection) on an input line to the encoder.

A low condition (0 V) or high condition (15 V) on any input line causes a logical low or high pattern,

The encoder converts nine parallel input lines of information to 18 serial pulses.

Two pulses form a pattern that represents each trinary digit. The nine trinary digits represent the input

information and can be transmitted serially over the IR link.

four parallel binary data bits.

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The decoder accepts the trinary addresses, but converts the data to binary by interpreting an open state

as a logical high.

Eighteen pulses are needed to transmit the 9 trinary digits because

a. two pulses represent each trinary logic state.

b. only half of the pulses are actually used.

The decoder recognizes the data as being valid only if two identical 9-digit words are received

consecutively.

valid.

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Most remote controllers transmit IR light for distances much greater than those on your circuit board.

This is accomplished by setting the peak power of the IRED very high and using a common modulation

technique to reduce the average power of the IRED. In this case, the encoder output modulates a higher

(carrier) frequency, which in turn pulses the IRED.

extremely low and the data transfer rate is unaffected by this technique.

This is a partial schematic of the TRANSMITTER section of the INFRARED CONTROLLER circuit block.

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Four DIP switches are used to set the four trinary data input lines for a 4-bit binary value.

Each time you press the XMT pushbutton, the encoder outputs two identical 9-digit words, one after the

other. No signal is sent between the words for a duration of 3 data periods.

If XMT is still pressed after two words are sent, the encoder continues to send the same word.

The output of the encoder drives a transistor that switches the IRED on and off to create pulses of IR

light.

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If you hold down the XMT button on your circuit board, the encoder will continue to send

a.

b. spaces after two words are sent.

c. two sets of identical words.

This is a schematic of the RECEIVER section of the INFRARED CONTROLLER circuit block.

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The photocurrent produced by the photodiode inside the IR detector must be converted to a voltage and

When two identical address and data patterns have been received, the data is deemed valid, the Valid

updates the LED display until new valid data arrives.

If the modulation technique is used at the transmitter, the receiver must include a demodulator in the

signal-conditioning circuitry to remove the high (carrier) frequency pulses.

You can determine the transferred data rate of an IR communication link in bits-per-second (bps) by

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Digital instruction codes are commonly sent via IR light to a device to perform a task or to provide a

For example, a TV may have several different codes to control the power, set the volume, and change the

channels.

off the TV set.

PROCEDURE

In this PROCEDURE, you will make observations and measurements on IR remote control circuitry by

using your oscilloscope.

Insert a two-post connector in the BLOCK ENABLE position of the INFRARED

CONTROLLER circuit block.

Connect the CH 1 probe to the ENCODER OUT test point and the CH 2 probe to DECODER

IN. Be sure to use X10 probes. Ground the scope probes to the GND terminal.

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Set the DATA switches for a value of 3H (0011) by placing switches 1 and 2 in the up

position and switches 4 and 8 down.

To transmit the data (3H), press XMT.

Observe the DATA LEDs in the RECEIVER block. Has the correct data (3H) been received?

a. yes

b. no

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While pressing XMT, compare the transmitted and received waveforms on your oscilloscope.

Also, it might be helpful to go to the UNCAL position of the oscilloscope to sync the

waveforms.

Are the two waveforms similar?

a. yes

b. no

The correct data of 3H has been properly transmitted, received, and displayed. Set the

While pressing XMT, adjust the sync control on your oscilloscope to obtain the waveforms

shown. Also, try adjusting the hold off control on your scope if necessary.

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Continue pressing XMT and observe the received waveform on CH 2 of your oscilloscope.

How many data bits are logically high?

a. 1

b. 2

c. 3

d. 4

While pressing XMT, observe the oscilloscope as you slowly change the position of DATA

switch 4 from down to up.

When DATA switch 4 is moved to its mid-position, what happens to the waveform on CH 2?

a. One pulse goes low.

b. One pulse becomes longer.

c. Two pulses go high.

d. Two pulses become longer.

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Ensure that DATA switch 4 is fully upward. How many data bits are now high?

a. one

b. two

c. three

d. four

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Set the vertical mode to CHOP and the trigger mode to NORMAL. Trigger the scope on

CH 2, with a positive slope.

While pressing XMT, adjust the sync control on your scope for the waveforms shown.

NOTE: The low pulse on CH 1 appears only at the instant you press XMT.

Press XMT several times as you observe the waveform (VT) on CH 1.

NOTE: If your oscilloscope has a single-sweep trigger mode, use it to perform this step.

With each depression of XMT, is the waveform on CH 1 similar to the one shown?

a. yes

b. no

Place all DATA switches down, for 0H.

Set the horizontal sweep on your oscilloscope to 50

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While pressing XMT, measure and record the data period of the received pulses on CH 2.

Remember that two pulses are required for each data bit.

T = s (Recall Value 1)

Based on the measured data period of s (Step 20, Recall Value 1), calculate the

data rate of the received signal in bits-per-second (bps).

data rate = bps (Recall Value 2)

To simulate sending an IR remote code that will change the track on a CD player, set the

DATA switches for a value of AH by placing switches 2 and 8 in the up position and switches

1 and 4 down.

Press XMT to transmit the data.

Observe the DATA LEDs in the RECEIVER block. What data has been received?

a. 5H

b. AH

c. BH

d. 0H

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CONCLUSION

• Digital data is transferred serially over an IR link.

• Parallel-to-serial and serial-to-parallel conversions are often required by controller circuitry.

• Encoding and decoding techniques are used to exchange information, such as device address and

control data.

• Numerous instruction codes can be sent over an IR link to remotely select different functions and

perform various tasks.

• Many different address codes can be sent over an IR link to remotely select and control several

devices.

• Trinary addressing provides a wider address range than binary for the same amount of address lines.

REVIEW QUESTIONS

1. To convert trinary data to binary, the decoder on your circuit board interprets logical

a. lows as highs.

b. highs as lows.

c. opens as highs.

d. opens as lows.

2. What conversion must the encoder perform before it can transmit the data that is set by the four DATA

switches on your circuit board?

a. serial-to-parallel

b. parallel-to-serial

c. binary-to-trinary

d. trinary-to-binary

3. If this waveform were observed at ENCODER OUT on your circuit board, how many trinary data digits

are represented by the pulses shown?

a. one

b. two

c. three

d. four

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4. If you observed this waveform at DECODER IN on your circuit board, how many trinary data digits

are in the open state?

a. one

b. two

c. three

d. four

5. If the data period of an IR remote control signal is 20 s, what is the data bit transfer rate?

a. 5,000 bps

b. 20,000 bps

c. 50,000 bps

d. 100,000 bps

exercise 2: ir remote control - lab-volt manual 334 facet by lab-volt the infrared controller...

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