WO2003100448A1

WO2003100448A1 - Array monitoring

Info

Publication number: WO2003100448A1
Application number: PCT/AU2003/000649
Authority: WO
Inventors: Zhi-Qiang He
Original assignee: Compusign Pty Ltd
Priority date: 2002-05-28
Filing date: 2003-05-28
Publication date: 2003-12-04
Also published as: AUPS261402A0

Abstract

A device (1) having an array of electronically activated components, such as LEDs (2), includes circuitry for illuminating the components (2), e.g. row and column drivers (4, 5), and circuitry for monitoring the current drawn by the individual components (2) or group of components. The monitoring circuitry includes sensing means, e.g. one or more resistors (7), in series or parallel with the driver circuitry, that can be switched into and out of the circuit, e.g. by switches (TS1-TSn). The device (1) may operate in an illumination mode in which the components (2) are driven in a standard manner, and in a test mode, in which one or more of the components (2) are driven and the voltage across the sensing means (7) is monitored, e.g. by A/D converters (8). The devices (1) may communicate with a central control that manages the devices (1) in accordance with the monitoring results. The monitoring results may be logged to record the state of the device (1) at a particular time, e.g. to evidence correct operation. The device (1) may be used in many situations, and could be e.g. a traffic sign or the like.

Description

Array Monitoring

The present invention relates to the monitoring of arrays of components, and relates especially to arrays of light emitting diodes (LEDs), although it may be applied more broadly also.

LEDs are able to provide high illumination, whilst exhibiting low power consumption and long life. They may be mounted together in arrays and may be addressed individually so as to provide different patterns of illumination.

LED arrays are therefore well-suited for use in illuminated signs and other display contexts, especially where the information to be displayed is changed or updated regularly. Accordingly, LED array displays are in widespread use, and are found in many different forms and environments, both indoors and outdoors.

Well-known uses of LED displays include ticker and moving message display boards and the like. These may be mounted throughout a building or other area, and may for example provide finance, news and sports information, as well as promotional and advertising messages.

LED displays may also be found in airports and bus and train stations, where they may be used to display travel information and the like to passengers.

Another increasingly important use of LED displays is in traffic signalling. For example, a LED sign on a freeway might indicate a warning, route information, traffic conditions, speed limits and the like.

Typically, the LEDs of an LED array are connected together in a row and column arrangement, and row and column drivers activate the appropriate LEDs of the array to produce a desired graphic or the like. Thus, the row driver will sequentially connect each row of LEDs to ground, and the column drivers will apply a voltage simultaneously to selected ones of the LEDs in the activated row in order to generate the necessary graphic or image to be displayed. The present invention aims to provide an LED display and the like with extra functionality that may provide various beneficial features to the display.

Viewed from one aspect, the present invention provides an LED device (such as a display or illumination device) having an array of LED components, the device including circuitry for illuminating the LED components and circuitry for monitoring the current drawn by individual LED components or groups of LED components within the array.

By monitoring the currents drawn by individual LED components within the device, the present invention may provide a number of advantages. For example, the present invention enables one to determine if one or more of the LED components are defective, so that suitable remedial action may be taken.

In this regard, the invention can be particularly useful in safety critical situations, such as in traffic road sign applications and the like. In such situations, a damaged LED display could prevent a vehicle driver from receiving important information and/or could cause a driver to receive wrong information.

With the present invention, a LED traffic sign may be monitored, e.g. from a remote central control, and any problems with the sign may be immediately identified and rectified. Further, as well as providing an alert for remedial action, the present invention may allow the condition of the device to be monitored over time. Thus, a log may be kept of the state of the LED components in the array.

This could be advantageous in situations where an operator needs to confirm that a display was working correctly at a particular point in time. It can be particularly important for example in situations in which the display provides guidance that should be followed, e.g. the display of a maximum speed limit.

Thus, a vehicle driver charged with a speeding offence might try to argue that the LED sign displaying the speed limit was defective, and that the sign was either unintelligible or gave an incorrect speed. With current displays, this argument could be very difficult to disprove. With the present invention, however, a log may be kept of the condition of the array LEDs, and this may be suitably recorded (e.g. in a tamper-proof manner) so that the log may be used in court or the like in order to prove that the sign was working correctly. Such evidence may also be used to limit liabilities that could arise from a suggestion that defective signage had caused an accident or the like.

A point to note is that the LED components of the array may take any appropriate form, and could be individual LEDs and/or could be clusters of LEDs, e.g. two or more LEDs addressable together as a single unit/pixel. The LEDs of any array and/or cluster may be all of the same type, or could be of differing types, e.g. have different colours, operating intensities or the like. Also, it may be that groups of LED components within a row may need to be tested together, as opposed to individually, e.g. a specific sub-unit of the LED components that provide a group of pixels on a display. The monitoring circuitry may take any suitable form, and may include separate sensors for monitoring each of the individual LED components. This could however result in a quite complicated and expensive design.

In one preferred embodiment, the monitoring circuitry includes a monitoring sensor for monitoring each row of LED components in the array (one sensor could be common to all rows, or a separate sensor could be provided for each row). This then reduces the number of sensors required, and provides for a less complex and expensive display.

A row sensor may determine the current on a row line during illumination of one or more of the LED components of that line. If this is carried out whilst e.g. a sign is operating in its standard illumination mode, then it will generally be the case that more than one LED component in a row will be lit simultaneously. Therefore, although monitoring of the row current would provide an indication of a problem with those of the LEDs that are meant to be lit, it would not identify the individual LED or LEDs at fault. In order to address this, the LED device may operate in both an illumination mode and in a test mode, wherein in the test mode only one LED component (or one group of LED components) at a time is lit on a row. This then allows each LED component (or group of components) to be monitored independently. A point to note is that the LED components in the array may be switched on and off at a rapid rate, and that sensing can also occur relatively rapidly. Therefore, even though a LED component under test will be illuminated, it will not significantly affect the appearance of e.g. a displayed image or illumination effect, since it will be a short isolated illumination that need not be continually repeated, and so will not be registered by an observer.

Also, as a test may take place relatively quickly, it may occur at any suitable time within the normal operation of the display, e.g. interlaced between the normal illumination controls. For example, a LED display is normally run in a pulsed mode, so that a graphic is actually flashed e.g. 25 times a second rather than constantly illuminated. This still gives the impression of a constant image (due to "persistence of image" of the human eye), whilst reducing the load on the LED components and increasing their working life and the like. It also allows fewer column drivers to be used, as the rows may be scanned so that a column driver may independently activate LED components in more than one row. A test mode may be conducted between a pair of such illumination flashes. Alternatively or also, a test may occur after only one row has been lit, and/or one row may be tested whilst another row is in the illumination mode.

As an alternative to separate illumination and test modes, the display sign may be operated so that only one LED component in a row (or only a specific group of LED elements in a row) is switched on at any one time. The current sensing may then take place during a normal illumination mode. In this case, even where the LED components are individually switched or switched in small groups, the speed of switching may still provide a seemingly constant display.

The row sensor may take any suitable form, and may for example take the form of a resistive element, whose voltage drop is monitored. The resistive element may be placed for example between the LED components of a row of the array and a common ground. The voltage drop will provide an indication of the current drawn by the LED components, and so will provide an indication of the state of the LED components.

The placement of a sensor resistance on a row line may cause problems when operating in a standard illumination mode in which a number of LED components on a row are simultaneously lit. For example, if the resistance is too high, then when e.g. all of the LED components in a row are illuminated at the same time, the total current drawn by all of these LED components will pass through the sensor resistance, and this could result in an unacceptably high voltage drop and possible damage to the device circuitry. If the sensor resistance is reduced to minimise the voltage drop, however, then there may be insufficient resistance to derive a meaningful voltage from it, and this may lead to inaccuracies in the monitoring.

Also, as the number of activated LED components within a row will vary depending on the different images being displayed, then the presence of the sensor resistance within the row will cause the current through the LED components to vary with the number of LED components illuminated. This will vary the brightness of the LED components, dependent upon the image displayed (i.e. the number of LED components lit), and so could be detrimental to the appearance of the displayed image. These effects may not be problematic for displays using only a small number of LED components per row, and, in one embodiment, the problems may be overcome by operating the device so that when e.g. generating a graphic or the like only one LED component per row is illuminated at a time or so that only a small number of LED components are operated at a time. In the latter case, a test mode, as well as a standard illumination mode, may be required to test the LED components individually or in still smaller groups.

In a particularly preferred and beneficial embodiment of the present invention, however, the monitoring circuitry includes sensing circuitry that can be switched into and out of the array circuitry (LED illuminating circuit). This allows the display to be illuminated in a standard manner by activating multiple LED components per row simultaneously (with the sensing circuitry switched out of the array circuitry), and allows the LED components to be tested by switching the sensing circuitry into the array circuitry when a test is to be conducted. A sensor circuit may thus be provided in each row of the array, and the sensor circuit may be switched out of the row circuit when the LED components of that row are being operated to produce a graphic or the like, e.g. when a row is activated by the row driver. Then, when the row driver deactivates the row (disconnects it from ground), the sensor circuit may be switched into the row circuit and one or more of the LED components may be pulsed by the channel driver for testing purposes.

Again, testing may take place at any time, due to the speed with which switching is able to occur.

The sensing circuitry may include a suitable monitoring sensor such as a resistive element whose voltage is monitored. The sensor may be positioned between the LED components of the row and a common sink such as ground. Each row may be provided with its own sensor, or a plurality of rows may be connected to a common sensor. The sensing circuitry may be in series with the row switches, or may be parallel with them (e.g. providing a parallel route to ground).

In the latter case, the switching circuitry could take the form of various input/output ports of a controlling microprocessor. These could be operated to present a voltage level to one side of the row sensor which is equal to that presented at the other side by the column driver (through the LED components). This then prevents current flow along this route, and may provide an inexpensive and simple implementation of the invention needing few extra components. In such an implementation, the row sensor and test switch (I/O port) would be in series with one another.

This implementation may not identify a fault with the row switch or row driver circuitry, as it provides a parallel circuit to ground independent of the row switch. Where the row and test switches are in series, then a fault in the row switch will be picked up in the test. It may not however be possible to use the implementation of the I/O ports. Instead, the switching may be provided by for example a transistor component, such as a MOS-FET transistor, e.g. as used by the row drivers of standard LED displays for turning the rows on and off.

In this case, the switch and row sensor are arranged parallel to one another, with closure of the switch providing a bypass to the sensor during normal illumination.

Thus, a transistor component may be provided on each row for switching a parallel resistive element into and out of circuit with the LED components of the row. A transistor component may also be used in the parallel switch arrangement in place of the I/O ports of the microcontroller. Actuation of such sensor circuit switches may be achieved by using a driver circuit similar to a row or column driver circuit,

The test, row and driver circuits may all be co-ordinated using a microcontroller within the LED device suitably programmed to provide the desired functionality. The microcontroller may receive the outputs from the current sensing circuits, and use the information as appropriate.

In all of the embodiments, the sensing circuitry may take any suitable form, and e.g. any suitable means may be provided for monitoring the voltage across the resistive element. Thus, the voltage could be passed to one or more suitable comparators or the like, which could output a signal dependent on whether the voltage was above or below a set threshold value or values, the threshold value indicating a short circuit, a lower than expected or higher than expected current or the like. In one preferred form, the voltage across the row sensor/resistive element is monitored by an analogue to digital (A/D) converter that outputs a signal proportional to the voltage across the sensor.

The A/D converter may have any suitable accuracy, and may be an 8-bit converter that outputs a voltage value between 0-255. Higher bit converters could also be used if greater accuracy were required, e.g. 9 or 10 bit converters.

When a test current is passed through a LED component, it may last for any suitable length of time, and the voltage applied by the column driver may take any suitable value. In one preferred embodiment, the applied voltage, and preferably also its pulse length, are the same as that used in a normal illumination mode. They could however be different, and where the sensor is switchable into or out of circuit with the row circuitry, it would also be possible, for example, to provide a number of different sensor elements in the test mode, e.g. having different resistive values. Thus, the sensor could be changed, depending on e.g. the types of LED components used in the array. The results obtained from the monitoring circuits for the LED components may be utilised in any suitable manner, and may be stored and/or operated on by means within the LED device itself, e.g. a microprocessor, and/or may be passed to a central control with which the device communicates. The results may for example be analysed or logged or both. The detected voltage may be compared to one or more threshold values to determine whether the LED component is faulty or not. Thus, the actual current passing through the LED component may be determined (e.g. as a value between 0-255 for an 8-bit A/D converter), and this value may be used to determine if there is an open or a short circuit or if an incorrect LED type has been placed in the array. Where the LED component comprises a cluster of LEDs, the current drawn by the cluster may be monitored to check if one or more of its LEDs has become defect. The system will not generally be able to detect which LEDs of a cluster are faulty, only that one or more of them are, due to the change in the current drawn. A more detailed analysis may also be undertaken by correlating the results for the different LED components monitored, e.g. in order to identify other problems that may exist in the display. For example, if only one LED component on a column is found defective, then the LED component itself is probably faulty. However, if all of the LED components of one array column are determined to be faulty, then it may be that the fault is with the column driver rather than with the LED components themselves. Other problems may also be detected, such as power supply or temperature faults or the like.

Instead of or in addition to fault finding and reporting, the monitored information may be logged for future use. The device or system may thus record the time and date at which a test was run together with the resulting test data obtained. Recording may be done in such a manner that the record is tamperproof. This may then provide the record with an evidentiary quality.

Where a log is kept, it may only record whether a LED component was faulty or not, rather than record an actual voltage/current measurement, as this saves on storage memory, although current voltage recordal is also possible.

The monitoring circuitry may monitor all of the LED components of an array. Alternatively or additionally, the monitoring circuitry may only test those LED components of the array that are intended to be illuminated, e.g. that need to be activated in order to generate a particular image that a display is instructed to produce. This latter embodiment satisfies the need to ensure that the LED device is working correctly, e.g. is displaying the correct information, without the need to test all of the LED components and without the need to store the resulting data for all of the LED components. It can therefore provide savings in communications bandwidth, and, more importantly, can provide savings in storage space where a log of the test results is kept. Also, if all of the LED components were tested at the same time, this might in some circumstances be perceivable to an observer, e.g. at night. Testing of only those LED components that are meant to be illuminated can prevent this. The testing of only those components that are required to be illuminated can be seen as effectively comparing those components to be activated with those which will in fact be illuminated.

Once the test results have been appropriately analysed, either by the LED device itself, a central control or both, any suitable action may be taken. For example, an alarm may be raised, an engineer may be sent to repair the faulty device (possibly already knowing what is wrong from a remote diagnostics of the device), the device may be instructed to shut down or to output a failure warning or the like, e.g. a default signal, or the required graphics or the like that are to be generated could be produced using alternative LED components of the array, e.g. the image could be shifted one or more pixels (LED components) either side, or above or below, a faulty pixel or could be reshaped. Also, it would be possible to include back-up LED components for each of the pixels of the array, which could be switched into place on failure of any of the main LED components.

When a LED component comprises a cluster, it may be that no action is required if one LED or a certain percentage of the LEDs in the cluster is faulty, but repair or other action may be required if a certain number are found faulty.

Although the above has mainly focussed on display devices, it should be noted that the invention may also relate to illumination devices, especially those used in safety critical applications.

The feature of logging the condition of the LED components in a LED array device is in itself beneficial, and, viewed from another aspect, the present invention provides an LED device including an array of LED components, means for monitoring a condition of the separate LED components or of groups of the LED components, and means for logging the monitored conditions.

A further feature that is important in itself, is the monitoring of only those LED components of a device that are to be illuminated. Thus, from a further aspect, the present invention provides an LED device including an array of LED components, means for determining which of the LED components are required to be illuminated, and means for monitoring the condition of the LED components that are required to be illuminated.

Also, the feature of using a separate testing mode is itself beneficial, and, viewed from a further aspect, the present invention provides an LED device including an array of LED components, means for operating the LED components in an illumination mode (in which the LED components may be operated simultaneously), and means for operating the LED components in a test mode in which the LED components (or groups thereof) of any one row or column of the array are illuminated individually. Especially beneficial is the feature of switching a sensor into and out of the array circuitry, and, viewed from another aspect, the present invention provides an LED device including an array of LED components, means for illuminating the LED components, and means for monitoring the condition of the LED components, wherein the means for monitoring the LED components includes means for switching a sensor into each row or column of the array for testing purposes.

The provision of a number of LED devices within a system controlled by a central control, and having suitable fault procedures is in itself an important invention.

Thus, viewed from a further aspect, the present invention provides an

LED device (e.g. display or illumination) system including a central control and one or more remote LED array devices, e.g. display or illumination devices, each LED array device including an array of LED components, means for receiving illumination instructions from the central control, means for illuminating the LED components of the array in accordance with the illumination instructions, means for testing the condition of the LED components, and means for communicating information to the central control relating to the results of the test. Viewed from a still further aspect, the present invention provides an LED device control system including one or more LED devices, each having an array of LED components, and a remote central control for controlling the one or more devices, wherein each device includes means for detecting a condition of the array components, and means for sending information to the central control relating to the detected conditions.

The present invention also extends to LED devices for use in such systems, and the systems and devices may include any of the above-mentioned features, including for example alarm, analysing and/or logging features.

The present invention also extends to methods of operating LED devices and LED device systems in accordance with any of the previously discussed features.

LED devices and systems in accordance with the present invention may be utilised in many different applications, e.g. traffic signs, traffic lights, airport landing lights, transport applications generally, such as in rail and bus stations and the like, hospital signage, manufacturing, logistics stock control, advertising and promotional signage and information systems in general. They may also be used in e.g. machinery and instrumentation situations, e.g. for lighting or indicating purposes or the like. Although the above discussion has focussed on LED displays, the present invention may also extend to non-LED displays and other non-LED applications. Thus, the invention is applicable to electronically controlled arrays in general, especially low-voltage electronic arrays. For example, it may be applicable to signs using electro-mechanical elements or incandescent globes, lighting arrays using any suitable lighting elements, and non-lighting and display situations, such as arrays of solenoid activated devices or the like.

Thus, viewed from a further aspect, the present invention provides an electronically-activated array including a plurality of components connected together in a row and column formation to form the array, the components being actuated by an electrical current supplied by one or more array drivers, and wherein the array includes a monitoring circuit for monitoring the current drawn by individual components or groups of components.

Preferably, the monitoring circuit includes a current sensor in each row or column of the array, and preferably, the monitoring circuit is switchable into and out of a row or column circuit, the monitoring circuit being switched out of the row or column circuit when the row or column is under test.

The other above-discussed aspects of the LED device and LED device systems, such as logging and testing only those components to be activated and the like, may also be applied to other electronically-activated array devices and systems.

It will be appreciated that the actual implementation of the invention may take any suitable form, and may use hardware, firmware and/or software as desired. For example, the monitoring circuitry may be provided in any suitable manner, and may lie totally or partially within the controlling microprocessor. The values of the various components, e.g. resistances and the like many take any suitable form depending on the circumstances.

It should be noted also that the invention has been described mainly with respect to the monitoring sensors being row sensors. They could, however, also be provided in the columns of the array. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings. It is to be understood that the particularity of the drawings does not supersede the generality of the preceding description of the invention. In the drawings:

Figure 1 is a schematic of a standard LED display control circuit;

Figure 2 is a schematic of an LED display control circuit in accordance with a first embodiment of the present invention;

Figure 3 is a schematic of an LED display control circuit in accordance with a second embodiment of the present invention;

Figure 4 is a schematic of an LED display control circuit in accordance with a third embodiment of the present invention; and

Figure 5 is a schematic block diagram of an LED display system in accordance with an embodiment of the present invention that might be used e.g. to provide traffic control signs and the like.

Referring to Fig. 1 , a standard LED display 1 typically comprises a plurality of LEDs 2 that are individually addressable so that any number of the LEDs 2 may be illuminated in order to provide a desired image on the display 1.

The LEDs 2 are connected together into an array of n rows (Row Row_n) and m columns (Cι-C_m), and are controlled by a microcontroller 3.

The microcontroller 3 has in-built into it or controls a row driver 4 (represented by switches DSrDS_n), and also controls a column driver 5. These drivers 4,5 activate the LEDs 2.

In use, one of the row switches DSrDS_n is closed to connect all of the LEDs 2 of the corresponding row Row Row_n to a common ground. At the same time, the column driver 5 provides a voltage on a select number of the columns CrC_m, so that a current will flow through the LEDs 2 of those columns.

Thus, the row driver 4 provides a sink for one row of the LEDs 2 at a time, and the column driver 5 simultaneously illuminates those LEDs 2 on the grounded row which the microcontroller 3 has determined need to be lit in order to provide the required sign graphic or the like.

The microprocessor 3 cycles through each row Row Row_n in turn, illuminating the required LEDs 2 of each row. Typically, all of the rows are cycled through once every 25^th of a second, so that the image seen is flashed on the display e.g. at 25 frames per second. Due to persistency of vision, an observer of the display will see a seemingly constant image.

Generally, the LEDs 2 will always be operated at the same brightness level. Their brightness may however be controlled, if desired, by varying the current size and/or the pulse time for the current, thereby altering the average current through the LEDs 2. A desired duty cycle may therefore be employed to provide a desired brightness, e.g. by varying the pulse widths and/or their frequency, whilst working within suitable limits for the device. Typically, LEDs are rated at an average maximum current of 10-20 mA. They can be driven harder, but this tends to reduce their working life, and generally LEDs should be driven at less than their maximum rating.

The LED display 1 may be configured with any number of rows. However, in practice, there is a limit due to the available driver current and the duty cycle. Some displays may use only one row, in which case no row driver 4 is required, and the row is permanently grounded. Typically, a display will use two to four rows (or more) that are arranged in a serpentine manner along the length of a display. Thus, when four array rows are used in a display, the first, fifth and ninth pixel rows as seen by a user of the display will comprise a single continuous row of the actual LED array. The addressable pixels of the LED array may comprise merely a single

LED 2. It is possible, however, for each pixel to comprise more than one LED, e.g. LEDs 2a and 2b. The LEDs 2a,2b thus form a cluster of LEDs that are not individually addressable, but are lit together. Although LEDs 2a,2b are shown in parallel, the LEDs of a cluster could be in series, in parallel or both. The microcontroller 3 controls all of the functions within the LED display

1 , including communications with a controlling PC or the like, the production of default messages, scanning rates, the reading of temperature sensors and the like.

The above is standard LED control and would be well understood by a man skilled in the art.

Referring to Fig. 2, an LED display in accordance with the present invention is similar to that of Fig. 1 , but further includes monitoring circuitry 6 for determining the condition of the various LEDs 2. Monitoring circuitry 6 includes a sensor 7 (a resistive element) in each of the row lines RowrRow_n. These sensors 7 are located between the LEDs 2 of a row and their common ground so as to provide a parallel circuit to ground with the row switches RowrRow_n. The monitoring circuitry 6 also includes an analogue to digital (A/D) converter 8 for each row Row Row_n to monitor the voltage across the associated sensor 7.

Importantly in this embodiment, the monitoring circuitry 6 further includes a switch TSι-TS_n for each row sensor 7 to switch the sensor 7 into and out of the row circuitry.

These sensor switches TS-ι-TS_n may take the form of e.g. MOS-FET transistors, and are activated by the microcontroller 3 in a similar manner to the row sink switches DSrDS_n.

Alternatively, the switches TSrTS_n may take the form of input/output ports of the microprocessor 3. These ports would then be raised to a high level to effectively switch the sensor 7 out of the row circuitry, and placed in a low level condition to switch the sensor 7 into the row circuitry.

The microcontroller 3 can thus operate any of the rows of the LED array in either an illumination mode or in a test mode. In the illumination mode, the microprocessor 3 closes the sink switch

DSi-DS_n for a row, opens the sensor switch TS TS_n for that row, and activates the column driver 5 to apply a voltage to those LEDs 2 of the row which need to be illuminated to provide a desired display element. This mode is therefore similar to a standard LCD display illumination control, and the rows of the array may be operated so as to provide e.g. a 25 frames per second (or more) display rate that will appear constant to an observer.

In the test mode of a row, the row sink-switch DSι-DS_n is opened and the row sensor switch TSrTS_n is closed. This effectively places the row sensor 7 (resistance element) into series with the LEDs 2 of the row, between the LEDs 2 and their common sink, e.g. ground, and allows the current flowing through the LEDs 2 of the row to be monitored through the voltage across the sensor resistor 7, as monitored by the A/D converters 8.

The sensors 7 may e.g. have a resistance of 50 ohms or greater. For example, assuming that a current of about 20 mA is drawn, then a sensor with a 100 ohm resistance will provide a voltage drop of about 2V, which can be effectively monitored by the A/D converters 8.

When in the test mode, the microcontroller 3 may instruct the column driver 5 to activate the LEDs 2 one at a time, so that the current drawn by each LED 2 (or cluster of LEDs 2a,2b) may be individually monitored. It may also operate the LED components in groups, each group being operated one at a time.

The test mode may be carried out on a row at any time that that row is not in the illumination mode. Where the display is flashed, e.g. 25 times per second, the test mode may be activated between each flashed frame or any pair of them. The LEDs 2 may however be tested at any suitable time, in a random or sequential manner, and one row could be tested whilst another is in the illumination mode.

The microcontroller 3 receives the information from the A/D converters 8, and may use it as desired. Thus, it may simply pass the information to a central control, may analyse the data and send the results of the analysis to a central control, and/or may act on the data itself.

The data may be analysed to determine whether a fault condition exists, e.g. because the monitored current has deviated from a set point value, e.g. due to an open or short circuit or the like caused by a LED. A change in current would also occur for example when one or more LEDs of a LED cluster where faulty. Fault results from a number of the individual LED components (or groups of LED components) tested may be correlated to check for other faults, e.g. in the row or column drivers, the power supply or the like. Also or alternatively, the results of the monitoring may be stored in a memory 9 of the display device or may be passed to the central control for storage. The invention can thus keep a log of the statuses of the LEDs 2. This may be useful for example should someone try to argue that the sign was defective in some manner at a particular time. The log may record actual currents drawn by the LEDs 2 or merely that a LED was determined to be working correctly or not. The latter uses less storage space, as the status may be recorded as a "1" or a "0" bit, whilst the former may provide more information as to the fault. The test mode may be made in relation to all of the LEDs 2, or only in relation to the LEDs 2 that are required to be illuminated to generate a desired sign.

In the latter case, the information obtained is still enough to show that a display is or was displaying the correct sign to e.g. a vehicle driver, whilst reducing the amount of space required to store or transmit the data. This assumes that only those LED components required to be illuminated are in fact illuminated (e.g. none are illuminated because of a defective driver or the like).

If an unwanted LED component is illuminated, then this may be picked up in the standard test mode (i.e. when detecting whether the desired LED components are illuminated), e.g. through an unexpected current value in a row circuit including the unwanted LED illumination. This may however not always be possible e.g. due to a lack of sensitivity of a monitoring circuit. In this case, a further test for unwanted LED component illuminations may be required. This may be implemented by testing for illuminated LED components (i.e. current flow through the sensors 7), whilst activating none of the LED components, e.g. by setting all of the column driver outputs low.

Fig. 3 shows a second embodiment of the present invention, which is similar to that of the first embodiment of Fig. 2, but provides the test switches TSrTS_n so that they are in series with the row switches Row Row_n. This then requires the sensors 7 to be in parallel with the test switches TS TS_n.

The embodiment of Fig. 3 works in the same manner as the embodiment of Fig. 2, except that when a row is to be tested, the test switch TSrTS_n is open and the row switch RowrRow_n is closed, whilst when a row is in an illumination mode, then both the test switch TSrTS_n and the row switch Row Row_n are closed.

This embodiment has the advantage that it can record a fault if a row switch or the row driver is faulty, whilst this may not be possible in the parallel configuration of Fig. 2. - The device 1 may be used in a stand-alone manner. Alternatively, it may form part of a larger system in which e.g. a number of such displays communicate with a central control.

Fig. 4 shows a third embodiment of the present invention, which is similar to the second embodiment of Fig. 3, but in which the monitoring circuitry 6 has been reduced to the use of only a single monitoring sensor 7, switch TS1 and A/D converter 8. If switch TS1 is open, then the sensor 7 is switched into the array circuitry, and the current can be monitored for whichever of the rows has its row switch DSrDS_n closed. A similar modification can be carried out in respect of the first embodiment of Fig. 2, so that only one sensor 7, switch TSi, and A/D converter need be used.

Fig. 5 shows an overall LED display system 10 in which a number of LED displays 1 are connected to a central control 11. Each LED display 1 includes an array of LEDs 2 and a microcontroller 3 that communicate with and receives instruction from a central control 11 including suitable processing means 12 and memory means 13.

The central control 11 will instruct a display 1 as to an image to display, and the microcontroller 3 will activate the appropriate LEDs 2 accordingly. The microcontrollers 3 will also monitor the condition of the various LEDs 2, and will forward the results to the central control 11 , which will then process the results and store them in the memory means 13.

If a fault is detected, then the central control 13 may take any suitable action. For example, it may dispatch a repair team to fix the display, it may disable the display, it may instruct the display to display a default sign, or it may attempt to alter the sign to be displayed, so that it may still be displayed without using the faulty LEDs 2, e.g. by shifting the graphic or the like a pixel to the side, or by activating adjacent pixels or the like.

These actions could also be taken by the microcontrollers 3 themselves. Communication between the displays 1 and central control 11 may take place in any suitable manner, and the central control 11 may poll the displays 1 , or the displays 1 may communicate at set times or when a notifiable event occurs, such as a failure.

The results of the monitoring may be stored in the individual displays 1 , or may be stored in the central memory 13 within the central control 11. The results may be used in any suitable manner.

The LED displays and system discussed above could be used in many different situations, and could take many different forms. For example, the displays 1 could be ticker or moving message displays in a building or other area, and could be controlled and monitored by a central control 11 that sends message information to each. It is especially applicable to road signs and the like, where the correct display of information is critical to safety.

As well as providing a display, the LEDs 2 may also provide illumination, e.g. the lights of a traffic signal.

It is to be understood that various alterations, additions and/or modifications may be made to the parts previously described without departing from the ambit of the present invention, and that for example, in the light of the teachings of the present invention, the features of the invention may be implemented in software, firmware and/or hardware in a variety of manners as would be understood by the skilled man, and the various components may take on different e.g. resistive values and the like dependent on the particular situations in which the invention is applied.

For example, in an alternative embodiment, the sensor 7 (resistive element) could be permanently connected between the LEDs 2 of a row and their common sink, without needing the test switches, and the LEDs 2 in a row could be operated individually or in small groups in both an illumination mode and/or in a test mode.

The invention need not relate only to LEDs, but has wider applications, e.g. in any situation involving a number of low voltage components in an array that must be monitored individually.

Although the invention has used monitoring sensors in the row circuits, it could also use monitoring sensors in the column circuits.

Claims

1. An LED device having an array of LED components, the device including circuitry for illuminating the LED components and circuitry for monitoring the current drawn by individual LED components or groups of LED components within the array.

2. The device of claim 1 , wherein the device is operated in an illumination mode so that only one LED component or one group of LED components in a row or column is switched on at any one time.

3. The device of claim 1 , wherein the device operates in an illumination mode and in a test mode, wherein in the test mode only one LED component or one group of LED components on a row or column are lit at a time.

4. The device of claim 1 , 2 or 3, wherein the monitoring circuitry includes one or more monitoring sensors for monitoring each row or column of LED components in the array.

5. The device of claim 4, wherein the monitoring sensor is a resistive element, whose voltage drop is monitored.

6. The device of claim 5, wherein the resistive element is placed between the LED components of a row or column and a common ground.

7. The device of any preceding claim, wherein the monitoring circuitry includes sensing circuitry that can be switched into and out of the array circuitry.

8. The device of claim 7, wherein the sensing circuitry is in parallel with a row or column driving circuit of the array.

9. The device of claim 7 or 8, wherein switching circuitry for switching the sensing circuitry includes input/output ports of a microprocessor.

10. The device of claim 7, wherein the sensing circuitry is in series with a row or column driving circuit of the array.

11. The device of claim 7, 8 or 9, wherein switching circuitry for switching the sensing circuitry includes a transistor component.

12. The device of any of claims 4 to 11 , wherein the device is operated in an illumination manner by activating multiple LED components simultaneously per row or column, and wherein the device is operated in a test mode by switching sensing circuitry into the illumination circuitry when a test is to be conducted.

13. The device of any of claims 4 to 12, wherein the monitoring circuitry includes means for monitoring the voltage across the monitoring sensor.

14. The device of claim 13, wherein the voltage across the monitoring sensor is monitored by an analogue to digital (A/D) converter that outputs a signal proportional to the voltage across the sensor.

15. The device of any preceding claim, wherein data obtained from the monitoring circuitry is logged.

16. The device of any preceding claim, wherein data obtained from the monitoring circuitry is passed to a central control with which the device communicates.

17. The device of any preceding claim, wherein data obtained from the monitoring circuit is compared to one or more threshold values to determine whether a LED component is faulty.

18. The device of any preceding claim, wherein the amount of current passing through a LED component is determined.

19. The device of any preceding claim, wherein the monitoring results for a plurality of LED components are correlated with one another in order to identify problems in the device.

20. The device of any preceding claim, wherein the monitoring circuitry monitors all of the LED components of the array.

21. The device of any of claims 1 to 19, wherein the monitoring circuitry monitors a subset of all of the LED components of the array.

22. The device of claim 21 , wherein the monitoring circuitry monitors only those LED components of the array that are required to be illuminated.

23. An LED device including an array of LED components, means for monitoring a condition of the separate LED components, and means for logging the monitored conditions.

24. An LED device including an array of LED components, means for determining which of the LED components are required to be illuminated, and means for monitoring the condition of the LED components that are required to be illuminated.

25. An LED device including an array of LED components, means for operating the LED components in an illumination mode, and means for operating the LED components in a test mode in which LED components of any one row or column of the array are individually illuminated.

26. An LED device including an array of LED components, means for illuminating the LED components, and means for monitoring the condition of the LED components, wherein the means for monitoring the LED components includes means for switching a sensor into a row or column of the array for testing purposes.

27. An LED device system including a remote central control and one or more LED devices in accordance with any preceding claim.

28. An LED device system including a central control and one or more remote LED array devices, each LED array device including an array of LED components, means for receiving illumination instructions from the central control, means for illuminating the LED components of the array in accordance with the illumination instructions, means for testing the condition of the LED components, and means for communicating information to the central control relating to the results of the test.

29. An LED device control system including one or more LED devices, each having an array of LED components, and a remote central control for controlling the one or more devices, wherein each device includes means for detecting a condition of the array components, and means for sending information to the central control relating to the detected conditions.

30. An electronically-activated array including a plurality of components connected together in a row and column formation to form the array, the components being actuated by an electrical current supplied by one or more array drivers, wherein the array includes a monitoring circuit for monitoring the current drawn by individual array components or groups of components.

31. The array of claim 30, wherein the monitoring circuit includes a current sensor in each of the rows or columns of the array.

32. The array of claim 30 or 31 , wherein the monitoring circuit includes a sensing means that is switchable into and out of a row or column circuit of the array, the sensing means being switched out of the circuit when the row or column is not under test.

33. A device including an array of electronically-activated components, means for monitoring a condition of the separate components, and means for logging the monitored conditions.

34. A device including an array of electronically-activated components, means for determining which of the components are required to be activated, and means for monitoring the condition of the components that are required to be activated.

35. A device including an array of electronically-activated components, means for operating the components in an activation mode, and means for operating the components in a test mode in which components of any one row or column of the array are individually activated.

36. A device including an array of electronically-activated components, means for illuminating the components, and means for monitoring the condition of the components, wherein the means for monitoring the components includes means for switching a sensor into a row or column of the array for testing purposes.

37. A device system including a remote central control and one or more devices in accordance with any of claims 33 to 36.

38. A device system including a central control and one or more remote electronically-activated array devices, each array device including an array of electronically-activated components, means for receiving activation instructions from the central control, means for activating the components of the array in accordance with the activation instructions, means for testing the condition of the components, and means for communicating information to the central control relating to the results of the test.

39. A device control system including one or more electronically- activated devices, each having an array of electronically-activated components, and a remote central control for controlling the one or more devices, wherein each device includes means for detecting a condition of the array components, and means for sending information to the central control relating to the detected conditions.