I R control
From:www.sbprojects/
There is no doubt that remote controls are extremely popular and it has become very hard to imagine a world without them.They are used to control all manner of house appliances like the TV set,the stereo,the VCR,and the satellite receiver.Whenever such an appliance reaches the end of its lifetime its remote control becomes obsolete.And since wasting it is a shame we probably all have some old remote controls lying around somewhere.Wouldn't it be nice to use them again to control other things,li
ke for instance the lights in the living room or the curtains?
But sometimes it is the other way around and it is the remote control that dies first.After all it is a hand held device which is often dropped to the floor.Some even have a drinking problem,when someone spills some drinks over it.Others become a victim of man's best friend.
This corner of my site is going to cover Infra Red based remote control projects.These projects will vary from very easy testers to a complete IR receivers which can be used to control all manner of things.Only time will tell what is going to be covered here,so please do come back regularly if you're interested in this subject.
If you want to learn about the theory of operation of IR remote controls you may want to visit my knowledge base first.There I explain the basic principles of IR remote controls.
IR Remote Control Theory
The cheapest way to remotely control a device within a visible range is via Infra-Red light.Almost all audio and video equipment can be controlled this way nowadays.Due to this wide spread use the required components are quite cheap,thus making it ideal for us hobbyists to use IR control for our own projects.
This part of my knowledge base will explain the theory of operation of IR remote control,and some of the protocols that are in use in consumer electronics.
Infra-Red Light
Infra-Red actually is normal light with a particular colour.We humans can't see this colour because its wave length of950nm is below the visible spectrum.That's one of the reasons why IR is chosen for remote control purposes,we want to use it but we're not interested in seeing it. Another reason is because IR LEDs are quite easy to make,and therefore can be very cheap.
A digital camera can see the IR light
爱之战Although we humans can't see the Infra-
Red light emitted from a remote control
doesn't mean we can't make it visible.
A video camera or digital photo camera
can"see"the Infra-Red light as you can see
亲男人哪里让他最上瘾in this picture.If you own a web cam
you're in luck,point your remote to it,
press any button and you'll see the LED
flicker.
Unfortunately for us there are many more sources of Infra-Red light.The sun is the brightest source of all,but there are many others,like:light bulbs,candles,central heating system,and even our body radiates Infra-Red light.In fact everything that radiates heat,also radiates Infra-Red light. Therefore we have to take some precautions to guarantee that our IR message gets across to the receiver without errors.
Modulation
Modulation is the answer to make our signal stand out above the noise.With modulation we make the IR light source blink in a particular frequency.The IR receiver will be tuned to that frequency, so it can ignore everything else.
You can think of this blinking as attracting the receiver's attention.We humans also notice the blinking of yellow lights at construction sites instantly,even in bright daylight.
In the picture above you can see a modulated signal driving the IR LED of the transmitter on the left side.The detected signal is coming out of the receiver at the other side.
In serial communication we usually speak of'marks'and'spaces'.The'space'is the default signal,which is the off state in the transmitter case.No light is emitted during the'space'state. During the'mark'state
of the signal the IR light is pulsed on and off at a particular frequency. Frequencies between30kHz and60kHz are commonly used in consumer electronics.
At the receiver side a'space'is represented by a high level of the receiver's output.A'mark'is then automatically represented by a low level.
Please note that the'marks'and'spaces'are not the1-s and0-s we want to transmit.The real relationship between the'marks'and'spaces'and the1-s and0-s depends on the protocol that's being used.More information about that can be found on the pages that describe the protocols. The Transmitter
The transmitter usually is a battery powered handset.It should consume
as little power as possible,and the IR signal should also be as strong as
possible to achieve an acceptable control distance.Preferably it should be
shock proof as well.
Many chips are designed to be used as IR transmitters.The older chips
were dedicated to only one of the many protocols that were invented. Nowadays very low power microcontrollers are used in IR transmitters for the simple reason that they are more flexible in their use.When no button is pressed they are in a very low power sleep
mode,in which hardly any current is consumed.The processor wakes up
to transmit the appropriate IR command only when a key is pressed.
Quartz crystals are seldom used in such handsets.They are very fragile
and tend to break easily when the handset is dropped.Ceramic resonators
are much more suitable here,because they can withstand larger physical
shocks.The fact that they are a little less accurate is not important.
The current through the LED(or LEDs)can vary from100mA to well over1A!In order to get an acceptable control distance the LED currents have to be as high as possible.A trade-off should be made between LED parameters,battery lifetime and maximum control distance.LED currents can be that high because the pulses driving the LEDs are very short.Average power dissipation of the LED should not exceed the maximum value though.You should also see to it that the maximum peek current for the LED is not exceeded.All these parameters can be found in the LED's data sheet.
A simple transistor circuit can be used to drive the LED.A transistor with a suitable HFE and switching speed should be selected for this purpose.
The resistor values can simply be calculated using Ohm's law.Remember that the nominal voltage drop over an IR LED is approximately1.1V.
The normal driver,described above,has one disadvantage.As the battery voltage drops,the current th
john coffeyrough the LED will decrease as well.This will result in a shorter control distance that can be covered.
An emitter follower circuit can avoid this.The2diodes in series will limit the pulses on the base of the transistor to1.2V.The base-emitter voltage of the transistor subtracts0.6V from that, resulting in a constant amplitude of0.6V at the emitter.This constant amplitude across a constant resistor results in current pulses of a constant magnitude.Calculating the current through the LED is simply applying Ohm's law again.
The Receiver
Many different receiver circuits exist on the market.The most important selection criteria are the modulation frequency used and the availability in you region.
传奇 王菲In the picture above you can see a typical block diagram of such an IR receiver.Don't be alarmed if you don't understand this part of the description,for everything is built into one single electronic comp
李宇春 滴滴答onent.
The received IR signal is picked up by the IR detection diode on the left side of the diagram.This signal is amplified and limited by the first2stages.The limiter acts as an AGC circuit to get a constant pulse level,regardless of the distance to the handset.
As you can see only the AC signal is sent to the Band Pass Filter.The Band Pass Filter is tuned to the modulation frequency of the handset unit.Common frequencies range from30kHz to60kHz in consumer electronics.
The next stages are a detector,integrator and comparator.The purpose of these three blocks is to detect the presence of the modulation frequency.If this modulation frequency is present the output of the comparator will be pulled low.
As I said before,all these blocks are integrated into a single electronic component.There are many different manufacturers of these components on the market.And most devices are available in several versions each of which are tuned to a particular modulation frequency.
Please note that the amplifier is set to a very high gain.Therefore the system tends to start oscillating very easily.Placing a large capacitor of at least22µF close to the receiver's power connections is mandatory to decouple the power lines.Some data sheets recommend a resistor of 330Ohms in series with the power supply to further decouple the power supply from the rest of the circuit.
There are several manufacturers of IR receivers on the market.Siemens,Vishay and Telefunken are the main suppliers here in Europe.Siemens has its SFH506-xx series,where xx denotes the modulation frequency of30,33,36,38,40or56kHz.Telefunken had its TFMS5xx0and TK18xx series,where xx again indicates the modulation frequency the device is tuned to.It appears that these parts have now become obsolete.They are replaced by the Vishay TSOP12xx,TSOP48xx and TSOP62xx product series.
Sharp,Xiamen Hualian and Japanese Electric are3Asian IR receiver producing companies. Sharp has devices with very cryptic ID names,like:GP1UD26xK,GP1UD27xK and GP1UD28xK, where x is related to the modulation frequency.Hualian has it's HRMxx00series,like the HRM3700and HRM3800.Japanese Electric has a series of devices that don't include the modulation frequency in the part's ID.The PIC-12042LM is tuned to36.7kHz,and the PIC12043LM is tuned to37.9kHz.
The End?
This concludes the theory of operation for IR remote control systems intended for use in consumer electronics.I realize that other ways exist to implement IR control,but I will limit myself to the description above.One of the issues not covered here is security.Security is of no importance if I want to control my VCR or TV set.But when it comes to opening doors or cars it literally becomes a'key'feature!Maybe I will cover this issue later,but not for now.
I also realize that my small list of manufacturers is far from being complete.It is hardly possible to list every manufacturer here.You can send me an e-mail if you have details about other protocols that you feel should be added to my pages.
This page only described the basic theory of operation of IR remote control.It did not describe the protocols that are involved in communication between transmitter and receiver.Many protocols are designed by different manufacturers.You can find the protocols of some manufacturers in the link section at the top of this page.
ITT Protocol
The ITT IR protocol is a very old one.It differs from other protocols in that it does not use a modulated carrier frequency to send the IR messages.A single command is transmitted by a total of
14pulses with a width of10µs each.The command is encoded by varying the distance between the pulses.
This protocol used to be very reliable and consumes very little power ensuring long battery life. One big disadvantage of this old protocol is that it sometimes triggers false commands,for instance when you put a laptop computer with an active IRDA port close to the IR receiver.
Many consumer electronics brands used this protocol in Europe.Among them were:ITT,Greatz, Schaub-Lorenz,Finlux,Luxor,Salora,Oceanic and later also Nokia,to name but a few. Features
•Only14very short IR pulses per message
•Pulse distance encoding
•Long battery life
•4bit address,6bit command length
•Self calibrating timing,allowing only simple RC oscillator in the transmitter
•Fast communication,a message takes from1.7ms to2.7ms to transmit
Protocol
An IR message is transmitted by sending14pulses.Each pulse is10µs long.Three different time
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