How Remote-Control Systems Work
This chapter covers various remote-control systems, troubles that might develop, and what to do when they don’t work.
The first TV remote “wireless” controls used ultrasonic frequencies in the 35- to 45-kHz range. Some of the Zenith remotes used hammers (clickers) to strike tuned metal rods (usually four) in the hand unit to produce (ring) one ultrasonic control frequency. With this set up, you could rattle a key chain and make the TV go off/on or change channels. These early model remotes produced only four to eight analog frequencies. Some later-model
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CONTENTS AT A GLANCE How Remote-Control Systems Work
The ultrasonic remote transmitter The infrared (IR) remote-control
transmitter
Universal remote-control device Intelligent remote-control system Sony’s RM-AV2100 universal
learning remote
Programming the learning remote
Tips on Macro Programming Designing user-friendly macros
Programming the Sony Universal Learning Remote
To view cable TV programs For viewing DVD programs For viewing VCR tapes
Scrolling commands for the Sony RM-AV2100
Remote Control Selection Radio Shack VCR Programmer
Magnavox remotes generated ultrasonic control pulses and would have 10 or more remote control functions.
Some modern-day remote controls are shown in Figs. 9-1 and 9-2. Remote units now control TVs, VCRs, camcorders, stereo audio units, cable TV converter boxes, DBS satel- lite receivers, laser CDs, and much more. Of course, many multi-type remote controls will operate several different devices at the push of a button.
THE ULTRASONIC REMOTE TRANSMITTER
The ultrasonic remote control was used in the older TVs and very few of these systems are now in use. These remotes transmitted on an ultrasonic frequency range of 35 kHz to 45 kHz.
A few models would generate 10 to 15 control pulses that could be decoded in the TV receiver for more logic control functions. A simplified circuit drawing of an ultrasonic remote-control unit is shown in Fig. 9-3.
THE INFRARED (IR) REMOTE-CONTROL TRANSMITTER
Modern remote controls use an infrared (IR) carrier frequency that is pulse-code modu- lated. The carrier frequency is approximately 35 kHz to 55 kHz. The pulses sent out are multiple cycles of usually 20 bits each that modulate the carrier. The logic coding is dif- ferent for various devices, so only a particular remote will operate a device. However,
FIGURE 9-1 Some current-model remote-control hand units for controlling TV receivers.
HOW REMOTE-CONTROL SYSTEMS WORK 313
FIGURE 9-2 A lineup of current remote-control devices used for DBS satellite receivers and cable TV control set-top boxes.
Frequency adjustment variable capacitor
Transistor oscillator
9-volt batt.
C5
C1 C2 C3
C4
Control button function switches R1
Transducer pick-up device on TV receiver
35-45 kHz frequency range ultrasonic transducer
FIGURE 9-3 Simple circuit of an ultrasonic remote-control hand unit used to control older-model TV sets.
a universal remote can be reprogrammed for many different kinds of devices and multi- purpose remote control units are also supplied with many TVs and VCRs. A block dia- gram of an infrared digital remote-control transmitter is shown in Fig. 9-4.
Figure 9-5 shows the infrared remote receiver located within a TV, VCR, etc. The IR signal is picked up by an IR diode sensor on the front panel of a TV and is amplified and pulse decoded. The pulse codes are then sent to a remote-control microprocessor IC, which then sends control voltages to various parts of the TV circuits to control the set’s operation, such as power on/off, volume control, etc. Figure 9-6 shows a typical color TV remote transmitter.
Digital control and coding
IC Touch code control pad
6 volt battery
+ -
(Pulse code)
Remote control case xtal
FIGURE 9-4 A block diagram of an infrared (IR) digital remote-control transmitter.
Set turn on/off AC power control Sound mute Volume control Picture controls Screen readouts Channel control Change to tuner Color controls
IC Remote control MP-Microprocessor Pulse
chip decoder
5vdc 5vdc
5vdc IC
IR signal Photo amp.
pick-up IR diode
sensor Signal from Remote
hand unit (IR) To TV set circuit control functions
From 5vdc power supply
FIGURE 9-5 A block diagram of the remote-control infrared (IR) circuits within the TV receiver.
What to do when the remote control will not work Remote-control units do not fail very often, unless they have been dropped, thrown around, or dunked in some kind of liquid. If your remote equipment does not work, make these quick checks:
1 If your TV (or other device) has a master on/off/manual/remote switch, be sure that it is in the Remote position.
2 If it has a multi-function control, be sure that it is not in the VCR function mode when you are trying to operate the TV.
3 If you have a universal remote unit, it might have become deprogrammed or programmed for the wrong model. Also, if the battery has been replaced, it will need to be reinitialized.
4 Speaking of batteries, you should now be sure that the battery is in good condition, with clean, corrosion-free contacts.
Install a new known-good battery or use a dc voltmeter for a voltage check. The battery should be checked while under load in the remote unit. With the voltmeter connected to
HOW REMOTE-CONTROL SYSTEMS WORK 315
FIGURE 9-6 A color TV remote-control hand unit with the callouts for its various operational functions.
battery terminals, press any button and see if the voltage drops more than 10%. If it does replace the battery with a new one. You can also use a battery tester meter because it puts the correct load on the battery for a valid test.
5 Be sure that you are using the correct remote unit because they look alike and some homes might have six or more various remote controls.
6 The problem could be in the TV or VCR that you are trying to operate. See if the TV or VCR will operate manually. If it does, try another remote, such as a universal one to de- termine if it is the remote control or TV/VCR.
7 To find out if your remote unit is transmitting an IR signal, you can use an IR detector card (Fig. 9-7). The card will show a red pulsing spot on the card if the control is trans- mitting. However, this does not indicate if it is sending out the correct pulse codes.
These cards are available at electronic parts stores.
8 If the control unit has gotten wet, you might still be able to save it. As soon as possible, flush the unit in clean water and if you can take the case apart, use a hair dryer to com- pletely dry out the case and circuit board. Then clean the battery contacts and install a new
FIGURE 9-7 Testing a remote IR transmitter with an IR detection card.
battery. It might keep on clicking. It’s worth a try and you might not have to buy a new remote control.
UNIVERSAL REMOTE-CONTROL DEVICE
The Radio Shack universal remote control can replace many types of standard remote con- trols. These units are preprogrammed and do not have to “learn” commands from the orig- inal remote. Just “tell” this unit what remote control you want to replace (by entering the three-digit codes shown for many brands (Fig. 9-8) and the 3-in-1 universal remote control does the rest.
How to program the universal remote Follow these steps to set up the 3-in-1 remote:
1 Check or install new batteries before programming the unit.
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1 2 3
4 5 6
7 8 9
0 TV VCR CBL
PWR
PROG MUTE
VOL CHAN
REW FF
STOP PLAY