Zimo MX644D and LED's

[bigal10]

Hi Folks,

 

I have been trying to get to grips with LED lighting in a number of my Loco's and I notice that Zimo state in their Kleine Decoder Manual, that the MX644D (21pin) has 2 SUSI outputs that apparently can be used as LED functions, without the use of resistors, as they are built into that particular decoder (only). And by use of CV 124, Bit 7 =1 that makes them into LED outputs.

 

I understand that the LED should then be wired to Decoder Negative pole, according to Zimo's Web Page.

 

My question is, which Function outputs would they be?

 

Has anyone done this? - I'm thinking of using this on a Bachmann Class 20, which has precious little room inside, and the lack of resistors inside the loco would be useful !

 

Regards,

 

Alan.

[Nigelcliffe]

( I'll start this by saying I've not re-read the manuals for the 644D to specifically answer this).

 

With many Zimo decoders, there are two outputs with multiple capabilities; they can be Susi (for talking to an external sound decoder, such as those from Dietz), servo control, or additional logic-level function outputs.   What those outputs do is set with a CV. 

 

Having set them to Logic Level, they provide 5v, but with a very strict and low current limit of 10mA.  Exceed the current and "pfff" goes the decoder output, no warning, no protection.   So, use of them needs to be with caution.    LEDs are NOT 5v devices, they have a voltage drop over them,  and will draw whatever current they can (so your unprotected decoder output goes "pfff").  The purpose of a resistor is to limit the current into the LED, protecting both the LED and limiting the current to what the supply can deliver.   So, you still need resistors (or other circuitry), and need to do the calculations to work out an appropriate resistor for the situation.    

 

Resistors can be tiny - surface mount ones are a millimetre or so across.   Metal film resistors (with wire legs) are far smaller body sizes than the common carbon film resistors.  

 

If the CV's are set, the logic outputs will be the next available function numbers on the decoder, so for MX644D, that appears to make them function outputs 7 and 8.   Where they are on function keys depends on the decoder function mapping, default mapping puts them on keys 7 and 8, but where they are after the decoder has been programmed with sounds (etc) is down to the sound project writer. 

 

 

 

- Nigel

[Porcy Mane]

Thanks for the concise explanation. You have just saved me a couple of hours deciphering the manual.

 

Porcy