Hogwarts Castle Headlamp Control

[JK1707821688]

I recently purchased the Hornby R3216TTS “Hogwarts Castle” locomotive. It is a rather nice model and I do like the very bright LED Headlamp feature. However, what I do not like is, the moment this Locomotive is on the DCC track, the Headlamp is permanently on. There is no Decoder option that allows you to turn the LED On or Off which is somewhat annoying to me.

Due to this, I decided to use one of my surplus Hornby R8249 Decoders, to rectify this situation. My intention was to use the Front Directional Lighting wires of the Decoder to give me the desired control. The White wire is the for the Front Light and the Blue wire is the Common. The Red & Black wires are the Power leads.

The first thing that needs to be done is to program the R8249 Decoder, with the same Digital ID as that of the Locomotive, in my case 5972. I then cut the 8 Pin plug off so that less space would be occupied when the decoder has been installed. Whilst in Railmaster and being an optimist, I set the Hogwarts Castle Function F0 to Headlamp On/Off and saved. At this time, to make life a little easier, I disconnected and removed the Tender.

I then carefully separated the locomotive Body from its Chassis. There is an LED regulator PCB screwed to the chassis to which the LED Headlamp is soldered. This LED regulator PCB needs to be removed from the chassis (a single screw) to allow the Red & Black power leads from the Rail Pickups to be unsoldered. It is a good idea to take a picture of these wires before unsoldering so you connect the R8249 the correct way around. If there is any confusion later on, each power input is marked with the letters LT (-ve) & RT (+ve) on the underside of the LED regulator PCB.

The R8249 White & Blue wires are then soldered to the LED regulator PCB (White +ve & Blue -ve). Then it’s a matter of soldering the R8249 Red & Black wires to the Red & Black Rail Pickups previously unsoldered from the LED regulator PCB. That’s all the soldering done. At this time, it’s advisable to check that the lighting control is working correctly, before re-combining the Chassis and Body.

The LED regulator PCB then needs to be re-attached (single screw) to the Chassis prior to closing up. There is plenty of room inside the boiler to accommodate the R8249 Decoder but care needs to be taken when closing the Body & Chassis. As there is hardly any gap between the Chassis sides and the Body it is quite easy to snag/pinch any loose wires. The Tender is re-attached and re-connected to the Locomotive.

You should now be able to Turn the Hogwarts Castle LED Headlamp On/Off at will using Function F0 (in Railmaster). It will also be seen that when the Locomotive direction of travel is in reverse the LED Headlamp, as expected, turns off. However, it does not turn off immediately, but fades to off taking about 3 or so seconds. I believe this is due to a small electrolytic capacitor which is on the LED regulator PCB. If anyone is wondering, the LED Headlamp will not work with the R8249 Decoder, without the LED regulator PCB being part of the circuit (See my latest Post below as this statement may not be correct).

I hope this submission is of some value to others who feel the same way about the lack of Headlamp Control with the Hogwarts Castle Locomotive.

[96RAF]

Are you saying you have installed the R8249 in addition to the TTS decoder purely to operate the headlight. If so you could have performed the same mod using the TTS green wire and switched using F25 (aux function).

Blue wire is positive output from a decoder and the function output wires white, yellow and green are floating negatives until selected, so I am surprised you connection the the led regulator worked as written.

[Chrissaf]

Presumably the white wire on the original TTS decoder was not being used either as well as the green. Therefore the TTS white wire could have saved installing a second decoder.

The onboard, LED regulator I would expect to be designed for a track voltage input, 3 to 12 volts input on DC and DCC voltage after rectification of about 13 volts. Thus the 12 volt output of the decoder function would be compatible with the regulator input.

The rhetorical question I would be asking, is why didn't Hornby make the front headlight DCC controlable in the first place. If I had to quess at an answer, it would be because the front Hogwarts Express headlight was never meant to be directional. So yes they could have linked it to the green decoder function, but that would over complicate things when trying to make the lamp also function on DC as a DCC Ready loco. Although I see no reason why an electrical slide switch could not have been incorporated in the chassis base to switch between DC and DCC.

[JK1707821688]

To answer 96RAF 1^st, Yes, the installed R8249 Decoder is additional to the Tender fitter TTS Decoder. I was aware that the required Directional lighting could be derived from the Tender TTS decoder but meant extra wires between the Tender and Locomotive which I did not want to do.

Re the Blue wire, on all documentation that I have seen, the Blue wire is the Common with the White, Yellow & Green wires being the Lighting feeds F0 / F25. My knowledge of standard electronics notation has always been accepted by me as Common representing Common Earth.

Obviuosly, in this case, my decoder polarity understanding is incorrect although the arrangement I have described works absolutely fine.

As stated in a previous Post, I have upgraded a number of my locomotives with TTS Decoders meaning I have a number of R8249 Decoders surplus to requirements. Rather than throw them in a box and forget about them, I have looked for ways to utilise these decoders. Hence the over-the-top use of a R8249 Decoder, to control the LED Headlamp on the Hogwarts Castle Locomotive, representing 1 less £18 DCC Decoder going to waste.

I do agree with the comments made by Chrissaf that some form of Control could-should have been included. A slide switch is a very simple & practical solution but just doesn’t seem to be in keeping with DCC philosophies or functionality. I wanted to control the Headlamp from the comfort of my laptop – Railmaster rather than a manual switch.

Anyway, I am more than happy with the end result which fulfilled my Original Intention.

I did appreciate the prompt Feedback from the two of you (96RAF & Chrissaf).

[Chrissaf]

Re the Blue wire, on all documentation that I have seen, the Blue wire is the Common with the White, Yellow & Green wires being the Lighting feeds F0 / F25. My knowledge of standard electronics notation has always been accepted by me as Common representing Common Earth.

Whether I’m correct or not, the arrangement I have described works absolutely fine irrespective of our different viewpoint on which is -ve or +ve.

 

 

In many electronic scenarios it can be the convention that a common is negative. DCC decoders buck this trend and the common is positive, this is further compounded by the specifications stanardising on the decoder common positive being assigned a blue colour. Blue of course is typically considered to be a negative voltage colour as well as black.

The reason that this made no difference to powering your headlight is because the LED regulator circuit would be fronted by a bridge rectifier to make it compatible with DCC which is an alternating track voltage. Thus the bridge rectifier will accept the blue / white voltage input either way round.

You make a valid point about decoder location being in the tender needing additional wiring between loco and tender if lamp was controlled from the TTS decoder.

With regard my slide switch comment, in DC position I envisaged that the lamp would be powered as per factory solution, but in DCC position the input to the lamp would be diverted to the output of the decoder to give DCC control, but that would need either the decoder location design to be revised or the 4 wire link wire upgraded to 6 wires. Which upon reflection and taking the decoder location into account, is probably the reason why Hornby designed the lamp circuit the way they did. The switch position would be set at the time of purchase subject to layout being DC or DCC powered and then left in that position.

[JK1707821688]

Hi Chrissaf,

Many thanks for your really great explaination about the Blue wire polarity issue. When the issue was raised by 96RAF, I guessed there may have been some form of rectification on the LED regulator PCB, making the Decoder polarity issue somewhat moot. I am now wondering if the LED regulator PCB is required at all, as I would have connected the LED to the Blue/White wires the wrong way round, hence the LED didn't work. That said, as all works as I wanted, I shall leave things as they are. Again, Thanks for the excellent clarification.

[Fishmanoz]

If you were to remove the board, you would also need to add a series current limiting resistor as well as getting the polarity correct. The board may already include such a resistor as a brightness limiter, the current not being a problem when connected to the track as designed.

Chris, from the 2nd Hogwarts DCC Ready loco on, the same light arrangement has been used. The first didn’t have a light. I cannot see them finding it value to change the design now with a switch when they didn’t do so with the decoder socket previously in the loco in earlier models.

[Chrissaf]

The switch comment, was meant more of a should or could they have done this at the design stage rather than suggest they change the tooling.

The statement above makes more sense if my first reply mentioning a switch is read rather than the follow up second reply switch comment.

[JK1707821688]

Since receiving Feedback from 96RAF, Chrissaf & Fishmanoz, I have never been totally happy with my Hogwarts Express Healamp Fix. So today I decided to remove the LED Converter Board and connect the R8249 Decoder Chip directly, as suggested, to the Headlamp LED with a 1Kohm Resistor. The Headlamp works perfectly, as it should, with no On/Off delays. As my Locomotive was already dis-assembled, I thought it would be a good time to fit a Red LED on the right side above the front Buffer Bar. This Reverse Direction LED is connected to the Common Blue Wire (+ve) after the Resistor and the Yellow Wire so that Locomotive now has DirectionaI lighting to the Front. Obviously, both the Headlamp & Reverse Lamp can be turned On/Off via F0 in Railmaster. I am now Happy with this much neater/efficent fix.