WO2025174369A1

WO2025174369A1 - Power wire signaling for color control of emergency vehicle warning lights

Info

Publication number: WO2025174369A1
Application number: PCT/US2024/015876
Authority: WO
Inventors: Kevin Brewster
Original assignee: Electronic Controls Co
Current assignee: Electronic Controls Co
Priority date: 2024-02-14
Filing date: 2024-02-14
Publication date: 2025-08-21
Anticipated expiration: 2026-08-14
Also published as: WO2025174369A9

Abstract

An emergency vehicle warning lighting system generates a multi-color flash pattern. The system includes a multi-color emergency warning light having a first LED to produce the first illumination color, a second LED to produce the second illumination color, and light circuitry to control power applied to the first and second illumination colors, the multi-color emergency warning light having an electrical input configured to receive an input power signal, the input power signal providing electrical power and a color-change information signal to trigger a change between the first and second illumination colors according to the multi-color flash pattern; and flash pattern controller circuitry configured to generate the color-change information signal by including in the input power signal a color-change pulse period that is less than a configured PWM dimming pulse period.

Description

POWER WIRE SIGNALING FOR COLOR CONTROL OF EMERGENCY VEHICLE

WARNING LIGHTS

BACKGROUND INFORMATION

[0001] Many emergency vehicle warning systems use rooftop-mounted devices for 360-degree signal coverage. They also feature numerous other warning lights that emit light in a narrower direction and are mounted to various parts of the vehicle, such as the body, bumpers, fenders, doors, and windows. These other lights are commonly known as directional lights or simply directionals. Some directional lights emit a single color, while others, known as multi-color directional lights, can emit more than one color.

[0002] There are two broad categories of controlling the color and flashing behavior of directional lights: those with internally controlled flash patterns and those with externally controlled flash patterns.

Internal Flash Patterns

[0003] Directional lights in emergency vehicles often contain pre-programmed flash patterns. During the installation process, technicians can select a specific flash pattern for each light using a designated flash pattern selection wire. Once set, the directional light memorizes this pattern and displays it when powered. In multi-color directional lights, these patterns can include a combination of colors, such as alternating red and blue flashes.

[0004] A notable challenge in installing these systems is the need for extensive pre-configuration to ensure that all directional lights are set to the desired flash patterns. Additionally, installation requires managing numerous wires required for full functionality. The wiring for these directional lights is typically complex, involving several connections to accommodate various flash patterns, colors, and light intensities.

[0005] For instance, emergency warning systems often feature multiple operating modes, necessitating distinct flash patterns for different scenarios. This requirement leads to the inclusion of several power wires in many directional lights, each activating a unique flash pattern. A directional light combining red, blue, and white colors, mounted on an emergency vehicle's front bumper, would require multiple connections: a power wire for the primary red/blue flashing mode, another for a secondary flashing mode, a third for the white flashing mode, and a fourth for steady white illumination.

[0006] Additionally, these lights include a synchronization wire for coordinated flashing with other directionals. When connected among various lights, it ensures that they flash in unison. For effective synchronization, all connected lights need to be preconfigured to either the same flash pattern or ones with compatible timings. [0007] Other wire connections include a dim wire to adjust brightness (especially useful at night), a configuration wire for initial setup, and a ground wire.

External Flash Patterns

[0008] To mitigate the installation challenges of internal flash patterns and synchronization, directionals are sometimes set to a non-flashing steady-on mode, emitting constant light. In this case, a separate flash-pattern control unit switches power on and off to create the flashing effect. The flash patterns for all directionals are contained within this controller, rather than in the individual lights. The control unit can create the desired flash patterns by switching the appropriate power wires on and off as required. This removes the need for the configuration and synchronization wires. High speed pulse-width-modulation of the power wires can be used to adjust the output light intensity, eliminating the need for the dim wire.

[0009] If the flashing of the directional light is controlled by a separate control unit rather than by the directional light itself, then the wiring to each directional can be simplified as follows: power wire for red; power wire for blue; power wire for white; and ground. Nevertheless, controlling the color of multi-color directional lights still requires multiple power wires from the flash pattern controller to each light.

Installation difficulties here stem from managing the numerous wires and ensuring the correct connection of different color power wires to the appropriate outputs on the flash pattern controller.

[0010] The flash pattern controller must also have multiple outputs for each emergency light or group of lights. Each output has to be able to provide enough power for the connected emergency light(s); they are power outputs, not just control signals. This reduces the number of emergency lights that can be controlled by a given controller.

SUMMARY OF THE DISCLOSURE [0011] This disclosure introduces an innovative technique for altering the active color or mode of operation of emergency vehicle warning lights. It achieves this by using the same wire that powers the warning light to also signal color changes. This signaling could involve brief power supply interruptions to encode the desired color or operational mode.

[0012] The described techniques allow for multi-color directional lights to be controlled by a single power wire (plus a ground return path, which may be a ground wire or through the body of the directional). This reduces the number of wires required and reduces the potential for wiring errors during installation. The flashing and dimming of the directional is managed by a separate control unit. But instead of using a separate power or control wire for each color, the color related information is sent to the directional by modulating the power supply to the directional.

[0013] Modulation may involve brief, coded power interruptions, changes in supply voltage, or sustained voltage alterations. In one embodiment, short sequences of about 1-10 ms interruptions to the device power are used to select color. The sequences are chosen such that they are clearly differentiable from the normal PWM signal used for dimming.

[0014] An advantage of this technique is its simplicity, both in terms of development and installation. For instance, some embodiments may be implemented primarily in firmware, with relatively minor hardware changes or extra electronics in either the controller or the light. These changes, therefore, can be used to upgrade or retrofit existing switch nodes and related products with a firmware update and no hardware changes. It also significantly simplifies the installation and configuration process for multi-color directional lights by reducing the need for multiple wiring. Color or mode selection is managed by modulating the power supply to the directional light, whether it is a single unit or multiple units connected to the same power source. This approach employs a single power wire, regardless of the number of colors the directional light can display.

[0015] This streamlined method offers several benefits:

1. Reduction in wiring: It minimizes the amount of wiring required, making the installation process more efficient.

2. Elimination of miswiring risks: By using a single power wire, it eliminates the potential for miswiring that can occur with multiple color-selection wires. 3. Simplified installation: It removes the need for pre-selecting flash patterns or colors during installation, ensuring all available colors of a directional light are usable.

4. Versatility: It allows for the utilization of all colors in a directional light, including those not initially planned for use, as it does not depend on additional wires that might be left out during installation.

[0016] In one aspect, an emergency vehicle warning lighting system is configured to generate a multi-color flash pattern. The multi-color flash pattern has a first illumination color followed by a second illumination color that is different from the first illumination color. The emergency vehicle lighting system includes a multi-color emergency warning light having a first LED to produce the first illumination color, a second LED to produce the second illumination color, and light circuitry to control power applied to the first and second illumination colors. The multi-color emergency warning light has an electrical input configured to receive an input power signal. The input power signal provides electrical power and a color-change information signal to trigger a change between the first and second illumination colors according to the multi-color flash pattern. Flash pattern controller circuitry is configured to generate the color-change information signal by including in the input power signal a colorchange pulse period that is less than a configured PWM dimming pulse period. The emergency vehicle warning lighting system may also include the input power signal providing the electrical power being a PWM signal. The emergency vehicle warning lighting system may also include the input power signal providing the electrical power being a steady-on signal. The emergency vehicle warning lighting system may also include the flash pattern controller circuitry included in a siren amplifier. The emergency vehicle warning lighting system may also include the multi-color emergency warning light being a directional light. The emergency vehicle warning lighting system may also include the multi-color emergency warning light being a multi-directional beacon. The emergency vehicle warning lighting system may also include durations of the color-change pulse period corresponding to color selections from among a group of colors. The emergency vehicle warning lighting system may also include the durations having a first duration corresponding to the first illumination color, and a second duration that is longer than the first duration corresponding to the second illumination color. The emergency vehicle warning lighting system may also include the color-change pulse period corresponding to an incremental change in illumination color selection that is incremented according to a sequence of available illumination colors. The emergency vehicle warning lighting system may also include a capacitor sized to maintain power to at least a portion of the light circuity while electrical power is not supplied during a blank time in the multi-color flash pattern. The emergency vehicle warning lighting system may also include the color-change information signal having a first color-change pulse period and a redundant color-change pulse period. Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims. [0017] In one aspect, a multi-color emergency warning light for an emergency vehicle warning lighting system configured to generate a multi-color flash pattern, the multi-color flash pattern having a first illumination color followed by a second illumination color that is different from the first illumination color, the multi-color emergency warning light includes a first LED to produce the first illumination color, a second LED to produce the second illumination color, an electrical input configured to receive an input power signal, the input power signal providing electrical power and a color-change information signal to trigger a change between the first and second illumination colors according to the multi-color flash pattern, and circuitry to detect the color-change information signal based on a color-change pulse period that is differentiable from a configured PWM dimming pulse period.

[0018] In one aspect, a method of changing an illumination color in a multi-color emergency warning light for an emergency vehicle warning lighting system, the method includes receiving an input power signal, the input power signal providing electrical power and a color-change information signal to trigger a change between first and second illumination colors, detecting the color-change information signal based on a color-change pulse period that is differentiable from a configured PWM dimming pulse period, and triggering a change in the illumination color according to a relative position of edges temporally spaced apart by the color-change pulse period. The method may also include the input power signal providing the electrical power being a PWM signal. The method may also include the input power signal providing the electrical power being a steady-on signal. The method may also include the multi-color emergency warning light being a directional light. The method may also include the multi-color emergency warning light being a multidirectional beacon. The method may also include durations of the color-change pulse period corresponding to color selections from among a group of colors. The method may also include the durations having a first duration corresponding to the first illumination color, and a second duration that is longer than the first duration corresponding to the second illumination color. The method may also include the color-change pulse period corresponding to an incremental change in illumination color selection according to a sequence of available illumination colors. The method may also include maintaining (e.g., with a capacitor) power to at least a portion of the light circuity while power is not supplied during a blank time in a multi-color flash pattern. The method may also include the color-change information signal having a first color-change pulse period and a redundant color-change pulse period. Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.

[0019] Additional aspects and advantages will be apparent from the following detailed description of embodiments, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0020] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0021] FIG. 1 is a pictorial view of an emergency vehicle in accordance with one embodiment.

[0022] FIG. 2 is a block diagram of an emergency warning vehicle lighting system in accordance with one embodiment.

[0023] FIG. 3 is a schematic and block diagram of an emergency vehicle lighting system in accordance with one embodiment.

[0024] FIG. 4 is a timing diagram showing a color change to red during 50% PWM power signal in accordance with one embodiment.

[0025] FIG. 5 is a timing diagram showing a color change to blue during 90% PWM power signal in accordance with one embodiment.

[0026] FIG. 6 is a timing diagram showing a color change to amber during a steady-on power signal in accordance with one embodiment.

[0027] FIG. 7 is a timing diagram showing a color change to white during a start up in accordance with one embodiment.

[0028] FIG. 8 is a timing diagram showing a quad-flash flash pattern in accordance with one embodiment. [0029] FIG. 9 is a pictorial view of a trace diagram in accordance with one embodiment.

[0030] FIG. 10 is a pictorial view of a trace diagram in accordance with one embodiment.

[0031] FIG. 11 is a flow diagram of a process of changing an illumination color in a multi-color emergency warning light for an emergency vehicle warning lighting system in accordance with one embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0032] FIG. 1 shows an emergency vehicle 100 including emergency vehicle warning lighting system 102. Emergency vehicle warning lighting system 102 includes directional warning lights 104, a light bar 106, optional beacon (not shown), and a flash pattern controller 108. As explained below, flash pattern controller 108 is configured to trigger a multi-color flash pattern, i.e., a first illumination color followed by a second illumination color that is different from the first illumination color.

[0033] FIG. 2 is a block diagram of emergency vehicle warning lighting system 102, showing multi-color emergency warning lights 202 electrically coupled to flash pattern controller 108. Flash pattern controller 108 may be implemented as a switch node (model number PCM12-XXXXX), siren amplifier module (model number CS82- XXXXX), junction box (model number JBOX-XXXXX-C), or the like available from Code 3, Inc of St. Louis, Missouri.

[0034] An upper set 204 of four multi-color emergency warning light 202 has each light separately connected to flash pattern controller 108 using an individual power wire 206. In contrast, a lower set 208 of four multi-color emergency warning light 202 have a first pair 210 connected in parallel using a power wire 212. A second pair 214 are connection in parallel using a power wire 216.

[0035] Each power wire 206, 212, and 216 may switch on and off independently and/or in coordination with each other to flash multi-color emergency warning light 202 according to a flash pattern signal. PWM dimming is also signaled from flash pattern controller 108, although in some embodiments PWM dimming may be implemented internally to each multi-color emergency warning light 202 (e.g., for thermal self-protection). [0036] FIG. 3 shows a portion of emergency vehicle warning lighting system 102 including flash pattern controller 108 and multi-color emergency warning light 202. [0037] In terms of inputs, flash pattern controller 108 is electrically coupled to a DC power source 302, which is commonly in a range of about 10V to about 30V, but may be up to 50V. Flash pattern controller 108 also includes a signal input 304 through which it receives commands provided though physical switches (not shown) or other electronic devices (not shown) or a network-type of connection such as CAN-bus (not shown).

[0038] Flash pattern controller 108 includes internal controller circuitry 306 such as one or more (i.e. , 4, 8, 12, or 16) electronic switches 308 controlled by a microcontroller 310 executing embedded firmware 312. An example microcontroller 310 is a PIC microcontroller. In other embodiments, such as in the switch node, microcontroller 310 is a 32-bit Cortex-M based microcontroller, but other options are also possible. Microcontroller 310 has programmable I/O ports acting as controls for electronic switches 308. In some embodiments, electronic switches 308 are so- called ProFET high-side switches in the Switch Node because they are rugged and reliable and include a lot of internal protection circuitry, but any transistor or FET with suitable ratings could be used. Electronic switches 308 are controlled to switch on and off independently from each other or in coordination with each other to flash emergency vehicle warning lighting system 102.

[0039] In the example of FIG. 3, the output from one embedded firmware 312 provides power over a power wire 300 to multi-color emergency warning light 202. Flash pattern controller 108 also communicates color-change information to multicolor emergency warning light 202 (or multiple emergency warning lights), by means of power wire 300.

[0040] Flash pattern controller 108 varies the power supplied to multi-color emergency warning light 202, and thus its optical output intensity, by rapidly switching electronic switches 308 on and off, to create a pulse-width modulation (PWM) signal on power wire 300. A typical PWM frequency is 100Hz. Using a 100Hz PWM frequency, there is 10 ms between the rising edges of each PWM cycle (above the threshold of visually noticeable flicker).

[0041] To signal a color for multi-color emergency warning light 202, flash pattern controller 108 rapidly switches power off and on to create rising edges that are closer than 10 ms. These edges are detected by multi-color emergency warning light 202 that differentiates them from the nominal PWM signal to establish the desired color. This is referred to as pulse-position detection in color-change information signals. Additional examples are provided below.

[0042] For completeness, FIG. 3 also shows an example of light circuitry 314 in multi-color emergency warning light 202, which may be a directional light, beacon light, or other type of emergency warning light. Light circuitry 314 includes an electrical input 316, a pull-down resistor 318, a reverse polarity protection diode 320, a current regulator 322, a voltage regulator 324, a protection circuit 326, an energy reservoir capacitor 328, a microcontroller 330, color switching circuitry 332, a first color LED 334, a second color LED 336, a third color LED 342, a fourth color LED 344, an optical beam-forming component (optic) 338, and an LED emission flash pattern 340.

[0043] Color switching circuitry 332 is a simplified diagram of a design that uses four separate current regulators (one for each LED color group) with enable pins that microcontroller 330 uses to switch them on and off, individually. In another example color switching circuitry 332 is a high-current analog demultiplexer or any suitable circuit that microcontroller 330 is able to control the current routed to different LED strings, i.e. , to select different colors.

[0044] The photometric radiation from the LEDs (LED emission flash pattern 340) is typically focused by optical beam-forming component (optic) 338, which is a lens, a reflector, a diffractive optic, or some combination of such parts.

[0045] The LEDs are powered by current regulator 322 or a number of such current regular circuits, and the desired color LED or group of LEDs is selected by microcontroller 330. Microcontroller 330 may switch the output of the current regular to the desired LEDs, or it may switch one or many current regulators on or off directly.

[0046] Microcontroller 330 is powered from energy reservoir capacitor 328 which is energized by voltage regulator 324. Voltage regulator 324 includes components which prevent the flow of energy from energy reservoir capacitor 328 to current regulator 322 and LEDs.

[0047] When the associated electronic switch 308 in flash pattern controller 108 activates, power flows through power wire 300 connecting flash pattern controller 108 to multi-color emergency warning light 202. [0048] Power then flows through reverse polarity protection diode 320, through voltage regulator 324, charging energy reservoir capacitor 328 and powering microcontroller 330.

[0049] When an electronic switch 308 turns off, microcontroller 330 continues to be powered for a short time (up to 100 ms) by energy in energy reservoir capacitor 328. During this time, microcontroller 330 is able to sense that power has been turned off by monitoring the voltage on power wire 300 through a protection circuit 326. Energy reservoir capacitor 328 provides power to microcontroller 330 during power-signal-resumption dead-time (explained later with reference to FIG. 4), PWM low periods, color-change sequences, and flash-pattern off periods up to 100 ms. For example, typical flash patterns do commonly include gaps (off periods) of 50 ms, and sometimes 500 ms or more (particularly when a pattern may flash lights on one side of the vehicle, and then the other). Energy reservoir capacitor 328 is sized to keep microcontroller 330 powered for at least 100 ms, which allows it to both (a) remember the last assigned color, and (b) keep measuring rising edge periods to detect new color commands. The switch node firmware keeps track of how long its outputs have been off, and knows that if an output has been off for greater than 100 ms then it needs to resend a color sequence to the light when it next turns on, even if it is the same color that it was previously. In other embodiments, another energy storage devices such as a battery may also be employed to maintain power to microcontroller 330 during prolonged flash pattern off periods.

[0050] A pull-down resistor 318 ensures that the voltage on power wire 300 decays rapidly, so that microcontroller 330 can sense the loss of power within 1 millisecond. [0051] If power to multi-color emergency warning light 202 is reapplied before the energy in energy reservoir capacitor 328 has been exhausted, microcontrollers 330 will be able to measure the time that the power was disconnected for, and the time periods between subsequent rising edges on power wire 300. These measured time periods are used to select which color LEDs to energize, as shown in the following examples.

[0052] FIG. 4 shows an input power signal 400 including red color-change information signal 402 provided within a PWM signal 404. In this example, each configured PWM dimming pulse period 406 is 10 ms (tAB = tBC = tCG = tGI = I0 ms). Thus, in this example, microcontroller 330 (FIG. 3) of multi-color emergency warning light 202 would detect a rising edge for a PWM dimming pulse each 10 ms, and the pulse width is changed to brighten or dim LED emission flash pattern 340. The example shown in FIG. 4 is a 50% duty cycle for an intermediate brightness level, but other duty cycles are possible. The duty cycle of the PWM period can vary from 0% (always off, no pulse at all) to 100% (constant power, no off-time gap at all). Theoretically there are no limits on the duty cycle, although in practice the switch node may control this to a resolution of about 1 %. With a 1 % duty, the positive portion of the 100Hz PWM signal would be 1/100*10 ms = 100 ps wide. These numbers, however, are just examples for a chosen PWM frequency.

[0053] To signal a color change, a color-change pulse period 408 is triggered so that it is less than configured PWM dimming pulse period 406. Specifically, a first color-change rising edge 410 of a first color-change pulse 412 and a second colorchange rising edge 414 of a second color-change pulse 416 are generated so that color-change pulse period 408 between them is less than 10 ms. In this example, color-change pulse period 408 is 2 ms (tDE = 2 ms).

[0054] In some embodiments, a start of a color-change sequence at tC is temporally aligned with start of PWM new cycle. A I ms low is maintained (i.e. , colorchange signal delay 418) to ensure first color-change rising edge 410 is generated at tD. Although technically unnecessary in this example FIG. 4, color-change signal delay 418 is employed for steady-on signals, as explained later with reference to FIG. 6.

[0055] In the present example, durations for color-change pulse period 408 represent the desired color selection, e.g., temporally spaced leading edges such as 2 ms (500 Hz) that represents red, 3 ms represents blue (FIG. 5), 4 ms represents amber (FIG. 6), and 5 ms represents white (FIG. 7). Skilled persons will appreciate, however, that the specific times for durations may be different, depending on configured PWM dimming pulse periods 406 and the minimum low pulse width (which is 1 ms, in the present example). In other embodiments, the duration is fixed, and colors are cycled through (e.g., incrementally changed) according to a sequence.

[0056] In some embodiments, a switch node could sometimes generate spurious rising edges when changing the PWM duty cycle mid PWM cycle, and these edges could be less than 10 ms apart, which could potentially trigger incorrect color changes. As part of the firmware changes to the switch node implementation, changes to the PWM generation behavior were made so that these spurious edges could no longer occur. Furthermore, a light presents a low impedance on the power wire, which itself is usually sufficient to prevent spurious spikes due to general electrical noise and interference. There is also some filtering in protection circuit 326 and pull-down resistor 318.

[0057] FIG. 4 also shows an example of a redundant color-change pulse period 420 (tEF = 2 ms). In the present example, microcontroller 330 changes color in response to a single instance of color-change pulse period 408 being less than 10 ms, in which case a third color-change rising edge 422 of a third color-change pulse 424 could be optionally omitted.

[0058] Redundant color-change pulse period 420, however, has an advantage when starting up from an initially unpowered state. In this situation, multi-color emergency warning light 202 is provided a short initialization period before it is capable of accurately measuring the time interval between rising edges on power wire 300. Thus, microcontroller 330 cannot accurately measure color-change pulse period 408 from first color-change rising edge 410 to second color-change rising edge 414. But after being powered up and initializing itself during the first 1 ms pulse, microcontroller 330 correctly measures redundant color-change pulse period 420 from second color-change rising edge 414 to third color-change rising edge 422. This situation is shown in FIG. 7.

[0059] After redundant color-change pulse period 420, to avoid an inadvertent color selection, there is a power signal resumption dead-time 426 (tFH = 10 ms). Power signal resumption dead-time 426 ensures there is no other rising edge for at least 10 ms after third color-change rising edge 422. Thus, power signal resumption dead-time 426 is inserted into the color change sequence after third color-change pulse 424 at tF, such that tFH = 10 ms.

[0060] After power signal resumption dead-time 426, the next rising edge occurs at the start of the next PWM cycle, at time tl. If this power signal resumption dead-time 426 were not enforced, the next rising-edge after tF would occur at time tG, which is only 5 ms after tF, which would change the color to white. Thus, with power signal resumption dead-time 426, there are no timing glitches that would otherwise introduce rising edges closer than 10 ms, which could be misinterpreted as color change requests. In some other embodiments, the PWM timing may also be advanced from tl to tH, but in practice, due to hardware and firmware limitations (i.e. , all twelve outputs on a switch node have synchronous PWM cycle periods, meaning all PWM periods 406 are aligned), the first PWM cycle would typically not follow the dead-time at an arbitrary time; it will start at the same time as for all the other outputs, some multiple of 10 ms after it was interrupted by the color-change sequence.

[0061] FIG. 5 shows an input power signal 500 including blue color-change information signal 502 provided within PWM signal 504, which is similar to PWM signal 404 but has a 90% duty (but still has configured PWM dimming pulse period 406). Blue color-change information signal 502 is similar to red color-change information signal 402 (FIG. 4), except color-change pulse period 408 is shown as 3 ms (e.g., for representing blue). Because color-change pulse period 408 is now 3 ms, tK occurs later than tF, and tL occurs later than tH. Thus, tl_l is less than tHI.

[0062] FIG. 6 shows an input power signal 600 including amber color-change information signal 604 provided within a steady-on signal 602. As noted previously, color-change pulse period 408 is 4 ms, and amber color-change information signal 604 is preceded by color-change signal delay 418 so that a rising edge can be triggered at tD. Amber color-change information signal 604 is then followed by power signal resumption dead-time 426.

[0063] FIG. 7 shows an input power signal 700 including white color-change information signal 704 provided before a steady-on signal 702 to set up a color change when microcontroller 330 is first powered up. In this example color-change pulse period 408 is 5 ms. During the I ms pulse of power at tP, microcontroller 330 powers up during color-change pulse period 408 and prepares to measure colorchange pulse period 420 (period tQR). The color is recognized at time tR. The start of steady-on signal 702 at tS commences immediately following power signal resumption dead-time 426.

[0064] In some embodiments, microcontroller 330 remembers a previously requested color for up to approximately 100 ms after power is removed. If power is removed for longer than this, then when microcontroller 330 is next powered up, the desired color is recommunicated to it. Also, as indicated previously, energy reservoir capacitor 328 helps avoid having to resend color information for every pulse in, e.g., a quad-flash pattern (see, e.g., FIG. 8).

[0065] FIG. 8 shows an example quad-flash flash pattern 802. Example pattern 802 entails 50 ms on (tAB = 50 ms) and then 50 ms off (tBC = 50 ms blank time), repeated four times (tAD = tDE = tEF = tFG = 400 ms). Because each color-change sequence 804 consumes about 20 ms, having to assign a color for every 50 ms pulse would reduce an amount of light emitted during each 50 ms on pulse.

[0066] Energy reservoir capacitor 328 keeps microcontroller 330 alive during each 50 ms “off” period throughout tAD, tEF, etc., but power (and thus color selection) is lost during the much longer 400 ms period tDE between quad-flashes. Thus, flash pattern controller 108 sends a color-change pulse (i.e. , one of color-change pulse periods 408, described previously) in a first 50 ms “on” period of each “quad flash,” i.e., at times tA, tE, and tG. For instance, at tA, color-change pulse period 408 may indicate red for the first 50 ms “on” period from tAB, which remains the color for each 50 ms “on” period throughout tAD. Likewise, at tE, color-change pulse period 408 may indicate blue for each 50 ms on period in tEF, and so forth. In other embodiments, each quad flash has the same color, so flash pattern controller 108 resends the same color information at the start of each quad flash.

[0067] FIG. 9 shows a longer time sample with three color change sequences. For example, the three sequences may form a flash pattern that includes red, blue, and red flashes in a sequence.

[0068] FIG. 10 shows a series of color-change pulse-sequences similar to FIG. 9, but with an otherwise steady power supply to the directional, rather than the 50% PWM signal.

[0069] FIG. 11 shows a process of changing an illumination color in a multi-color emergency warning light for an emergency vehicle warning lighting system. In block 1102, process 1100 receives an input power signal, the input power signal providing electrical power and a color-change information signal to trigger a change between first and second illumination colors according to a flash pattern. In block 1104, process 1100 detects the color-change information signal based on a color-change pulse period that is less than a configured PWM dimming pulse period. In block 1106, process 1100 triggers a change in the illumination color based on a duration of the color-change pulse period.

[0070] In other embodiments, color change information may be triggered based on timing between falling edges rather than rising edges. Timing of falling edges, however, are typically subject to parasitic capacitive time constants that vary depending on the system configuration. Likewise, color-change information may be included in pulse durations rather than in pulse periods, although these durations are subject to variation in decay rates and detection threshold of the fal ling/trailing pulse edges. They would also need to be differentiated from PWM drive signals (i.e. , a 2 ms color-selection pulse-width would have a similar duration as a 20% PWM drive signal.)

[0071] In light of this disclosure, skilled persons will appreciate that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by claims and equivalents.

Claims

CLAIMS What is claimed is:

1 . An emergency vehicle warning lighting system for generating a multi-color flash pattern, the multi-color flash pattern having a first illumination color followed by a second illumination color that is different from the first illumination color, the emergency vehicle lighting system comprising: a multi-color emergency warning light having a first LED to produce the first illumination color, a second LED to produce the second illumination color, and light circuitry to control power applied to the first and second illumination colors, the multi-color emergency warning light having an electrical input configured to receive an input power signal, the input power signal providing electrical power and a colorchange information signal to trigger a change between the first and second illumination colors according to the multi-color flash pattern; and flash pattern controller circuitry configured to generate the color-change information signal by including in the input power signal a color-change pulse period that is less than a configured PWM dimming pulse period.

2. The emergency vehicle warning lighting system of claim 1 , in which the input power signal providing the electrical power is a PWM signal.

3. The emergency vehicle warning lighting system of claim 1 , in which the input power signal providing the electrical power is a steady-on signal.

4. The emergency vehicle warning lighting system of claim 1 , in which the flash pattern controller circuitry is included in a siren amplifier.

5. The emergency vehicle warning lighting system of claim 1 , in which the multicolor emergency warning light is a directional light.

6. The emergency vehicle warning lighting system of claim 1 , in which the multicolor emergency warning light is a multi-directional beacon.

7. The emergency vehicle warning lighting system of claim 1 , in which durations of the color-change pulse period correspond to color selections from among a group of colors.

8. The emergency vehicle warning lighting system of claim 7, in which the durations include a first duration corresponding to the first illumination color, and a second duration that is longer than the first duration corresponding to the second illumination color.

9. The emergency vehicle warning lighting system of claim 1 , in which the colorchange pulse period corresponds to an incremental change in illumination color selection according to a sequence of available illumination colors.

10. The emergency vehicle warning lighting system of claim 1 , further comprising a capacitor sized to maintain power to at least a portion of the light circuity while electrical power is not supplied during a blank time in the multi-color flash pattern.

11 . The emergency vehicle warning lighting system of claim 1 , in which the colorchange information signal includes a first color-change pulse period and a redundant color-change pulse period.

12. A multi-color emergency warning light for an emergency vehicle warning lighting system configured to generate a multi-color flash pattern, the multi-color flash pattern having a first illumination color followed by a second illumination color that is different from the first illumination color, the multi-color emergency warning light comprising: a first LED to produce the first illumination color; a second LED to produce the second illumination color; an electrical input configured to receive an input power signal, the input power signal providing electrical power and a color-change information signal to trigger a change between the first and second illumination colors according to the multi-color flash pattern; and circuitry to detect the color-change information signal based on a colorchange pulse period that is differentiable from a configured PWM dimming pulse period.

13. The multi-color emergency warning light of claim 12, in which the input power signal providing the electrical power is a PWM signal.

14. The multi-color emergency warning light of claim 12, in which the input power signal providing the electrical power is a steady-on signal.

15. The multi-color emergency warning light of claim 12, comprising a directional light.

16. The multi-color emergency warning light of claim 12, comprising a multidirectional beacon.

17. The multi-color emergency warning light of claim 12, in which durations of the color-change pulse period correspond to color selections from among a group of colors.

18. The multi-color emergency warning light of claim 17, in which the durations include a first duration corresponding to the first illumination color, and a second duration that is longer than the first duration corresponding to the second illumination color.

19. The multi-color emergency warning light of claim 12, in which the color-change pulse period corresponds to an incremental change in illumination color selection according to a sequence of available illumination colors.

20. The multi-color emergency warning light of claim 12, further comprising a capacitor sized to maintain power to at least a portion of the light circuity while electrical power is not supplied during a blank time in the multi-color flash pattern.

21. A method of changing an illumination color in a multi-color emergency warning light for an emergency vehicle warning lighting system, the method comprising: receiving an input power signal, the input power signal providing electrical power and a color-change information signal to trigger a change between first and second illumination colors; detecting the color-change information signal based on a color-change pulse period that is differentiable from a configured PWM dimming pulse period; and triggering a change in the illumination color according to a relative position of edges temporally spaced apart by the color-change pulse period.

22. The method of claim 21 , in which the input power signal providing the electrical power is a PWM signal.

23. The method of claim 21 , in which the input power signal providing the electrical power is a steady-on signal.

24. The method of claim 21 , in which the multi-color emergency warning light is a directional light.

25. The method of claim 21 , in which the multi-color emergency warning light is a multi-directional beacon.

26. The method of claim 21 , in which durations of the color-change pulse period correspond to color selections from among a group of colors.

27. The method of claim 26, in which the durations include a first duration corresponding to the first illumination color, and a second duration that is longer than the first duration corresponding to the second illumination color.

28. The method of claim 21 , in which the color-change pulse period corresponds to an incremental change in illumination color selection according to a sequence of available illumination colors.

29. The method of claim 21 , further comprising maintaining power to at least a portion of the light circuity while power is not supplied during a blank time in a multicolor flash pattern.

30. The method of claim 21 , in which the color-change information signal includes a first color-change pulse period and a redundant color-change pulse period.