Adding sound, internal lighting & hazard lights to the Hornby Class 156 two-car DMU.

(This Class 156 unit already has day and night running lights plus a front deflector, fitted)


Click on the  image on the right for a larger picture


Please be aware that this webpage is now over 10years old.

Many of the parts described below are no longer available.

However in most cases better solutions can now be sourced.



This project uses the running lights equipped Northern Rail "Settle-Carlisle" Class 156 as its starting point. A sound decoder and speaker system, internal lights within the passenger compartment and external hazard lights will be added to the cars.


Hornby sales pic. of the original Settle-Carlisle 156 pair

A summary of the planned changes:

The plan is to replace the current power car decoder with a 21 pin Howes LokSound V4 decoder with adapter pcb (providing 6 function outputs). In the trailer car, the existing decoder will be replaced by a 6 function Lockpilot FX decoder. A large base reflex 4 ohm speaker will be fitted in the below-floor-moulding of the trailer car, connected to the front car via a two way miniature connector. (This enables the power car to retain the traction enhancing ballast weight situated in the corresponding position.) 

The internal lighting will use 4 or 6 pure white chip LEDs per car, beaming up towards a white painted roof underside, to spread the light evenly. These LEDs will be powered by an anti-flicker "stay alive" circuit in the trailer car. In the power car, stay alive capacitors will be fitted to the entire decoder.  Surface mount amber LEDs will be fitted in holes drilled through the painted-on hazard light locations half way along the car sides just below roof level. (These lights come on whenever the doors of the car concerned, are open.)

The existing single sided electrical pick ups on the trailer car will be enhanced to provide pick-ups on all 8 wheels.

The lighting control will be via button 0 for day running lights, button 4 for the hazard lights, button 11 for night running lights, button 12 for the internal passenger compartment lighting and button 14 for the power car cab light. The sound functions on the Howes decoder will be re-mapped as necessary to achieve this arrangement.

I've ordered up some "sitting passengers" and if all goes well, I'll populate the passenger compartment with some of these.  I'll also install a scale driver in the power car, if there is room to add a rear cab wall in front of the pivoting motor housing.


The starting point


Circuit Diagrams:

Power Car Circuit


Trailer Car Circuit


"Stay Alive / Flicker Free" Circuit for Trailer car Internal Lighting

The trailer car circuit above has been updated to cover a modified lighting arrangement with the LEDs facing downwards & requiring circa 4.5mA of current


Preferred LokSound Function mapping:


Button Sound Operations Lighting
0 (Forward)     Day running forward
0 (Reverse)     Day running reverse
1 Engine & sounds on/off    
2 2 tone horn    
3 Single horn    
4 doors open   hazard lights on/off
5 guard's whistle    
6 doors close    
7 Right Away buzzers    
8 Flange squeal    
9   shunt mode  
10   Zero CV3 & 4  
11 (Forward)     Night running forward
11 (Reverse)     Night running reverse
12     Interior passenger lighting
13 Inverse 2 tone horn    
14     Cab light
15 Volume fader    



O.K. That's the plan..... Lets make a start:


The Construction of the cars   (trailer car is illustrated below):

First the upper body shell must be separated from the wheeled chassis unit.  The lower edges of the sides are carefully prized away from the chassis unit to release the 8 plastic clips holding the two parts together. This is not an easy operation!  The roof can then be removed from the upper body shell by releasing the eight clips holding these two parts together. (See picture below for the location of the clips.)


Fitting a driver in the power car cab:

There is just room in front of the pivoting motor bogie, to insert a rear cab wall (1mm plasti-card).  The front lighting series resistors don't leave a lot of space for much more than a Northern Rail driver and his seat back. An additional LED will be fitted above the driver, activated by the LokSound decoder output, Aux4, via button 14.

Driver glued in place (looking up into the upper body shell from underneath)

Hope he knows the way to Huddersfield! (  >>>  )



A convenient location is identified for the large "Stay Alive" capacitors:

There is room to fit three 1000uF 25V electrolytic capacitors, beside the ballast weight in the power car chassis assembly. The weight had to be shifted a few mm towards the rear in order to make enough space to fit two of the capacitors side by side. The capacitor leads are connected in parallel and connect to the upper body, using spare ways in the 8 pin NMRA plug and socket. The capacitors are held in place by pieces of Blu Tack.

The underside detail maybe a bit lacking, but at least there's room for the capacitors


The 3 capacitors are wired in parallel and connected to two spare sockets on the 8 way NMRA connector.


Hazard lights:

A rectangular hole is cut through the plastic body shell in the centre of the orange square. (Using first a drill, then a needle file). The amber LED leads are run through the hole and a very small blob of Blu Tack is used to hold the rear of the LED in the correct position, while clear adhesive is applied over the outside surface of the LED and the edges of the aperture. When the clear adhesive is completely dry, orange water colour paint is applied over the lens of the new hazard lights.

Original Printed on Hazard light

LED glued in place (On the other side of the car)


Power Car LokSound Programming to remap the buttons

First the sound slot numbers are found by interrogating the 3 CVs assigned to each sound trigger button (click here to see the chart I use for this job). The sound slot numbers appear in column 3 below.  

Button LokSound as received with Howes mapping Sound slot as received Required Sound Req'd Logic Required Lights Mapping Changes Needed (SS= Sound Slot)
0 Forward Lights Forward -     Day running forward None
0 Reverse Lights Reverse -     Day running reverse None
1 Engine start 1 Engine & sounds on/off     None
2 2 Tone Horn 3 2 tone horn     None
3 Inverse 2 Tone Horn 10 Single horn     Delete SS 10;  Add SS 4
4 Single Horn 4 doors open   hazard lights on/off Delete SS 4;    Add SS 5 and  Hazard lights on Aux3
5 Doors Close 7 guard's whistle     Delete SS 7;    Add SS 11
6 Doors Open 5 doors close     Delete SS 5;  Add SS 7
7 Right Away Buzzer 8 Right Away buzzers     None
8 Flange Squeal 9 Flange squeal     None
9 Shunt Mode -   shunt mode   None
10 CV3 & 4 Set To Zero -   Zero CV3 & 4   None
11 Forward Aux 1 -     Night running forward Make forward only
11 Reverse Aux 1 -     Night running reverse Assign new mapping line as F11 reverse only, for Rearlight
12 Aux 2 -     Interior passenger lighting None
13 Guards Whistle 11 Inverse 2 tone horn     Delete SS 11;   Add SS 10
14   -     Cab light Set to Aux 4
15   - Volume fader     Assign to Volume Fader & set CV133 as required

CV Changes Required:

Button Mapping Line CV Changes                     (2/399    2>0   means: With CV32 set to 2, change CV399 from 2 to 0).....etc
3 9 2/399 2>0 ;  2/398 0>8
4 10 2/414 8>16; 2/410 0>16
5 11 2/430 64>0; 2/431 0>4
6 12 2/446 16>64
11 Forward 17 3/257 0>4
11 Reverse 40 4/369 0>8; 4/372 0>4; 4/378 0>2
13 19 3/303 4>2
14 20 3/314 0>32
15 21 3/333 0>8;               133 128>75                                 63  128>40




Adding A Few Passengers:

The central glazed roof sections have been partially removed to improve access and (hopefully) to improve the internal lighting. The figures are from the Noch HO range. Hopefully the unusual clothing contrasts will not be so obvious when viewed through the finished train windows.


Fitting the Interior Lights:

White LEDs on cross-beams facing up towards the white painted roof, plus another pair facing downwards below the decoder

(The decoder & adapter PCB are not connected & have just been put in place to test the lighting)


The lighting effect when the roof is temporarily placed over the car


Although the use of LED light bounced off the white painted coach ceiling, gives a well distributed even lighting effect, the two LEDs pointing downwards from under the decoder PCB, create a brighter effect (Or draw much less current in generating a similar light level.)


Adding the Cab light LED:

The cab light is simply a chip LED hanging on its leads in the top of the cab. The chip has been deliberately tilted down at the front to minimise light escaping directly through the windscreen.

ESU Adapter board wired in


Fitting the Decoder adapter board:

ESU supply an adapter PCB that provides wired access to the 21 pin decoder connections. The adapter board also includes amplifiers for the two additional LokSound function outputs, with minimal current switching capability. Also, easy access to the ground connection is provided (required for stay-alive capacitor connection).  On the 156, the adapter board is mounted so that its top surface is level with the top of the internal glazing moulding. This leaves just enough room below the roof for the decoder to fit. The additional ground, V+, Aux3 and Aux4 wiring was first added, then with the adapter board lightly glued in place, all the wiring was trimmed, routed and soldered in place. (held down with clear adhesive). The track connections, motor wires and stay-alive capacitor wires were connected to the 8 pin NMRA plug, ready to provide the interconnect between the upper body assembly and the chassis.

ESU Adapter board wired in


Adding the Power Car speaker socket:

The speaker is mounted in the trailer car so that the ballast weight in the lower body housing of the power car can be retained.  A miniature TCS twin socket is super glued to the end of the car, with the leads passing through two small holes drilled in the end wall.

The speaker socket glued in place before it's connected up.


Fitting the decoder and completing the wiring:

The decoder in place, plugged into the adapter board. The speaker wires are taken directly from the decoder for higher reliability and slightly less resistance.


The wiring is fitted above the glazing moulding, with care taken to leave the roof clip apertures clear of obstructions.


Oops!  It works much better when an 8 pin plug is used instead of a DCC ready DC-blanking-plug with shorting links built in!


Optimising the motor control CVs:

156 on the test track with temporary piggyback speaker connected to the rear socket.

Initial results with defaults were disastrous, so I immediately ran the auto-optimisation routine by setting CV54 to zero and running the loco down a straight test track by pressing F1. However, although the resultant performance was better than with the defaults, movement using the lowest two speed steps was still very jerky. By experimental optimisation of the CVs, one at a time, I achieved smooth running on all except the first speed step. Reading the details in the manual gave a few more clues and I eventually homed in on a smooth solution even for speed step 1. However, a slight and variable tendency for jitter still occurs when moving between speed steps one and two (in either direction). This maybe due to mechanical issues, but the effect is fortunately not too obvious, particularly under computer control.

CV First Auto- optimised result Manual optimisation 1CV at a time Best solution so far
51 0 0 3
52 12 14 30
53 69 140 140
54 21 90 50
55 12 12 12


Next, the trailer car.......

Fitting the speaker and a new ballast weight to the chassis:

The original trailer car ballast weight (52gm) obstructs the speaker location. This was therefore removed and holes were cut in the chassis underside to correspond with the cone and base port of the new speaker.  A new ballast weight was trimmed to fit beside the speaker (58gm this time). The speaker was super-glued to the chassis base and the new ballast weight was held in place using double sided foam tape.

Chassis top view showing the speaker & ballast weight


Underside view showing the speaker apertures


Adding wheel contacts to the unmodified half of each bogie:

Additional wheel wiping contacts were added to each bogie, using 1mm wide phosphor bronze strip. The wipers are pre-formed and then fixed in place using superglue at the mounting point near the centre of the strip, where a plasti-card block clamps the strip to the bogie centre plate. A wire will be soldered to the strip when the glue has dried.

Additional wheel-wiper strip added (towards the top of the photo)..... Those wheels need a clean!



Trailer Car Decoder and Stay-alive capacitor locations


The area in the trailer car corresponding to the motor location in the power car has blanked off windows, making it an ideal electronics bay. The decoder is mounted using double sided tape on the side of the car.

Near the cab end of the trailer car, showing the decoder.

Capacitor Location:

Opposite the decoder is space for two 1000uF 25Vcapacitors


Adding a few passengers:

More of the Noch seated passengers were glued to appropriate seats.


Passengers added. (The wiring visible in the above photos is associated with the hazard lights).


Trying direct illumination in the trailer car instead of bouncing the LED light off the ceiling:

The lower current required by the two front cabin LEDs below the decoder in the power car, would suggest that as long there are enough LEDs to give a reasonably even light level, then fitting LEDs in the roof, beaming downwards should give a significant improvement in lighting efficiency.

Doing some simple sums, alternative emitter resistor values for the constant current sources in the anti-flicker circuit should result in the reduced LED current values indicated in the table below. I will have to experiment to get the overall light level similar to that of the power car.  Have to pop over to Maplin tomorrow to get some more low value resistors!

Emitter Resistor Value (Re) Corresponding LED current
56 ohms 8mA
100 ohms 4.5mA
150 ohms 3mA
220 ohms 2mA

Showing the resistors that determine the LED brightness in red (Re)

Running the downward facing LED solution using temporary series resistors, a current of 4.5mA through each LED gave a similar light level to the upward LEDs in the power car, so if I build with 100 ohm emitter resistors, results should be about right.

Re = 100 ohms

Interior lights and flicker-free circuit added


The underside of the lighting assembly, showing the downward facing LEDs


Close-up of the anti-flicker circuit, located in the top of the electronics bay.


Speaker 2 pin plug and cable


Programming the Trailer Car LokPilot FX decoder:

The CVs need to be adjusted to switch the appropriate lights using the same lighting buttons as the power car:

Description CV numbers Value
Button 0 forward  (Rear lights, yellow) 141 2
Button 0 reverse (Day headlight, white) 144 1
Remove Button 1 defaults 147 & 150 0
Remove Button 2 defaults 153 & 156 0
Button 4 forward (Hazard lights, orange Aux3) 165 16
Button 4 reverse  (Hazard lights, orange Aux3) 168 16
Button 11 forward (Rear light, yellow) 207 2
Button 11 reverse (Night headlight, green Aux1) 210 4
Button 12 forward (Internal lights, purple Aux2) 213 8
Button 12 reverse (Internal lights, purple Aux2) 216 8

All lights now working as planned!


Final optimisation:

The relative sound levels need some adjustment...... e.g. a drop in engine sound level compared to the horn sound level.

Sound Sound Slot number Volume CV Initial Value Final Value
Register setting - 32 1 1
Engine 1 259 128 90
2 Tone Horn 3 275 128 128
Single Tone Horn 4 283 128 128
Doors open 5 291 128 128
Guard's whistle 11 339 128 128
Doors close 7 307 128 128
Right away buzzer 8 315 128 128
Flange squeal 9 323 128 128
Master Volume - 63 40 40
fader volume - 133 75 75


Also, the rear lights are a bit too bright and these need toning down a little. Easier at this stage to use the decoder software than to change the series resistors!

Description CV numbers Value
Power Car Register 32 0
Power Car Rear lights intensity  (range: 0-31) 270 from 31 to 15
Trailer Car Rear Lights intensity (range: 0-15) 114 from 15 to 4


The speaker cables can be seen where they emerge into the passenger compartment. Soon resolved with the use of appropriate paint.


Finally some night running images on the test track, prior to computer schedule optimisation


Power Car


Front view


Rear Car (with speaker cable just visible)


To watch a YouTube video demonstrating the sound on the test track, please click here


Supplier website links:


Hattons of Liverpool    The Class 156 unit above was purchased (quite some time ago) from this very reliable mail order company.
South West Digital    Official ESU supplier. The Lokpilot FX function only decoder and ESU adapter board were sourced here.
Digitrains    Excellent source of specialist DCC devices for this type of project. (the Nano-LEDs came from here).
DCC Supplies    DCC specialist supplier based in Worcestershire. The base reflex speaker and miniature connector came from here.
Howes Model Shop    The LokSound V4 decoder (as also used on the similarly engined Class 150/2) was sourced from here (with additional guard's whistle thanks to Bryan).
Maplin    Convenient local source of electronic components, such as the 1000uF 25V "Stay Alive" capacitors


The photos of real class 156s were taken at Carlisle during June 2009.   The photos of the model were taken hand held on the kitchen worktop using a Canon Ixus 220HS.    


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