GB2326542A - Acoustically controlled lamp dimmer - Google Patents

Description

AN ACOUSTICALLY OPERATED CONTROL DEVICE FOR LIGHTING APPARATUS The present invention relates to an acoustically operated control device for lighting apparatus and more particularly to a such a device that is used to control the illumination brightness of the lighting apparatus.

Devices for controlling the intensity of lighting apparatus are well known particularly in domestic applications (they are often referred to as "dimmer switches"). Such devices generally include a variable potentiometer that is used to control the firing angle of a driving circuit that controls the power delivered to the load. Generally devices of this kind are manually controllable by a rotary knob or the like.

As an alternative to manual operation, such a device can be operated by means of an infra-red remote control. Although convenient, a remote control is relatively expensive, requires a battery power supply, is prone to being lost and requires a special tuning circuit to avoid disturbance of other domestic appliances.

It is also known to control the intensity of light emitted from a lamp by touch.

In such a device touching a conductive part of the base of the lamp (or a pull cord that operates the lamp) causes a capacitance change which can be detected and used to control the power supplied to the bulb either in a step-wise or continuous fashion.

Control of the bulb brightness is only possible by manual interaction with a part of the lamp apparatus. One example of such a device as described in US patent number 4668877.

It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.

According to the present invention there is provided an acoustically operated control device for controlling the power supplied to lighting apparatus, the device comprising an acoustic receiver that converts a sound signal into an electrical signal, an audio frequency amplifier for amplifying the received electric signal, a peak detector circuit for generating a pulse in response to the peak value of the received signal, a capacitor that discharges in response to the pulse, means for generating a trigger in response to the discharge of the capacitor and a phase controlled lighting drive circuit, wherein the trigger causes a phase shift in a switching signal of the driving circuit so as to change the power supplied to the lighting apparatus.

Preferably said means for generating a trigger comprises a clock pulse generator that sends pulses to said capacitor and a comparator for comparing the amplitude or phase of the pulses generated and those sent to the capacitor, whereby when a predetermined amplitude or phase difference is detected said trigger is generated. The acoustic receiver may be a microphone. The control device may be housed within an adapter socket for a plug or alternatively may be housed in an adapter between a bulb and a bulb socket of the lamp.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic block diagram of the control device of the present invention; Figure 2 is a detailed circuit diagram of the control device of figure 1; Figure 3 is an example of an output waveform from an audio amplifier of the present invention; Figure 4 shows the waveform of figure 3 after having been filtered; Figure 5 shows the output of the peak detector of the present invention when supplied with the waveform of figure 4; and Figure 6 illustrates the waveform of the oscillation frequency that charges a capacitor of the present invention when the pulse waveform of figure 5 is present, the waveform being shown for comparative purposes alongside the waveform of the discharging capacitor and the peak detector output.

Referring now to the drawings, the control circuit is used to control the power applied to (and therefore the brightness of) a lamp and is generally comprised of an audio input in the form of a microphone 1 for receiving acoustic signals, signal processing circuitry 2 and a triac driving circuit 3 that controls the supply of mains power to a lamp socket 4.

It will be appreciated that any appropriate input transducer may be used to convert audio waves into voltage or current. In this exemplary embodiment a microphone 1 presents a signal to a low pass filter 5 which filters out any high frequency signal greater than 10KHz to eliminate signals generated by unwanted noise. The signal is then amplified by an audio amplifier 6 having a variable gain that may be adjusted by the user. The output of the amplifier 6 is coupled to the input of a high pass filter 7 which attenuates the low frequency elements of the signal. The output of the high pass filter 7 is coupled to the input of a peak detector 8. The peak detector 8 operates as is well known to the skilled person in the art to provide a peak signal which varies as a function of the peak amplitude of the audio signal presented by the amplifier 6. The output of the positive peak detector 8 is coupled to an input of a capacitor switching circuit 9 to discharge a capacitor in a charge transfer circuit 10.

The output of the charge transfer circuit 10 is fed to a triac driver circuit 11 that controls the power applied to the lamp (not shown). The driving circuit 11 controls the phase of the firing signal applied to a triac (not shown) and thereby determines the intensity of the illumination of the lamp.

The control circuit is shown in more detail in figure 2. The microphone 1, low pass filter 5, amplifier 6 and high pass filter 7 are of conventional design and being well understood by the skilled person in the art will not be described any further.

Figure 3 shows a typical signal waveform that is output from the amplifier 6 in response to a sound generated by the clapping of the hands of the operator. This signal is smoothed by the high pass filter 7 whose output is shown in figure 4.

The output from the high pass filter 7 is connected to the base of a pnp transistor T1 that forms the peak detector 8 with capacitor C1 which is connected to the collector of transistor T1. When the magnitude of the output signal from the high pass filter 7 falls below -0.2V (the reverse bias voltage drop across the base-emitter of transistor T1) transistor T1 is turned on thereby allowing the capacitor C1 to be charged. It will be seen that the signal from the high pass filter 7 (shown in figure 4) is an oscillation that repeatedly rises above and falls below the drop voltage of baseemitter of transistor T1. When the signal exceeds -0.2V transistor T1 is turned off and charging of capacitor C1 is temporarily halted until the signal falls again to below -0.2V. The resultant peak detector output waveforsm, shown in figure 5, comprises a near vertical line 1 5a which, as can be seen from the inset to figure 5, comprises an accumulation of capacitor charging steps 1 Sc. The final maximum value output from the peak detector 8 is representative of the maximum output voltage of the high pass filter 7.

After the filtered acoustic signal has been received and transistor T1 has been turned off, the capacitor C1 is able to discharge through resistors R1 and R2. The discharge waveform 1 sub is shown in figure 5.

The output of the peak detector circuit 8 is connected to the base of a transistor T2 which is in turn connected in parallel to a capacitor C2. The capacitor C2 and a series resistor R3 combine to form the charge transfer circuit 10.

Capacitor C2 is connected between the triac driving circuit 11 and ground.

The triac driving circuit 11 comprises a commercially available integrated chip such as that supplied by Siemens Aktiengesellschaft under part number SLB 0586. This chip is designed to be a touch sensitive dimmer control circuit for a lamp and controls the power applied to a load such as a lamp by altering the phase of the firing signal applied to a triac (not shown) in response to touch. The chip includes a clock which generates pulses that are used, in the present invention, to charge C2.

Referring now to figure 6, when the output of the peak detector 8 rises above 0.7V transistor T2 is switched on and presents a short circuit to capacitor C2. The capacitor C2, which was previously fully charged via the clock signal of the triac driving circuit 11, is then discharged through transistor T2 to ground as is represented by the second waveform in figure 6. As capacitor C2 discharges clock pulses are still received from the triac driving circuit 11 and attempt to re-charge the capacitor C2.

However, the pulses are attenuated as a portion of the charge is lost to ground while transistor T2 is still on. The attenuation of the clock frequency pulses is shown at the top part of figure 6 as coinciding with the discharge and recharging of capacitor C2.

By the time the output of the positive peak detector 8 falls below 0.7V capacitor C2 has virtually reached full charge, transistor T2 is switched off and the clock pulses resume to full amplitude.

The attenuated clock pulses are compared with the original clock pulses within the integrated chip of the triac driving circuit 11. When a predetermined difference in amplitude or phase between the two sets of pulses is sensed a trigger is generated that causes a change in the firing phase of the triac. The generation of the trigger and the subsequent control of the triac is all performed within the commercially available chip and, being well understood by the skilled person, is not described in detail here. The phase of the firing signal applied to the triac is dependent on how many previous pulses have been received within a given time period. For example, for the first pulse received the firing angle phase is set so that a light intensity of a quarter of the maximum is attained, on the second pulse received the light intensity is adjusted to half of the maximum by changing the firing angle phase. By the fifth pulse the lamp intensity is switched from full intensity to off and the cycle commences again.

In an alternative embodiment capacitor C2 is connected in series with the collector of transistor T2. In this embodiment the capacitor C2 acts as a coupler and is discharged to ground via the collector - emitter interface of transistor T2. The same discharge waveform as that shown in figure 6 is obtained when the transistor T2 is on.

The control device described above is housed within a plug adapter socket 4 into which the plug of the lamp is received. The adapter is then plugged into a wall socket of the mains supply and the lamp is ready for use. Alternatively, the control device can be housed within an adapter that is connected between the bulb and the bulb receiving socket of a lamp.

In use the lamp is initially turned on by the user clapping his/her hands or snapping his/her fingers. Subsequent claps or snaps have the effect of increasing the brightness of the lamp until full brightness is achieved on the fourth clap. The lamp is switched off on the fifth clap. It will be appreciated that the circuit could be designed to increase the lamp brightness in any number of discrete steps.

Claims (6)

1. An acoustically operated control device for controlling the power supplied to lighting apparatus, the device comprising an acoustic receiver that converts a sound signal into an electrical signal, an audio frequency amplifier for amplifying the received electric signal, a peak detector circuit for generating a pulse in response to the peak value of the received signal, a capacitor that discharges in response to the pulse, means for generating a trigger in response to the discharge of the capacitor and a phase controlled lighting drive circuit, wherein the trigger causes a phase shift in a switching signal of the driving circuit so as to change the power supplied to the lighting apparatus.

2. An acoustically operated control device according to claim 1, wherein said means for generating a trigger comprises a clock pulse generator that sends pulses to said capacitor and a comparator for comparing the amplitude or phase of the pulses generated and those sent to the capacitor, whereby when a predetermined amplitude or phase difference is detected said trigger is generated.

3. An acoustically operated control device according to claim 1 or 2, wherein the acoustic receiver is a microphone.

4. An acoustically operated control device according to anyone of claims 1 to 3 wherein the control device is housed within an adapter socket for a plug.

5. An acoustically operated control device according to anyone of claims 1 to 3, wherein the control device is housed in an adapter between a bulb and a bulb socket of the lamp.

6. An acoustically operated control device for controlling the power supplied to lighting apparatus, substantially as hereinbefore described with reference to the accompanying drawings.