Tel: 905–690–4709 dk@tfwm.com - Darryl Kirkland, Publisher

Fade to Black: Wireless Dimming and Motion in Worship

Commercial wireless dimming systems use battery power and radio signals to remotely control lighting. With no dragging or unsightly wires for power or control, lamps can be placed just about anywhere. Some dimmers can also power motors, and effects. Most are controlled with DMX data, making it easy to integrate wireless lighting with a traditional wired lighting setup.

There are three main components to a wireless dimming system: a transmitter, a receiver, and a dimmer; in most cases, multiple receivers and dimmers are used. Unlike wireless DMX (which transmits one or more DMX universes from point A to point B) wireless dimming goes one step further and powers a load, like a lamp or motor. A vast array of 12VDC batteries and lamps are available, providing lighting designers with a large pallet of sizes, shapes, wattages, and beam angles. More recently, LED lamps and new battery types have further expanded the versatility of wireless dimming.

Operating range generally exceeds 200 ft. point to point; many systems are good beyond 300 ft. In an open indoor area, this translates to a useable area of 40,000 to over 100,000 square ft. Signals reflect off indoor surfaces, improving coverage.

To make the most of a wireless dimming system today, users should be familiar with the basic principles of radios, batteries, DC dimmers, and LEDs. Many people investigating wireless systems for the first time are most concerned about the reliability of the radio link; in fact, the area that demands careful consideration is battery charging and maintenance.
Hide It or Move It

Generally speaking, applications for wireless dimming fall into two broad categories: hidden placements, and mobile placements. In a house of worship, you may want a lamp somewhere other than the primary presentation area – somewhere that is not wired for control or power. If you are using slim-line or transparent furniture or displays, even light-gauge wiring can be unsightly and distracting; a wireless dimmer is the perfect solution.

Untethered mobile locations are very popular for wireless dimming. Wireless lamps placed within garments, on musical soloists, or even in the congregation, can help direct spectator attention. With no control or power wires, mobile items can enter, exit, and travel a complex or improvised path. Add wireless motion to remotely drive set pieces around your space – the safe and professional equivalent of a remote-control car. Wireless motion can also be used to drive winches and linear actuators, or trip solenoids. A wireless dimmer can even drive an ac inverter to provide 120VAC power, switched by a DMX channel, with no supply wired.

Wireless dimming is easy to apply in new ways at the spur of the moment – use it in today’s sermon to illuminate a prop, or cast an unusual shadow. Later the same day (or even the same presentation), use that same portable dimmer to highlight a soloist in a choir presentation. Easily placed, repositioned, or adjusted with only a moment’s notice, portable wireless lighting is exceptionally versatile. Controlled from the same lighting console that commands your fixed lighting, wireless lamps can be controlled, programmed, and cued just like wired DMX fixtures, with identical responsiveness and resolution.

Component vs. Integrated Systems
Several wireless dimming systems are available, each with unique advantages. Component systems typically consist of a wireless DMX link along with separate low-voltage dimmers. The City Theatrical WDS is such a system, broadcasting one DMX universe from the WDS Transmitter to any number of WDS Receivers. Individual dimmers are connected to receivers, effectively building a mini DMX dimmer system around each receiver, powered by batteries. Dimmer addresses are set with dipswitches on the dimmers themselves.

Integrated systems combine a data receiver with one or more dimmers into a single package. The RC4 Wireless Dimming System takes this approach. There is no access to DMX data from RC4 receivers, but they provide four individually addressable dimmers in a small and lightweight package. Howard Eaton Radio Control is similar, with two- and four-channel receivers available.

In addition to bundled ready-to-go systems, it is also possible to combine hardware from various manufacturers to build a custom system. The state-of-the-art Wireless Solutions W-DMX system can broadcast up to 16 DMX universes (8,192 channels). Receivers can be connected to DMX DC dimmers from RC4 Wireless, as well as any other DMX devices in your rig.

Note, however, that each manufacturer’s radio protocols are proprietary – you cannot use a transmitter from one brand with receivers from another. WDS and W-DMX systems have prioritized the number of channels available, delivering one or more full DMX universes. RC4 and Howard Eaton systems encode fewer channels but provide faster update rates and shorter latency times. The RC4 system is the only system that is truly bidirectional, using the radio link to configure dimmer parameters and monitor battery voltage and temperature, all in real-time from the transmitter front panel.

How Reliable is Wireless Dimming?
Short answer: good wireless dimming is as reliable as wired dimming. (Remember – wire and connectors do fail; DMX termination problems arise; and so on.)

All professional quality wireless dimming systems utilize digital radio and system addresses (ID numbers) to avoid unwanted cross-talk or interference. The transmitter of one system will not operate the receivers of another system unless they are the same brand and set to the same address. They are designed to be tolerant of one another (and other radio devices) operating in close proximity, and users are not required to obtain special licenses from regulatory agencies.

Many of the techniques used to ensure reliability of wireless dimming have been tested and proven in demanding industrial applications. For example, the RC4 Wireless Motion System is based on the same fail-safes and redundancies used for remote-control cranes on construction sites and unmanned locomotives in train yards.

Digital Spread-Spectrum Radio
Traditional radio – as used for wireless microphones, walkie-talkies, broadcast radio and television, most remote-control toys and all but the newest cordless telephones – is “narrowband radio”. In simplest terms, a carrier signal is broadcast on a specific radio frequency. Variations in this carrier represent the information being sent, and cause fluctuations in frequency. Bandwidth is the range from the lowest frequency to the highest frequency used by your application. Narrowband systems are designed to use the least amount of bandwidth possible, with very little overhead. Thus, any amount of interference within that bandwidth can result in noticeable loss of data.

Digital radio is “spread-spectrum” or “ss radio”. First developed decades ago for military applications, ss entered the commercial domain in the late 1980s and became practical and affordable in the 1990s using high-speed and low-cost microelectronic components. Unlike narrowband radio, ss uses a large amount of bandwidth (much more than is required for the data being broadcast) but at very low power levels. It is inherently much more forgiving of multiple users bumping into each other. Interference usually causes little or negligible data loss. In particular, ss radio can effectively ignore narrowband signals, while narrowband radio is oblivious to ss altogether.

The most common forms of ss radios are “direct sequence” or “dsss”, and “frequency hopping” or “fhss”. Both are highly effective. Frequency hoppers tend to be less expensive, and there are various flavors and varieties on the market. Direct sequence radios are more complex and therefore more costly, but are considered more secure against interference and jamming. Nonetheless, either system will work well in most houses of worship, even running along side other ss radio systems. The City Theatrical WDS use fhss; RC4 Wireless uses dsss.

Operating Frequencies
Operating frequency must also be considered. For example, the RC4 system uses dsss in the 900Mhz band, while wifi 802.11 and Zigbee use dsss in the much higher 2.4Ghz band. Thus, they are completely oblivious to one another.

Until recently, there were no frequencies that could be used worldwide for remote control data applications. But, as the upper limit of the useable radio band pushed higher with new technological developments, more and more countries harmonize new allocations. In particular, a section of the 2.4Ghz band is available almost worldwide for unlicensed use with similar limitations on applications and power levels. Predictably, manufacturers are drawn to this band because it allows them to market new products around the globe, potentially recouping investment dollars more quickly. The downside is that many wireless products are being designed to operate in the same band – not just wireless dimming systems, but wi-fi networking, Bluetooth, Zigbee, WirelessUSB, and hundreds (perhaps thousands) of proprietary applications for wireless data across many industries. (To make matters worse, this is also the frequency produced by microwave ovens, which become unintentional radiators of rf interference in a band that is already in high demand.)

Regardless of what your radio application is (narrowband or spread-spectrum, analog or digital), lower frequencies tend to travel further and penetrate obstructions more easily. With the same power output, an 800Mhz signal will provide better coverage than a 2Ghz signal. This is also why 5.8Ghz is not ideal for radio applications requiring significant range, though this very high band has been available for some time.

If your application for wireless dimming does not require international touring, the advantages of not using 2.4Ghz equipment is obvious. As mentioned, the RC4 system uses the 900Mhz band for unlicensed use anywhere in North America. Similarly, Howard Eaton equipment operates in the 800Mhz band for use in the United Kingdom. Both systems can be customized to accommodate the requirements of other specific countries.

When worldwide use is required, the City Theatrical WDS and Wireless Solutions W-DMX both operate in the 2.4Ghz band. The W-DMX uses high output power and optional power boosters to ensure their signal is robust; of course, this could cause problems for other wireless technology in close proximity.

System Addresses, Encryption, and Data Errors
For wireless dimming, a digital system address is much like a password. Every transmitted signal, representing the levels of numerous dimming channels, is encoded with a system address. Receivers ignore data that is not correctly encoded, or contains errors. For example, data packets that are the wrong length, have the wrong address, or do not pass a mathematical validity test will not be used. It is virtually impossible for a properly functioning modern wireless dimmer to turn on when it is not supposed to.

Wireless dimming systems are designed for minimum latency – the time it takes for data to get from transmitter input to receiver output. If a packet is ignored, another will come along before a human observer is aware of a problem. The nature of radio is such that bad packets happen regularly; a well designed system meets performance specifications even with fairly high error rates.

When all is said and done, digital wireless dimming surpasses most expectations – it works magnificently well, even in adverse circumstances.

All Dimmers are Not Created Equal
Nobody likes excessive electrical noise in any setup, and it can play particular havoc with radio signals. Radios like clean quiet airwaves, while dimmers make all kinds of noise. The closer an rf noise source gets to a radio, the more severe the ill effects. It’s a square-law thing: reduce the distance by half and interference will be four times worse. One of the biggest engineering challenges in designing integrated wireless dimming is to package the receiver and dimmer together and still have a functioning radio. Nonetheless, makers of integrated systems have done their homework, and they work very, very well. The RC4 system has even managed to hide the antenna inside the enclosure, avoiding an awkward protrusion.

Physical size and complexity of wiring must be considered if you need to conceal a dimmer in a small space or in a costume. The WDS Personal Dimmer is quite small and provides an integrated dimmer. A competing RC4 model is very slightly larger but provides four dimmers.

The resolution of DMX data is 256 steps per dimmer channel, and most dimmers – wired or wireless – deliver this many levels at the power output. When driving common incandescent and halogen lamps, which look best with a linear power curve, this is fine. It is less satisfactory with LED solid-state lighting, which looks better with an inverse-square-law (ISL) power curve. Problems arise when digital pulse-width-modulation dimmers emulate an ISL curve with only 256 linear steps: the bottom of the curve looks very choppy and quantized. This can be overcome with a native dimmer resolution that is higher than 256 steps, but not all wireless dimmers offer this – most printed specifications simply indicate “DMX resolution”, “256 step”, or “00-FF” (hexadecimal for 0 – 255). Some dimmers, however, do specify native resolutions of 1024, 1328, or even more steps. In particular, the RC4-RX4-HD high-definition dimmer provides 16,384 steps and delivers exceptionally smooth fade-ups.

If you plan to use 12V batteries and lamps most of the time, just about every wireless dimmer on the market will do the job. But pay attention to input voltage range if you plan to use alternative batteries (like 9.6V or 18V power-tool batteries), lamps that operate at voltages other than 12V (like many LEDs), or 24V motors that can draw a lot of power as well as produce back-emf noise that exceeds the supply voltage. Look for dimmers that can drive loads with a different voltage rating than the power supply; you might, for example, want to use 4V LEDs with 14.4V batteries, or operate several different loads from the same battery.

Note the drop-out voltage for receivers and dimmers. The lower this value, the longer your system will continue working as you run down your batteries (though you should avoid running a battery lower than the manufacturer recommends). Drop-out voltage also affects how well the electronics will cope with transients. For example, a large motor might briefly pull a 12V battery down to 9V when it starts up; if the receiver cannot continue operating under these conditions, problems will arise.

Setting parameters for wireless dimmers is handled differently by each manufacturer. Some use dipswitches or rotary controls on the dimmers themselves, while others access parameters via the radio link. The RC4 system, for example, provides a host of features for each dimmer – more than could be easily addressed with hardware switches – that are accessed from the transmitter LCD display and keypad. This makes it easy to change the settings of a receiver/dimmer that is buried inside a prop or set piece; it also simplifies the transfer of settings from one receiver to another.

Take Care of Your Batteries and They Will Take Care of You
By far, the most troubling aspect of wireless dimming is care and maintenance of batteries. If a battery cannot sustain the radio and dimmer electronics while driving the load for the time you need, you will see drop outs, unexpected fades, and generally intermittent behaviour.

To further exacerbate this issue, the capacity ratings on most batteries are misleading. A 10Ah (Amp-hour) sealed lead-acid (SLA) battery will drive a 10A load for only 30 minutes – sometimes less – before it needs to be recharged. This is because batteries are most efficient when driving small loads for extended periods. That same 10Ah battery will drive a 1A load for nearly 10 hours, and a 0.5A load for a full 20 hours without a problem. Most published battery specifications use the 20-hour rate to keep their numbers looking good.

12V lead-acid batteries remain the power of choice for wireless dimming, particularly when the loads are MR16 halogen lamps. Nonetheless, more and more users are turning to NiMH (nickel-metal-hydride) with LED lamps. With higher energy density and fewer “memory effects” than NiCAD (nickel-cadmium), NiMH is ideal for small props and costumes. The reduced power draw of LEDs further reduces size and weight.

No matter what batteries you use, they will wear out. Life expectancy is determined primarily by the number of charge cycles, but allowances should also be made for age, storage conditions, and how deeply the battery is discharged on each use. In theatrical applications where rechargeable batteries are used 7 to 10 times per week with high discharge rates, batteries may require replacement as often as 3 or 4 times a year. In a house of worship using batteries once or twice a week, life expectancy can be considerably longer – up to several years – provided they are stored at room temperature and charged shortly before use with a high-quality “smart” charger.

Making Wireless Work for You
Wireless dimmers provide myriad ways to add impact to sermons and stir your congregation. Effects that would be difficult or impossible with wires become simple with radio and batteries. Systems on the market today are mature and reliable, and all are well supported by the people who make and sell them. There has never been a better time to incorporate wireless dimming – and motion – in the worship setting.

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