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S88-N Printed Circuit Boards and explanation

S88-N logoS88-N producten


S88-In order to control a modeltrain layout automatically you need to be able to detect the location of a train. For that detection of a train on a piece of track is necessary. Different solutions are available in the market place. Marklin was the first to arrive on the market with its S88 product, based on 'mass'-detection on its 3-rail system. It is based on detection of a non-isolated axle on the track, making a short between the two rails. This is the standard S88 product still on the market by different manufacturers.

Later in time a current sensing detector was added to S88 modules. This was done so 2-rail model railroaders could also use the S88 way of working. A current sensor was added in front of the S88 module. The current sensor, based on a four anti-parallel diode circuit, was put in the power circuit to the track. As soon as a 'power-user' entered the track the current sensor detects it and feeds its information via opto-couplers to the S88 module. This is a standard configuarion in e.g. Viessmann 5233.

All these commercial products also have some drawbacks. The normal S88 bus is based on flat cable connector which are sensible for interference. The Viessmann 5233 can only host one power wire for 8 different track pieces. This is annonying in controlling turntables or via more than one boosters powering the layout. S88 is based on x times 16 connections, while the 5233 only has 8 in them. You're forced to buy them in pairs. The price of the commercial products is quite high too.

Reasons enough to develop something ourselves. Huib Maaskant and I developed the BMD16-SD in 2005, based on current sensors, S88 interfaces and a connector based on RJ45 and UTP cables. This was followed in the first half of 2008 by the second, enhanced, version of it called the BMD16-SD2 and July 2008 this was followed by the third version, now called BMD16N-SD and its brother BMD16N. De letter N is quite important. The new PCBs now have a standardized interface for UTP cables, called S88-N, as standardized by OpenDCC.

In order to connect the BMD16N and BMD16N-SD to regular S88 products we also developed a S88-N adapter set. This set consists of two small PCBs in order to connect S88 to S88-N and vice versa. These three products (BMD16N-SD, BMD16N and S88-N adapter set) can be obtained as PCB, building set and on special request as fully soldered and tested products.

All three products can be obtained using the following link: Orderform for S88-N products

The three products are described extensively on this page:
  1. BMD16N-SD
  2. BMD16N
  3. S88-N adapter set


1. BMD16N-SD: 16 fold current sensing detector with S88 and S88-N interfaces

De BMD16N-SDS88-N logo

As said the BMD16N-SD is a train detector based on current sensing with S88 and S88-N interfaces. This product is versatile in use, as well with normal S88 connectors and cables as well as via the new S88-N connectors and UTP cables.

The decoder has current sensing technology build-in as designed for the Viessmann 5233 and is compatible with the S88 bus. It can be used for a.o. Märklin Digital, Uhlenbrock Intellibox, Fleischmann TwinCenter and the LDT HSI-88.

The BMD16N-SD is connected to the e.g. Intellibox using the S88 connector/cable combination or via the S88-N adapterset. The connections between the different BMD16N-SDs is made using standard UTP CAT5 cables with can be bought in may shops and make yourself. I already used cablelengths of over 5 metres without any problem. The reason for working fine is the twisting in pairs of the UTP cable making it much less vulnerable for interference.

 

BMD16N-SD1 BMD16N-SD2
The BMD16N-SD can be used in two different configurations:
  • The first method (left) uses screwing connectors and has a configuration comparable to two Viessmann 5233's (1 power supply for 8 detectors)
  • The second method (right) uses printconnectors and has a configuration of 16 fully independent current sensing detectors. All 16 have a seperate power supply.

A more experienced user can change the first configuration to the second for one or more detectors very easily.

interconnectie BMD16N-SDconnectie met IBconnectie S88-N

printplaat BMD16N-SDAbove three photographs show the connectors of the BMD16N-SD. The photo on the left shows a direct interconnect from on BMD16N-SD to another using the side-to-side connector on the PCB. The photo in the middle shows the S88-N coonection to the Intellibox using the S88-N adapterset. The photo on the right shows the connection to the print of standard UTP cables for the S88-N interfaces.

We deliver the PCBs for all this as shown on the left. They are delivered together with a comprehensive user guide to help you make your own BMD16N-SD and how to use them.

The different electronic parts can be ordered by e.g. Conrad. You can also visit your local shop. This way it is possible to make a BMD16N-SD for around € 45,- (excluding mail delivery). That's almost 50% cheaper compared to regular commercial products. To save even more money you can leave out the IC sockets.

Parts
Count Description Conrad number
16 resistor 47 Ohm 403881 (100 pieces)
1 resistor 330 Ohm* 403199
1 resistor 1 kilo Ohm 403253
17 resistor 10 kilo Ohm 404160 (100 pieces)
2 resistor 100 kilo Ohm 403490
1 resistor 220 kilo Ohm 403539
16 rectifier B80C1500 501441
1 LED 3 mm 184713
1 capacitor 100nF 453358
1 capacitor 100pF 451746
1 transistor BC517 154695
10 16 pin IC socket** 189529
4 ILQ620 optocoupler 153612
4 IC 4044 172871
2 IC 4014 172707
6 3-pole screw connector*** 729957
2 connector strip**** 732478
2 RJ45 western connector 716148

* If you connect the BMD16N-SD to +12 Volts, you have to use a 1 kilo Ohm resistor instead.
** Only needed if you want to mount the ICs in sockets.
*** You can only choose screw connectors if you plan to use the contacts in two groups of 8.
**** You only need one if you are fitting the board with screw connectors.

You do not have to be a soldering virtuoso to assemble a BMD16N-SD, but some experience is advisable. The manual will guide you through the assembly step by step. The rectifiers on the board are suited for any H0 scale layout or smaller. They will also work in O scale, unless you are operating locomotives with really big power-consuming engines. In that case I would recommend replacing the rectifiers with bigger ones.

grafische weergave

The feedback decoders are connected to the central unit as a chain. The order of the decoders determines how the contacts are numbered. The first decoder has contacts 1 to 16, the second one 17 to 32, etc. You can connect up to 31 decoders with 16 contacts to the S88-bus.

grafische weergave

The BMD16N-SD is typically inserted in the red wire running from the central unit or the booster to the track. The wire connects the input of the decoder with the output of the central unit or the booster. A second wires connects the output of the decoder with the right rail. The left rail is connected directly with the central unit or the booster via a brown or a black wire. You use a different contact for each feedback section (occupancy detector). The BMD16N-SD allows you to connect each contact to another power source.

grafische weergave

The option to connect each contact to another power source comes in handy with e.g. a reversing loop. The reversing loop module has to be connected between the central unit and the feedback decoder. The module uses some power itself and if yo were to insert between the feedback decoder and the rails, the decoder would signal the track as ‘occupied’. The inputs of the contacts inside the reversing loop (which can be as many as you want) are simply connected to the reversing loop module. The outputs are connected to the track.

You can download the user guide from here: acrobat readerBMD16N-SD.en.pdf

BMD16N-SD Features

  • Integrated feed back decoder with 16 contacts with current detection for the S88-bus
  • Suited for all 2-rail model railroads, gauge 0 to Z
  • Compatible with a.o. Märklin Digital, Uhlenbrock Intellibox, Fleischmann Twin-Center and LDT HSI-88
  • Compatible with the s88-N standard and all other s88-N equipment
  • Connect the S88-bus via standard S88 cables or reliable network cables
  • Other BMD16N/BMD16N-SD decoders can be directly connected sideways
  • Even further reduced risk of errors thanks to filtered clock circuit and improved reset circuit
  • Contacts can be configured in 2 groups of 8, 16 independent contacts or any combination of the above
  • Choice between inexpensive print connectors or sturdy screw connectors
  • Easy to assemble for everyone with some soldering experience
  • Extensive manual with step by step assembly plan

-> Orderform for S88-N products


2. BMD16N: 16 fold track occupancy detector based on mass-detection with S88 and S88-N interfaces
BMD16NS88-N logo

The BMD16N is a track occupancy detector based on 'mass' detection with S88 and S88-N interfaces. These features makes it a versatile product. It can be used in S88 configurations with S88 cables as well as with S88-N interfaces and UTP cabled networks.

The decoder is fully compatible with S88 bus products. It can be used with e.g. Märklin Digital, Uhlenbrock Intellibox, Fleischmann Twin Centre and LDT HSI-88.

The BMD16N is connected to the e.g. Intellibox by the S88 connector/cable combination or via the S88-N adapterset.

 

BMD16N stekkers

 

The connections between the different BMD16Ns is made using standard UTP CAT5 cables with can be bought in may shops and make yourself. I already used cablelengths of over 5 metres without any problem. The reason for working fine is the twisting in pairs of the UTP cable making it much less vulnerable for interference.

De BMD16N is connected to the to be detected track sections using screw connectors as shown on the photograph on the right. The connections to the S88-N bus are made using RJ45 connectors and the connections to the S88 bus are made using 6 folds print connectors (left and right on the back of the PCB)

Below three photographs show the connectors of the BMD16N. The photo on the left shows a direct interconnect from on BMD16N to another using the side-to-side connector on the PCB. The photo in the middle shows the S88-N coonection to the Intellibox using the S88-N adapterset. The photo on the right shows the connection to the print of standard UTP cables for the S88-N interfaces.

 

interconnectie BMD16N-SDaansluiten IBconnectie S88-N

BMD16N printplaat

We deliver the PCBs for all this as shown on the left. They are delivered together with a comprehensive user guide to help you make your own BMD16N-SD and how to use them.

The different electronic parts can be ordered by e.g. Conrad. You can also visit your local shop. The product is much cheaper compared to commercial products in the shops. To save even more money you can leave out the IC sockets.

The BMD16N is compabtible with all other products on the market using the S88-N logo.

Parts
Count Description Conrad number
1 resistor 330 Ohm* 403199
1 resistor 1 kilo Ohm 403253
17 resistor 10 kilo Ohm 404160 (100 pieces)
2 resistor 100 kilo Ohm 403490
1 resistor 220 kilo Ohm 403539
4 resistor network 4 x 100 kilo Ohm 416053
16 capacitor 10nF 453323
1 capacitor 100nF 453358
1 capacitor 100pF 451746
1 LED 3 mm 184713
1 transistor BC517 154695
6 16 pin IC socket** 189529
4 IC 4044 172871
2 IC 4014 172707
6 3-pole screw connector 729957
1 connector strip 732478
2 RJ45 western connector 716148

* If you connect the BMD16N to +12 Volts, you have to use a 1 kilo Ohm resistor instead.
** Only needed if you want to mount the ICs in sockets.

aansluiten

The feedback decoders are connected to the central unit as a chain. The order of the decoders determines how the contacts are numbered. The first decoder has contacts 1 to 16, the second one 17 to 32, etc. You can connect up to 31 decoders with 16 contacts to the S88-bus.

aansluiten IB II

If you own a 3-rail layout, you will probably use the BMD16N for occupancy detection via ground detection. This is by far the easiest and most reliable way to know where your trains are. You could also use reed contacts or special contact tracks, but these are less reliable and they do not generate a permanent signal for an occupied track. You cannot use these options to detect e.g. a car left behind. Furthermore, you can connect ordinary switches to the BMD16, for example for a layout plan track control or a emergency stop switch.

The user manual can be downloaded here: acrobat readerBMD16N.en.pdf

BMD16N Features

  • Improved feed back decoder with 16 contacts for the S88-bus
  • Suited for all model railroads, gauge II to Z
  • Compatible with a.o. Märklin Digital, Uhlenbrock Intellibox, Fleischmann Twin-Center and LDT HSI-88
  • Compatible with the s88-N standard and all other s88-N equipment
  • Connect the S88-bus via standard S88 cables or reliable network cables
  • Other BMD16N/BMD16N-SD decoders can be directly connected sideways
  • Even further reduced risk of errors thanks to filtered clock circuit and improved reset circuit
  • Sturdy screw connectors
  • Easy to assemble for everyone with some soldering experience
  • Extensive printed manual with step by step assembly plan

-> Orderform for S88-N products


3. S88-N adapterset

S88-N verloopsetS88-N logo

To connect S88 connectors to S88-N connectors/cables Huib Maaskant and I developed an adapter set to finish off the S88-N based product line (BMD16N-SD, BMD16N and S88-N adapter set). The set comprises two small PCBs holding an S88 to S88-N adapter (e.g. for connecting the Intellibox to S88-N UTP cables) and a S88-N to S88 adapter to e.g. connect old S88 devices to the S88-N bus .

On the small PCB a RJ45 connector is soldered (Conrad ordernumber 716148). On the other side a piece of a strip connector is soldered horizontally or vertically (Conrad ordernumber 736368).

Below two photographs are shown with usability options. The photo on the left shows the mounting of the adapter on the S88 interface (in this case on a BMD16N), the photo on the right shows a Viessmann 5217 with a S88-N adapter on both sides, hence giving S88-N interfaces to this S88 product.

s88-n adapter op bmd16nadapter op 5233S88-N towards IB

S88-N and BMD16-SD(2)

The connections of the S88-N bus are NOT equal to the ones of the predecessor prints BMD16-SD and BMD16-SD2. Despite both using an RJ45 connector and UTP cables, you cannot interlink the BMD16-SD(2) to the BMD16N(-SD) without adaptor. We have developed the S88-N adapter set to connect any S88 product (also available on BMD16-SD(2)!!) to S88-N products. So you can interlink the BMD16-SD(2) to the BMD16N(-SD) by using the S88-N adapter set. When you want to make an interface you own, the table below is of help:

s88-N wiring standard
RJ45 pen Color in UTP cable s88-N, BMD16N, BMD16N-SD
1 Orange-white +5V/+12V
2 Orange Data
3 Green-white GND
4 Blue Clock
5 Blue-white GND
6 Green Load
7 Brown-white Reset
8 Brown Railsignaal

-> Orderform for S88-N products

We are still able to deliver the BMD16-SD2 PCB. For a description of the BMD16-SD2: : click here