Firebox flicker light for Flying Scotsman

[vito_bellissimo]

Hi all, I wish to achieve a flickering firebox effect on my Hornby Flying Scotsman. I only have a Hornby Select and I do understand that I cannot change CV values on it. Could I change the CV values at a local hobby store? Additionally, which decoder should I use (Sapphire, Lenz, Hattons). I preferably want to purchase one of the Hattons decoders as they are easy on the wallet. What do you guys think?  

[96RAF]

Firstly you need either a decoder that can provide SFX on the (lighting) functions to get the flicker or you need a flicker module which will work on most decoders. Sapphire can definitely do this - see the downloadable leaflet for it - as can many other decoders - check their specifications.

 

Your Select whilst not being able to change CVs will still be able to operation the associated function. As you say you could get a model shop or a friend to make the CV changes for you.

 

Your other problem will be space for the decoder, especially if using a large decoder like Sapphire and actual firebox light as it may be a single or double led (red and/or yellow) or a bespoke flicker module.

Rob

[vito_bellissimo]

A Sapphire decoder seems like a sensible choice, as a Hornby decoder with a Hornby Select will obviously work. But I might try out a Hattons decoder first and see if there are any issues with it working with my Select, obviously as this is a Hornby forum, I am not promoting the product. If it does not work, i'll definitely invest more into buying the quality Hornby Sapphire. I would assume that the Sapphire decoder would fit into the Scotsman as it is DCC Ready, I would check out the dimensions of it first if I ever get to the stage of purchasing one. 

[vito_bellissimo]

Another thing I will point out is that I will only be using a single red LED as the flicker modules would most likely cost three times as much as a single LED. 

[pidder]

Flickering LEDs are easily available, random flicker, just need wiring via a suitable resistor, to the take off from the pick-ups, on all the time, of course....simples... 

[Chrissaf]

If you adopt Pidder's suggestion (certainly worthwhile considering as a very low cost option), do include a standard diode (something like a 1N4002) in parallel across the LED (physically the opposite way round) to protect the LED against high reverse bias voltages (see note below in italics). This will improve the life of the LED as it will stress it less, electrically. The current limiting resistor needs to be a minimum 1,000 ohms, personally I would increase the resistor to either 1,800 or 2,200 ohms (these are standard resistor value options).

.

Why do this theory: DCC Track voltage is typically 28 volts peak to peak. Without the additional protection diode, the LED will be getting the full 28 volts reverse bias voltage across it, but only 0.6 volts with the protection diode in circuit. LEDs are more sensitive to reverse bias voltage damage than standard diodes.

 

[pidder]

Chrissaf  can I ask why the diode in parallel, rather than in series?...

[Chrissaf]

@Pidder,

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Series will work too.......

.

But putting it in parallel evens out the current draw. Looking at the current with an Oscilloscope, the 'in series' circuit would have alternating pulses of current / no current. The 'in parallel' circuit would have a more consistent current flow through the circuit and a more balanced impedance presented to the DCC data signal. This would minimise the risk (albeit slight) to affect the ability of the loco decoder to read the DCC data signal.

.

(For other's. If used in series, then the protection diode is physically wired the same way round as the LED).

[pidder]

Chris thanks, 

[Rog RJ]

Why not connect the flickering LED to one of the decoder function outputs?  It would then be controllable and no need for protection diodes.  Still need to include the current limiting resistor though.  Much better IMHO than connecting directly to the pickups.

 

[vito_bellissimo]

Can I suggest, maybe if I have it in series, I could benefit from the inconsistent current flow as that itself would create a flickering light! I'm probably wrong here but would that actually achieve the effect? 

[vito_bellissimo]

I might try and find one of those artificial candles lying around at home and take the LED out of it. I agree with Rog here, I could just connect it to the green or purple wire and then to the common postive (Blue) wire on any ordinary decoder. There wouldn't be any need to change the CVs anyway because it is already a flickering light. 

[96RAF]

@Vito

Couple of things wrong with your assumptions - the phased DCC voltage is too quick to allow a flickering effect - due to the persistance of our vision - others have tried the flickering candles and they don't seem to work correctly on decoder function voltages. I have no idea why, but probably down to voltage and mA current flow as output from the decoder.

Rob 

[Chrissaf]

Can I suggest, maybe if I have it in series, I could benefit from the inconsistent current flow as that itself would create a flickering light! I'm probably wrong here but would that actually achieve the effect? 

.

No, because the the DCC signal operates typically at between 7,000 and 12,000 cycles per second. Too fast for the human eye to detect any flickering.

.

Edit: Opps hadn't noticed that Rob had already given a similar answer.