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RC4 Knowledge Base

Changing PWM Frequencies for Video Applications (LumenDimM4)

I. Changing the PWM frequencyPWM frequencyPWM stands for Pulse-Width Modulation.  It is a method for using a switching device (one that can only be on or off) to create what appears to be analog changes in level.  This is done by switching on and off at a high speed and varying the proportion of the time for each.  For example, of the […]
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on the LumenDimM4

A. The unit must be receiving streaming data from the transmitter in this process

1. The yellow LED on the LumenDimM4 will be illuminated when it is receiving streamingStreamingStreaming is the continuous flow of digital control data.  Transmitters stream data out, while receivers receive streamed data.  RC4 transmitters process an incoming stream of DMX data and convert it to a proprietary wireless data stream that is secured with a digital system ID and error checking methods.
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 data

2. Without streaming data, the unit is in bump button mode and will not be able to set functions

B. Multiple PWM frequencies work only for the ISL curves which are used for LEDs

1. PWM frequencies are only significant when working with LEDs

2. When doing video, if bandingBandingBanding is one of several different kinds of unwanted artifacts seen on film or video.
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and beating is present in your shots, the PWM frequency needs to be increased

II. Changing the PWM frequencies on a LumenDimM4 that is restored to default mode (DMX channels 1 to 4) with an ISL slow curveISL slow curveLEDs do not dim linearly: when dimmed to a linear 50%, they appear only slightly less bright than at 100%.  The level must drop to 25% to appear at half brightness.  To make LEDs appear linear, they must be controlled with the Inverse Square Law curve.  All good quality LED dimmers use this technique.  RC4 […]
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dimmer curve

A. To see the blink pattern on the LumenDImM4 clearly, it is recommended that the DMX channel remains down during this process.

1. This is because the dimmers are used as indicators

B. The default frequency of the LumenDimM4 is 5kHz

C. Using a small tool like a bent paper clip, press and hold the Set B ButtonSet B ButtonAll RC4 dimmers have Set buttons for each individual dimmer output. The second button is the Set B button. On a 2-channel device these are Set A and Set B buttons. A 4-channel device adds Set C and Set D. The most common use of the Set button is to assign a DMX channel and […]
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for three seconds to move up to the next incremental frequency

D. The Set A  buttonSet A ButtonAll RC4 dimmers have Set buttons for each individual dimmer output. The first button is the Set A button. On a 2-channel device these are Set A and Set B buttons. A 4-channel device adds Set C and Set D. The most common use of the Set button is to assign a DMX channel and […]
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and Set B button will blink a pattern

1. This  blink patternBlink patternRC4 Wireless devices use small colored LEDs to indicate various modes of operation.  In addition to indicators simply being on or off, they can blink at different speeds or blink with patterns that indicate a particular setting or parameter value.  For example, an indicator might indicate 1 short blink, or 2 short blinks followed by […]
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indicates the newly selected PWM frequency

2. Written documentation provides a blink pattern frequency chart for reference

E. The frequency has now changed to 10kHz

F. The PWM frequency can be made faster using the same process

G. The PWM frequency essentially doubles each time it is adjusted up

H. Currently, the highest PWM frequency offered on the LumenDimM4 is 40kHz

I. Adjusting the PWM frequency once again after it is set at 40kHz will take it down to the lowest frequency, 615 Hz

J. The PWM frequency is remembered

1. When the unit is turned off and then powered back on, the new PWM frequency will remain

2. When restoring defaults, the PWM frequency will return to the original setting of almost 5kHz

Why bother with PWM frequencies — why not just set it to 40kHz?  There are two reasons:

A. Lower frequencies deliver higher resolution, which improves the smoothness of dimming at the bottom end of the curve (very low dim levels)

B. Lower frequencies are more electrically efficient and can deliver more current with less heat than higher frequencies

C. The lowest ISL frequency of 615Hz looks best to the human eye in live entertainment applications

C. Higher frequencies eliminate artifacts in motion-picture capture.  Use the lowest frequency that does the job, usually 5kHz.  Do test shots whenever possible to find the ideal frequency.  LumenDim devices default to 5kHz, optimal for most motion-picture applications

D. The faster the video frame rate, the higher the PWM frequency needs to be.  For very-slow-motion capture (very high frame rate) 40kHz may be required.  Remember that this reduces dimmer resolution and may look a little bit more “steppy” when dimming at low levels, and the dimmer will generate more heat when driving large loadLoadOverall, load refers to something in an electrical circuit that will draw or consume power. It is also typically the largest power draw in an electrical circuit.
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s.

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