DCC 21 Pin MTC connection decoders

[Yorkshire Dave]

This is really to act as a guide if you wish to use your favourite 21 pin decoder in some of the later RTR releases. The Dapol O scale 08 being such an example.

It is a slight variation of my reply in the Dapol 08 thread but may become relevant as further O scale RTR locos are released requiring more than 4 lighting functions and where the manufacturer has used the MTC21 connector to enable the loco to be DCC ready.

MTC21 is the connector which has NMRA approval and NEM recognition. Therefore by default all 21 pin decoders are MTC compliant and will drive the loco and at least 4 function outputs. However, a MTC21 pin decoder will only operate 6 function outputs provided it has the connections to allow it to do so.

Beware - OEM installed decoders may have their function outputs reduced further to suit the loco.

I have checked the latest respective manuals for the common sound decoders used for British locos - ESU Loksound V4.0 and Zimo.

On the ESU Loksound V4 pins 2, 3 (wheel sensors) and 17 (motor 3) have no connection whereas they do on the Zimo Mx644D for functions 5 and 6. Therefore the Zimo decoder has 6 function outputs which is the recommended decoder for the Dapol 08.

This unfortunately means checking the decoder specifications before selecting the desired decoder.

I also checked the NEM 2011 Electrical Interface Recommendation and NMRA Recommended Practices (RP-9 1.1) just to be certain.

The extracts below are from the ESU and Zimo manuals which are unfortunately not orientated in the same direction for an immediate visual comparison.

Loksound V4.0

Zimo MX644D. Note this does not have a blank index pin but a ground instead. Take care when installing.

I haven't checked the Loksound V4.0XL yet to see how many lighting functions it can support as I know these are commonly used in Heljan O diesels.

 

[Ressaldar]

Hi Dave,

the comparison of a Zimo MX644D with the Loksound V4.0XL in connection with Heljan diesels is wrong - the correct comparison would be with a Zimo MX695. The continuous rating for the MX644D is only 1.2A.

cheers

Mike

 

[Yorkshire Dave]

Thanks for the Zimo pointer Mike. I need to have a look as I may end up with the XL4.0 or Zimo equivalent in my GP9 which has a large Pittman motor.

 

[richard carr]

Dave

Thanks for pointing that out. I'll be trying my first Zimo decoder in my 08

The ESU Loksound V4 XL, isn't really relevant to the discussion, as it is not a 21 pin compatible decoder, it has screw terminals.

Richard

 

[richard_t]

The other thing to watch out for on the Dapol 08 with an ESU 21MTC LokSound, for example, is that AUX3 is only "logic" level, and won't have enough power to control the shunting lights, so you'll need an amplifier add-on board if you have one of these decoders. It's also the wrong polarity, as function outputs are usually 0v when on, and track voltage when off, but the logic outputs are >2V, when on, and <0.4V when off.

ESU do an adapter board, as well as others, this for example. I have a simple design with a PCB manufacturer at the mo, but it's likely to be a good couple of weeks before I get it back.

More details here: SBS4DCC - The Infamous 21MTC Interface Connector

 

[TheSnapper]

AtachedOTE="richard carr, post: 142612, member: 131"]...........I'll be trying my first Zimo decoder in my 08..........Richard[/QUOTE]

Good man!

Paul Chetter has supplied me with the following information:

"The two problems with Loksound are:
1) because of the components on the PCB and the thickness of loksound decoders, they do not physically fit properly
2) it will cause the rear lights to remain permanently on, unable to switch off. (same problem with all 21MTC decoders, sound or otherwise).

ZIMO MX644D is a 21 pin decoder for which the Dapol has been designed. It is not an MTC decoder so will work all lights correctly"

Attached are the User Notes for the project he has prepared especially for this loco

Contact Paul for more details at soundsloco@btinternet.com

(Usual disclaimer again: I have no commercial connection, just a happy customer!)

Cheers
Tim

 

[Yorkshire Dave]

2) it will cause the rear lights to remain permanently on, unable to switch off. (same problem with all 21MTC decoders, sound or otherwise).

The other thing to watch out for on the Dapol 08 with an ESU 21MTC LokSound, for example, is that AUX3 is only "logic" level, and won't have enough power to control the shunting lights, so you'll need an amplifier add-on board if you have one of these decoders. It's also the wrong polarity, as function outputs are usually 0v when on, and track voltage when off, but the logic outputs are >2V, when on, and <0.4V when off.

Thanks for this Tim/Richard. This is the info I was trying to obtain.

1) because of the components on the PCB and the thickness of loksound decoders, they do not physically fit properly

This point begs the question for any manufacturer fitting a DCC ready circuit board - why not design the circuit boards to accept most manufacturers decoders rather than just one, otherwise it harks back to the days of Henry Ford 'You can have any colour as long as it's black'.

 

[SoundsLoco]

Dave

I'll be trying my first Zimo decoder in my 08

Richard

And your second in an LLC Class 15 ?

If you view the Dapol 08 video I posted elsewhere, you will glimpse the Class 15 in the background. I was also showing that model with sound at the Spalding Show last weekend.

Lots of very favourable comments, not bad for a non-specialist show.

You will also find that the LLC model does not suffer from the decoder incompatibility problems the Dapol 08 has exhibited.

Paul