Coordinating the hardware & software in my three Zimo equipped Class 66 locos



Paul Chetter has just released a Class 66 Zimo sound project incorporating his new drive system, which he calls "Protodrive".  I was first introduced to Paul's new drive system in the recent Rail Exclusive Northern Belle Class 47 Zimo decoders. I was sufficiently impressed with the behaviour of these locos, to want to fully equip my fleet of 3 Zimo fitted Class 66 locos with Paul's new sound project, as soon as the Class 66 variant was ready.......

It now makes sense to take a close look at the decoder function mapping and the locomotive hardware build standard, to get the three locos operating as far as possible in the same way. This means that Traincontroller PC schedules written for one loco can be used to control trains incorporating any of the three locomotives. This is the first step in a more general review of the entire locomotive fleet, aimed at achieving as much commonality as is realistic. 

The Locomotives:

 GBRF Class 66


Colas Class 66


DB Schenker Class 66


Hardware Differences To be resolved:

1) Speaker:  The DBS and Colas 66s have the big fuel tank, which now incorporates a sealed 20x40mm ESU 50334 speaker in both locos. The GBRF unit is the newer more efficient 66/9 with the small fuel tank. In this loco, the same speaker type is sealed below the fan grill in the roof underside. 

I have had occasional rattles from the fan grill on this loco, so I'm going to bite the bullet and shift the GBRF speaker into the tank as well. The volume of the small fuel tank looks similar to that of the standard 50334 speaker enclosure, so it should still sound OK.  This will also free up space to add some stay alive capacitors in place of the roof mounted speaker (as already fitted to the other two locos).

2) Detonator flash LED: DBS & Colas units now have these fitted and connected to FO6. I have to remove the bogies on the GBRF unit to get to the tank for speaker work, so I'll add a LED here too.

3) Magnetic detector: The GBRF unit has a Hall effect detector mounted on the front bogie.......the others do not. However this has not actually been useful, so the device will be removed, although its wiring will be reusable for the detonator flash LED.

4) Double strobe yard lighting option. The DBS unit has a lighting option allowing all or part of the forward lighting to be flashed with a double strobe effect. This is completely non-prototypical, but it looks spectacular, so I think I'll add this functionality to the other two units.


GBRF loco: Move speaker to fuel tank, fit stay alive caps, remove magnetic detector, add detonator flash LED, add double strobe hardware.

Colas loco: Add double strobe hardware.


GBRF tank speaker takes shape.

Including the motor recess in the backplate.

(To be sealed and painted when the glue has dried.)


Original Circuit diagram. The MX644 has a 2 pin SUSI output, which can be converted to FO7 & FO8 function outputs by adding 128 to the value of C124.

However, on this decoder, FO7 & FO8 are low current logic outputs. Ground volts in the off condition and (ground +5)Volts in the on condition.

A pair of 2N7002 N-Channel MOSFETs convert the outputs to normal FOs. Source to decoder ground, gates to the decoder FOs & output from the drains.

(See below for the final definitive circuit diagram.)

Common function Mapping:

This arrangement is now operating successfully in all three Class 66 locos.

Key Number Function
F0 Directional lights enable (Swiss group 10).
F1 Engine start / engine sounds on.
F2 Brake (to bring loco to a stop).
F3 Hi horn tone (playable).
F4 Lo horn tone.
F5 Mode switch.
F6 Revert engine to idle.
F7 Ramp up engine.
F8 Reserved.
F9 Reserved.
F10 Reserved.
F11 Flange squeal.
F12 Spirax valves.
F13 Driver's door open / close.
F14 Pre engine start sounds / post engine start sounds.
F15 Buffering / coupling.
F16 Triple detonators.
F17 Detonator flash LED. (Swiss group 9).
F18 Brake air release.
F19 Cab light (Swiss group 2).
F20 End 1 day running lights (Swiss group 3).
F21 End 2 day running lights (Swiss group 4).
F22 End 1 night running lights (Swiss group 5).
F23 End 2 night running lights (Swiss group 6).
F24 End 1 double strobe effects (Swiss group 7).
F25 End 2 double strobe effects (Swiss group 8).
F26 Parking lights (rears both end). (Swiss group 1)
F27 Volume down
F28 Volume up


Thanks to some discussion with Paul, I'm using the Swiss mapping arrangements exclusively for lighting control now, using it in a way that enables keys to be selected "additively" to create the desired effect.

For example, to set directional daytime light engine running lights at both ends, F26, F20 and F21 are on together, with all other lighting keys off.

DBS & Colas 66s running with the revised function mapping above.


GBRF 66 update nearing completion.....just the MOSFET buffers and remaining 21 pin connections to finish.


Mark 2 Circuit:

The original circuit could not operate the strobe headlights without flashing the marker lights as well, which looked an unlikely combination. However, I can't just drive the markers independently as even with a Zimo decoder, I've now run out of function outputs...... so a bit of lateral thinking was required to get an independent supply to the markers:

The two PNP transistors act as direction specific positive supply switches for the headlights and markers, enabling the negative ends of the markers to be

connected together and controlled by a single FO. The same technique is applied to the day headlights and also  to the night headlights.

 This frees up an additional FO, enabling me to keep the markers on while strobing the headlights (and saving a lot of diodes compared to the first circuit!)


The DBS Class 66/0 has the older separate lower marker lights, which on the model are connected in series with a common 47k resistor, while the newer GBRF and Colas units

 use New Tech LED  combined marker/rear lights, which on the models are connected in parallel with individual series resistors. So both options are illustrated above.


Many of the FOs have also been re-assigned, requiring a lot of Swiss mapping adjustments to achieve the options I need:

The Swiss mapped function outputs are now arranged as shown below, using all 10 available groups.




 Use of M-key

Fwd 1

Fwd 2

Rev 1


Parking (rears at both ends)








Directivity Enable F0








End 1 (day) (+F1)








End 2 (day) (+F1)








End 1 (night)  (+F1)








End 2 (night) (+F1)








Strobe End 1 (+F1)








Strobe End 2 (+F1)








Cab light








Detonator flash



F16 M-key





Parking lights can be used with just FO26 active, but the remaining running light options require F0 active, to enable the direction sensitive positive feeds.

The lighting keys can be used in combination to achieve double ended light engine configurations (day running = F0 + F20 + F21 while night running = F0 + F22 + F23).

When a train is hooked up to either end of the loco, the running lights at the train end can be shut down independently by removing that key from the combination.



To see a Youtube video of the locomotives in action, please click this line




Supplier website links:

Not too many entries to include, because of the nature of this webpage. Paul's contact info is of course provided with his agreement. Email address to contact Paul Chetter if interested in obtaining Zimo decoder re-blows to incorporate his sound projects.

Paul also produces occasional newsletter emails, with information concerning new Zimo sound project issues, contact him if you would like these sent to you.

Digitrains Good source for all things DCC including prewired Nanolight chip LEDs, ESU speakers and a range of Zimo and ESU sound project equipped decoders.





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