GB2245119A - Remote control circuit - Google Patents

Abstract

Remote control circuits can operate according to carrier mode or according to flash mode. Integrated circuits for processing the received IR (Infra-Red) flash-mode signals are much more expensive than integrated circuits designed for carrier mode. It is an object of this invention to reduce the costs of circuits which process flash mode signals by using integrated circuits designed for carrier mode operation. According to the invention the processor 4 for the remote control receiver is of the type designed for carrier mode. The input circuit for the said processor 4 is dimensioned in such a way that the duration of the received flash mode pulses is increased. <IMAGE>

Description

REMOTE CONTROL CIRCUIT The invention relates to a remote control circuit for domestic electronic equipment. Remote control circuits of this kind may work according to so-called carrier mode or according to so-called flash mode.

When operating in the carrier mode a light emitting diode transmits an IR (Infra-Red) signal to the light receiving diode of the controlled device. The IR signal consists of a burst including a number of oscillations with a typical frequency of 40 kHz and having a duration of approximately 600 ps. Between two successive bursts a gap without oscillations of approximately 600 ps duration is provided. The duration of the burst determines whether a digital "O" or "1" is being transmitted. A long burst may indicate value 1 and a short burst may indicate value 0. In another form the frequency of the oscillations of the bursts is varied by a small amount the higher frequency indicating value 1 and a lower frequency indicating value 0 for example.

Within flash mode instead of such bursts only one single pulse with a duration of for instance 10 - 30 ps is transmitted the distance between successive pulses may be varied between 2 - 8 ms. Said time between successive pulses determines the transmitted value 1 or 0.

In this mode the diodes of the remote control unit and those of the receiver at the controlled equipment are turned on during said pulse and turned off between said pulses. Flash mode has the advantage that due to the very short pulses only small mean energy is used for transmitting the remote control signal. On the other hand, however, processors or integrating circuits needed within the receiver at the equipment and destined for flash mode are more expensive by a factor of about 40 than corresponding processors for carrier mode. This is due to the fact that pulses of flash mode are too short for controlling processors destined for carrier mode so that for flash mode special processors are necessary which can be controlled by said short flash mode pulses.

It is an object of the invention to simplify the circuit at the receiver for flash mode operation.

According to the invention the processor for flash mode operation is of the type designed for carrier mode remote control and the input circuit is dimensioned in such a way that duration of flash mode pulses fed thereto is increased.

The invention is based upon the following considerations. Up to now it was suggested that a processor or integrated circuit designed for carrier mode cannot work for flash mode due to the short duration of the flash mode pulses. However, it was found out that the carrier mode processor can be used for flash mode having said short pulses. This is due to the fact that an input circuit connected to said processor for carrier mode and being supplied with short flash mode pulses does increase the duration of said pulses automatically from about 10 - 30 ps to about 400 gs. So due to the action of the input stage for the processor, carrier mode IR processors will work in flash mode in spite of the short duration of the flash mode pulses.

The main advantage achieved by the invention consist of the fact that a carrier mode processor is cheaper by a factor of about 40 than a flash mode processor used up to now for flash mode remote control. Furthermore the same circuit including said input stage and said carrier mode processor may be used for carrier mode as well as for flash mode operation without any modifications.

According to one embodiment of the invention within the input stage the light receiving diode is connected to the "+" input and further via an AGC cir cuit to the "-" input of an operational amplifier the output of which is connected to the input of the processor. Preferably a negative feedback resistor is provided between the output and the 11 ~ 1t input of the amplifier. The lt input of said amplifier preferabl is connected to ground by a capacitor. In one form of the invention said carrier mode processor is of a similar type to the Sony IC CX20106A. However, any other similar type of processor or integrated circuit may be used.

In order that the invention may more readily be understood, a description is now given by way of example only, reference being made to the drawing. Within the drawing Figure 1 shows an example for the input stage and the processor and Figure 2 shows waveforms of signals in Figure 1.

In Figure 1 the light sensitive diode 1 receives an IR (Infra-Red) remote control signal RC from a remote control unit which is not shown. The diode 1 is connected to the "+" input of the operational amplifier 2 and further via the AGC circuit to the input of amplifier 2. Between output and the "-" input of amplifier 2 a negative feedback resistor R is provided and the said negative input is connected to ground via capacitor C. The output of the amplifier 2 is connected to control input b of integrated circuit 4 which delivers the corresponding signals for controlling the special functions of the equipment controlled by the remote control unit.The AGC circuit 3 additionally enables a desired adaption of the circuit the light level within the room in such a way that for a substantially fixed level of ambient light no output signal is produced whereas with sudden increase in light due to reception of a flash of IR an output signal does arise.

Figure 2a shows short pulses at point "a" with a duration of about 20 ps and a distance of about 2 - 8 ms said distance varying according to the transmitted signal that means the two values 1 and 0 of the digital signal. If one such short pulse comes along a negative output pulse at point b is produced which in a desired way is much more longer than short pulse according to Figure 2a. This effect bases on the operation of the AGC circuit 3 together with resistor R and capacitor C. Due to this operation after short pulse according to Figure 2a has disappeared the output at point b is stretched to a duration of about 400 ps.

This pulse is long enough to properly trigger or control circuit 4 so that a special circuit adapted for short pulses is not needed.

The invention makes use of the unexpected effect that the circuit according to Figure 1 including the input stage and circuit 4 in this form designed for carrier mode operation works very well in flash mode operation without any modification. This is based on the fact that the input stage provided for the purpose mentioned advantageously modifies the duration of short pulses fed thereto in such a way that the circuit 4 which is normally not suitable for said short pulses can operate correctly.

Claims (6)

1. Remote control circuit for a domestic electronic equipment operating according flash mode including a light emitting diode and a light receiving diode connected via an input circuit to a processor controlling the respective operations within said equipment, characterized in that said processor is of the type designed for carrier mode remote control and that the said input circuit is dimensioned in such a way that duration of flash mode pulses fed thereto is increased.

2. Circuit according to Claim 1, characterized in that the light receiving diode is connected to the "+" input and further via an AGC circuit to the "-" input of an operational amplifier the output of which is connected to the input of said processor.

3. Circuit according to Claim 2, characterized in that a negative feedback resistor is provided between the output and the "-" input of the amplifier.

4. Circuit according to Claim 3, characterized in that the "-" input of said amplifier is connected to ground by a capacitor.

5. Circuit according to Claim 1, characterized in that said processor is of the type similar to the Sony IC CX20106A.

6. Circuit as described within the description and shown within the drawing.