Separate Accessory BUS wiring

[ColinB]

Yes, I looked at their site. They have lots of hardware but it appears you have to be a member to buy it. It appears reading the data on the web page that they use 125 kBaud for the speed which is what we used to use in the vehicles for the low speed bus ( most vehicles have two buses) and I have a ton of tools that can read it. Looking at the hardware they have made it all looks really good. I don't know if they have aready done it but if you had a DCC to CAN interface board, then the system would work with all existing tools. So the accessory command in DCC calls up the relevant point via CAN. 

[Flashbang]

Hi

Yes you do have to join MERG to obtain their kits etc The cost is £16 pa plus a one off £5 joining fee. IMO its well worth joining even if its just for the information they provide.

I don't see the point (No pun intended)  in calling up a DCC command to operate an item via CBUS? Though this can be done I understand (Not proved by myself).

You can obtain all sorts of DCC accessory decoders that work over the two wire DCC Bus pair, such as for an example.... Solenoid point motor control or Stall motors control etc.   

CBUS works over its own dedicated twisted pair of data wires, plus a 12 volt regulated power supply to feed all the CBUS modules. Plus it provides feed back over the same pair of wires   A lot different to DCC and CBUS does not provide traction power.

Why would you want to mix the two, when both work happily independently? But as I've said, I believe you can do so with suitable module??

 

However, none of this has anything to do with the OPs question re a dual DCC bus.

[ColinB]

The only reason you would want a DCC to CBUS is if you were trying to interface the system with something like Railtrack. I don't use Railtrack, but I assume when Railtrack asks for a point change it will issue a DCC Accessory command. That is the only reason.   

[menacesco]

Chrissaf could you give me a steer on the correct way to wire up the relay board you recommended to the R8247 accessory decoder and point motors please?

 

regards. 

[Chrissaf]

You'll have to ask Rob [RAF96] that question. He is the one that has practical physical experience of the suggested relay board sold via eBay. Rob gave a link to his website, in a previous post. I duplicate it below. The board is wired as per Fig 4 on his web page. Unfortunately, the image quality is rather poor. Maybe Rob can reproduce Fig 4 again in this thread at a higher resolution. I will ask him.

 

EDIT: Rob has responded to my email and says he will look at this tomorrow.

 

http://www.halton96th.org.uk/relay-module.html

 

It's not made 'crystal clear' on the web page, but the board needs to be powered by a +5 volts DC power supply, else it won't work. This power supply is a separate one from the power supply used for the CDU and it definitely cannot be fed by DCC voltage.

 

Note also Rob's note in the supporting text on his website regarding power 'link' positions on the board. The positive output of the R8247 [C terminal] needs to be isolated from the positive supply rail [VCC] on the relay board. This is the link function his text note relates to.

 

Note also that that only one R8247 C terminal needs to be wired to the relay board. All the C terminals are common within the R8247 decoder so don't need to be individually extended to the relay board. Thus only the four port + & - terminals of the the R8247 plus one C terminal are wired to the Relay board.

 

My own board was built by me to my own design, so won't be applicable to the eBay board.

[96RAF]

The original figures are on the PC which is shut down at present.

I will crank it up tomorrow and post a better picture.

I will also rework the article to force the authoring software not to ‘optimise picture for the web’.

Just be aware these relay modules can be slightly different so check the one you buy meets your exact requirements with regard to relay voltage, trigger level logic, ability to power the board and triggering at the correct voltage, ability to cope with DC load, etc. I bought three before I got one that works with R8247 and a CDU after a fashion.

[menacesco]

Thank you both very much. That looks very clear. I am nervously looking forward to starting this project. I'll let you know how I get on. Regards. 

[Chrissaf]

After some late night email dialogue with Rob to get details. I have put together this information on Rob's behalf to save time.

 

Wiring the R8247 Accessory Decoder side of the Relay board.

 

The best engineering solution in order to make connections between R8247 and relay board is to make up a wiring harness between the R8247 Accessory Decoder and the Relay board using industry standard DuPont 2.54mm Female Housing connectors. The currents on these input pins are very low, so only thin wires are needed which will aid the termination on the DuPont female terminals. Wire of 7/0.2mm size should suffice. The wires are best crimped onto the terminals using very small fine pointed tipped long nose pliers. It is fiddly, but can be done with care and practice. I have done loads myself, as I make extensive use of these DuPont connectors.

 

Two housings are required. A 9 way housing [1*9] for the relay inputs and a 3 way housing [1*3] for the +5 volt DC power supply.

 

These housings and female terminating pins can be purchased here. Be careful if you source the DuPont housings elsewhere, as normally you have to buy the crimp terminals separately. The linked eBay seller includes the crimps in the listing.

 

The harness is made up as per the graphic below.

 

/media/tinymce_upload/0ce834f648a978176a68aa2185ae5490.jpg

 

The output [relay contacts] side of the relay board are wired up as per the schematic below:

 

/media/tinymce_upload/3681aabbb7c27345ba43c994972f8b83.jpg

[Chrissaf]

My original schematic post now updated to reflect the corrections suggested by Rob to me this morning after reviewing my original post I published last night. The original post from last night has been removed and replaced by a new one this morning.

 

The Relays on the board used in the schematic are 5 volt relays not 12 volt. So the +5 volt DC input supply is used. The board in the graphic is the board linked to in the eBay seller link on Page 2 of this thread and the sellers listing states +5 volt DC operation.

 

/media/tinymce_upload/7bd94815a8a5b57ba981e6169fde0473.jpg

[96RAF]

Thanks to Chris for the amendment.

 

If the relays are 12v on the module then DC-In should be 12v (my relay board and the pictured module have 5v relays). The jumper as stated is removed to separate JD-Vcc and Vcc. Note you then need a three way housing with the centre pin omitted.

 

If the jumper is left on the module DC-In is generated by Vcc of 5v at the trigger header from an external control circuit such as an Arduino or RasPi.

 

Note that all ‘C‘ terminals are connected together inside the R8247 so only one wire is required on the trigger header to Vcc. Although there is a standing positive of 14vDC on the ‘C‘ terminal this is not realised at the relay module until the floating IN1-8 triggers are pulsed from the R8247 to make switched negatives.

[Chrissaf]

@menacesco.

 

Since the schematics posted last night have been amended since your last post above. Could you please indicate that you have seen and noted the amendments.

 

Thank you.

[menacesco]

Hi Chrissaf,

I've read the post and adjusted my connector order to match the 5volt version which I have. I already have a 5v 0.2amp supply from an old piece if equipment. Is this suitable to power the relay boards.

[Chrissaf]

5 volts DC at 0.2 amps [200mA] is more than enough. The relay board is designed to be used with an Arduino or PI programmable processor board with the relay board getting its power from the same 5 volt input used to power the processor. These processor boards are typically powered by a computer USB port, thus the relay board current draw is likely to be measured in the low mA current range.

 

Thank you for replying, I can now stop bumping this thread and let it slip naturally down the rankings.

[menacesco]

Hi Chrissaf,

I have created my first board and wired the R2847 to the relay board, however, I am having difficulty understanding the output side wiring.

I obviously have 2 relays per point - solenoid motor - with 6 connection points and 3 wires coming from the point motor? I cannot work out which connection points the 3 wires - red, green and black - should go to.

Apologies for my ignorance!

[menacesco]

Thanks Chrissaf. I can understand your picture above except for some confusion in my mind over the CDU. Is this the R2847?

[menacesco]

Chrissaf and RAF96.

I think I have worked it out now. I did not realise I needed a separate CDU unit. Stupid me!

I will have 8 x R2847 units for my layout. Will one CDU be sufficient and could you recommend one please?

Regards

[Flashbang]

No the R8247 is the Hornby DCC Accessory decoder.

Hornby do not make a CDU.  You would have to source this from elsewhere. - Peco, Block Signalling   Brimal to name but three There are many others and eBay can be a source too

Plus there is the need for a suitable power supply to feed the CDU and all motors. Typically this is 16volts AC at around 1.0Amp. But can also be a DC supply at around 19 to 21 volts (ex laptop PSU are often used)

[Chrissaf]

The black wires from the point motors do not go to the relay board. They are all commoned together and go to the negative side of the CDU output. Only the red and green wires of the point motors go to the relay board. The positive side of the CDU output connects to all the relay contact levers. All point motor wiring should IMO use a minimum 16/0.2mm wire thickness.

 

The drawing below demonstrates the above text.

 

Note for all readers. The colours used in the drawing below relate only to Hornby point motors. PECO use the same three colours, but PECO use Green and not Black as the common return.

 

/media/tinymce_upload/8ba249e49de75c6cd88498ca33611410.jpg

 

           My drawing above should resolve all outstanding misunderstanding.

[Chrissaf]

As you have already realised. The R8247 is not the CDU in the drawing. The CDU and the power supply are completely separate items from the R8247 and completely outside the Hornby product portfolio.

 

A CDU is a shared resource, so yes only one is needed. CDUs can be sourced from lots of sellers. The Gaugemaster one is the one that is usually mentioned in this forum, but this one is quite pricey for what it is. Better value can be obtained using eBay.

 

https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=CDU&_sacat=0

 

This RKcdu2 one is particularly powerful and has been given a good review by other Hornby forum members that have used it. This one also has the benefit of having a 2.1mm DC Coax power in connector, so [with luck] may match the connector used on a DC power pack documented below. It also has a screw terminal power input connection as well for alternative powering up convenience.

 

You haven't asked yet, so I am just pre-empting your next unasked question. The power supply feeding the CDU can either be an AC transformer with an output of 16 volts AC at 1 amp. Or it can be an ex Laptop 19 volt DC power pack rated at about 3 or 4 amps. The 19 volt DC Laptop power supply is the easier one of the two to source and can be purchased cheaply on eBay. The current of the power supply is not super critical as it is the CDU itself that generates the high current required by the Solenoids.

 

EDIT: Flashbang just beat me to the draw and posted whilst I was busy searching eBay and typing my reply.

 

EDIT 2: "RKcdu2 one" link above updated to a 'Ready Made' version rather than a 'Self Build Kit' .... see post further below that references this. For any reader who would prefer the 'Self Build Kit' then this is the original URL link for it.

 

[96RAF]

Just to be totally clear.

The relays are introduced purely to allow a CDU to be used for extra oomph and to keep the DCC side (R8247) well away from the DC side (CDU).

[menacesco]

Thanks again guys. I totally get it now. CDU and power supply ordered. Cheers. 

[Chrissaf]

Oops confession time.

 

I have only just realised that the RKcdu2 link I provided, is for a 'self build kit'. This in itself isn't a big deal unless soldering components on a PCB is totally beyond the user. The instructions for building this kit are provided as a PDF download and do not appear to be shipped [according to the eBay listing] with the kit. A 'Ready Made' version is available on the site below for 50 pence more than their kit version.

 

The downloadable documentation links are found on the RK Education website:

 

Direct Link to construction documentation. Below is some crucial information not adequately covered in the download documentation.

 

Note that the Capacitors are polarity sensitive and MUST be fitted the correct way round. The TIP41A Power Transistor also needs to be fitted the correct way round as does the Bridge Rectifier [bR1] and Diodes [D1 & D2]. The LONG LEG of the LED [Diode D1] is the positive side. The 'bar' embossed on the end of the Diode D2 case is the positive end of the diode. The Bridge Rectifier [bR1] LONG LEG is the positive leg [it is also marked + on the case].

 

[96RAF]

Brimal.co.uk also does various ‘strength’ CDUs but their site still appears to be down during a server move.

[menacesco]

Dear Chrissaf and RAF96,

Having received the last of my components today I completed my test bed and I am pleased to report that, after a few hiccups, everything is now working well. I am feeling quite pleased with myself and I am looking forward to now setting up all 8 accessory decoders. However, my success would not have been possible without you two guys. Many, many thanks again.

[Chrissaf]

😎