Let's ask ChatGPT: "I set up a rotary beacon in an Atlas N scale RS-11 with a Digitrax DN147A0 DCC decoder using an auxiliary function. I don't like how quickly the beacon rotates. Is there is a way to 1) slow down the flash rate on the function and 2) dim the brightness?"
Reply: You are using a Digitrax DN147A0, which supports FX3 lighting effects. Both the rotation speed and apparent brightness of a rotary beacon are controlled primarily by CV62, while the function output must be assigned the correct FX effect.
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1. Slowing down the rotary beacon (flash / rotation rate)
The flash rate for all FX3 lighting effects is controlled by CV62.
CV62 range: 0–255
The behavior breaks down as follows:
* The value from 0 to 15 controls the effect speed
* Lower values = faster flashing
* Higher values = slower flashing
* Values above 15 add baseline brightness (covered in section 2)
Typical speed values:
* CV62 = 0 very fast (default)
* CV62 = 4 slightly slower
* CV62 = 8 moderate
* CV62 = 12 slow
* CV62 = 15 slowest possible
To slow the beacon, increase CV62 toward 12–15.
Example:
CV62 = 10
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2. Dimming the beacon brightness
Digitrax FX3 decoders do not provide true PWM dimming, but you can reduce apparent brightness by controlling the baseline output level using CV62.
Brightness behavior:
* Every increase of 16 adds baseline brightness
* Baseline levels:
* 0–15 LED fully off between flashes (best for realism)
* 16–31 slight glow between flashes
* 32–47 noticeably brighter
* 48+ usually too bright for N scale
For N scale beacons, values below 32 are generally preferred.
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3. Combining speed and brightness
Speed and brightness are combined by adding the two components together.
Examples:
* CV62 = 10 slower rotation, dim between flashes
* CV62 = 26 slower rotation, slight glow
* CV62 = 15 slowest rotation, fully off between flashes
* CV62 = 31 slowest rotation, slight glow
CV62 = 10
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4. Assigning the rotary beacon effect to a function output
The function output must be programmed as a rotary beacon effect.
FX3 function CVs:
* F0 forward CV49
* F0 reverse CV50
* F1 CV51
* F2 CV52
To select a rotary beacon effect, the CV value must end in 6.
Example, beacon on F1:
CV51 = 6
If direction or other qualifiers are used, ensure the last digit remains 6.
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Recommended final setup example
CV51 = 6
CV62 = 10
This produces a slower, more realistic beacon rotation with reduced apparent brightness.
If you want finer tuning, you can also reduce brightness further with a higher-value series resistor on the LED (typically 1.5k to 3.3k ohms for N scale), which gives the most realistic result in combination with CV62 adjustments.
End of ChatGPT answer.
Give this a try. Jot down the current value of CV62 first as a reference. I'm thinking a series resistor will do a better job of reducing the brightness of the LED than tweaking the CV62's upper nibble.
