Model train decoder
A model train decoder is a decoder component of the digital model train control that converts the standardized digital control commands into the corresponding analog circuits.
In addition to the large model railway manufacturers, there are some smaller companies that have specialized in the production of these components or that supply the manufacturers with them.
Because of the differences in specifications in the two large systems DCC and Märklin-Motorola (MM) , the decoders are also different. There are central units that support both systems, at least with the accessory decoders, by simply sending all commands twice (e.g. Roco Multimaus). Some decoders also accept both formats or can be set using jumpers . Otherwise the decoder must match the central unit.
A distinction is made between different types depending on the component to be controlled.
Locomotive decoder
In the case of the analog model railroad, the locomotive receives the correspondingly regulated traction current through the rails, only the light may be switched "on board". In the digital model railway, the locomotive decoder takes on the role of the locomotive driver, as in the original, directly in the locomotive by processing the digital signals taken from the rails and distributing the constant drive current accordingly to the motors and additional functions. As in the prototype, a constant voltage is available to all vehicles along the entire route, so the Locdecoder can switch functions (e.g. the lights) even when the vehicle is stationary.
In addition to the differentiation according to the type of communication, this also results in the distinction between direct and alternating current systems. In the meantime, however, most decoders work automatically with the DCC and MM protocol. A big difference between the two protocols is the number of possible speed steps that can be set: MM: 14/27, DCC: 14/28/128. In any case, the power supply cannot be switched, so that the manufacturers always have their own types for direct and alternating current.
Many vehicle manufacturers do not deliver their own decoders and leave it to the buyer to install the modules as required. To this end, all new locomotives will be equipped with a standardized NEM interface. Locomotives are wired in such a way that they can also be operated analogue without a decoder by means of a bridge plug on the NEM interface. If a decoder is installed, the motors and lamps are controlled via this.
The assignment of the contacts and the recommended cable colors for the 8-pin decoder connector are defined as follows according to NEM-652:
| pin code | description | colour | pin code | description | colour |
|---|---|---|---|---|---|
| 1 | Motor connection on the right | orange | 8th | Right pantograph | red |
| 2 | Rear lighting | yellow | 7th | Positive pole for consumers | blue |
| 3 | Additional function F1 | green | 6th | Front lighting | White |
| 4th | Pantograph on the left | black | 5 | Motor connection on the left | Gray |
The current decoders are also able to recognize analogue controls independently and to forward them 1: 1. This is also possible during operation, so that the combination of analog and digitized system parts is possible. To do this, however, a transition piece is required in the route, which ensures that both circuits remain separate even with long locomotives.
By default, the motors are regulated and the driving lights, which can be switched on and off, are controlled depending on the direction. Depending on the range of functions, additional functions can be switched: clutches, sound modules, etc.
Setting (programming)
So that the commands arrive at the correct locomotive, each decoder has its own address at which it can be reached. With old decoders this is set with jumpers, with newer decoders it is set manually via the control center or in some cases automatically. The standard address after the first start-up is usually 3. Other properties of the locomotive decoder can also be parameterized so that certain driving properties of locomotives can be realistically simulated. These include B. Acceleration and deceleration. While the speed changes have an immediate effect with an analog control, digital decoders react to a speed step command according to the set acceleration rate with a correspondingly delayed speed change. This means that a model of a steam locomotive starts moving more slowly than a replica of a TGV with the same speed command without the intervention of the control center . Minimum and maximum speed, brightness of the lighting and the additional functions can also be changed. One speaks wrongly of the "programming" of the decoder, but only individual register values are set, the program logic of the decoder is fixed. These adjustable register locations are called configuration variables, or CVs for short. Each CV has a certain function that behaves depending on the value stored in it. Programming can either be done specifically on a locomotive on the layout or on the programming track. All settings, including those of the address, can be changed on the programming track, but all vehicles on the track are affected. With the "Programming on the main track" (POM) method, the locomotive is addressed directly with the address and adjusted independently of the others, but in this case it is not possible to change the address. As confirmation of a programming command, the decoder reacts with a flashing light output or in some cases with a short motor impulse ("twitch").
According to the NMRA, the most important and generally applicable CVs are:
| CV | values | default | meaning | Specialty |
|---|---|---|---|---|
| 1 | 0-127 | 3 | address | with some decoders only up to 99 |
| 2 | 0-255 | - | Starting voltage | Voltage at speed step 1 |
| 3 | 0-255 | - | acceleration | Waiting time until the next higher speed step |
| 4th | 0-255 | - | Deceleration (braking rate) | Waiting time until the next lower speed step |
| 5 | 0-255 | 0 | Maximum voltage | Voltage at the highest speed level (maximum speed) |
| 6th | 0-255 | 1 | Medium tension | Voltage at medium speed (medium speed) |
| 7th | 1 - 255 | - | Version number | just read |
| 8th | 0-255 | - | Manufacturer number | Setting a certain value triggers a reset (depending on the manufacturer) |
| 9 | 0-255 | 0 | PWM period | Value for the pulse width modulation (motor property) |
| 17.18 | 1 - 10239 | - | long address | Value for the extended or long address |
| 19th | 0-127 | - | Consist address | Activation of long address, multiple traction |
| 28 | 0-255 | - | BiDi | Values for bidirectional communication |
| 29 | 0-255 | - | configuration | Direction of travel, number of speed steps, analog operation ... |
This is followed by values for setting the functions and individual speed characteristics. Even if the standard CV numbers are defined, each decoder uses different setting values for certain CVs, e.g. B. for the speed values.
Conversion (subsequent digitization)
Since an analog and a digital locomotive work electrically in the same way, it is also possible to convert old analog models to digital control if the motors are not too old. Make sure that the maximum power consumption that the decoder can handle is not exceeded. Depending on the model, a place for the decoder must first be found or created by sanding down weight weights.
The connection is made between the pantograph and the motor (s) or lamps. A problem with old models can be that in the past there was often an electrical ground to which both a pantograph, a motor contact and a light contact were directly connected. With direct current locomotives, the light is often changed by simple diodes that switch the lights on and off depending on the direction of travel. Depending on the decoder, it may be necessary to separate consumers and supply lines. If this is the case, the common ground must be resolved by isolating the individual circuits. Sometimes the motor or a pantograph is so inseparably connected to earth by current-carrying connections that the circuit for the earth is thereby given. It may also be necessary to replace metallic fastening material with plastic parts. In any case, diodes for the lighting have to be removed, since the decoder is now used for control; Whether existing coils have to be removed for interference suppression depends on the type of decoder. If a decoder can control its function outputs with a common ground, then this is on one of the supply lines (black). In this case, the common return line (blue) must not be connected. However, such a common ground leads to flickering in the connected lighting when driving, since the fluctuations in the power transmission have a direct effect on the light sources. These fluctuations only occur with control in Motorola format and are therefore called "Motorola flickering". A completely isolated lighting using the common (blue) return conductor avoids this problem. Please note that short circuits due to poor wiring or insufficient insulation can destroy the decoder. Even if many decoders are equipped with overload protection, not all outputs are protected.
It should also be taken into account that decoders get warm when they are loaded and this heat must also be dissipated. Otherwise, the plastic parts of the housing may overheat and / or deform.
Accessory decoder
Decoders for accessories hang on the same data bus as the locomotive control, but use their own address range. In general, addresses are assigned in blocks of four. The module addresses start with 1, each module has 4 ports with two outputs (gates) each, which can have 2 states (ON / OFF). The designations RED and GREEN are also used for the gates, as they are common on the old turnout switches. Depending on the control center, the addresses are addressed on different levels. The direct port address (PADA) is usually displayed on the control units, flat addressing (FADA) is rarely used. Only in the system from Lenz Digital, which is also used by Roco , does the module address begin with 0. This means that the addresses are shifted by 4 ports when accessing other central units.
Example for addressing the 2nd gate of the 2nd port in the 1st module and the 1st gate of the 4th port in the 2nd module depending on the access level used:
| Addressing of the individual modules | according to NMRA | MADA (module) | PADA (port) | Lenz (port) * | FADA (flat) | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Module 1 | Module 2 | 1 | 2 | 1 | 2 | 1 - 4 | 5 - 8 | 5-8 | 9-12 | 1 - 8 | 9-16 | ||||||||||||||
| Port 0 | Port 1 | Port 2 | Port 3 | Port 0 | Port 1 | Port 2 | Port 3 | 1.1 | 2.3 | 1.2 | 2.4 | 2 | 8th | 6th | 12 | 3 - 4 | 15-16 | ||||||||
| Gate 0 | Gate 1 | Gate 0 | Gate 1 | Gate 0 | Gate 1 | Gate 0 | Gate 1 | Gate 0 | Gate 1 | Gate 0 | Gate 1 | Gate 0 | Gate 1 | Gate 0 | Gate 1 | 1,1,1 | 2,3.0 | 1,2,1 | 2,3.0 | 2.1 | 2.0 | 6.1 | 12.0 | 4th | 15th |
*) Da bei Lenz digital das erste Modul die Nummer 0 hat, wären die zwei in diesem Beispiel bereits das 2. und 3. Modul.
Setting (programming)
Today, the decoder addresses are mostly taught in by putting the decoder into a learning mode. This is done with a button or a jumper. The decoder then takes over the addresses that are in the block of the address to which the following switching command from the control center is sent. To do this, simply use a switch button or similar. pressed. A separate LED or the first connected consumer (switch, signal) flashes as confirmation. The learning mode is then terminated and the address remains stored. The address can be changed as often as required, and the blocks do not have to be assigned continuously.
Some decoders, e.g. B. Open DCC decoders also support programming of CVs, so that special parameters can be set in addition to the address. However, not all control panels support this access to accessory decoders.
connection
The current for the respective switching accessories can, but does not have to be, the same as the control current. Since "digital current" is "expensive" because of the necessary components, it is often advantageous to protect this circuit and to use your own simple transformer for the switching current . If you choose your own digital circuit (booster) for the control current, you can switch off the traction current without losing control of the components.
Most decoders switch off the switching power after a certain period of time, even if there is no off command. However, this is not according to the DCC standard. This is supported by the central units, which repeat an on command as long as the button on the control unit is pressed and do not send an off command.
Some manufacturers equip their turnouts with a built-in decoder, eliminating the need for wiring. Control and switching current come from the rails.
Decoder types
Depending on the area of application, there are separate decoders, which are all addressed in the same way, but have different switching properties.
Solenoid decoder
Solenoid article decoders control articles that switch with a current surge at one output each. Analogue, AC voltage is mostly used for this, decoders send DC voltage because of the electronic components. The 4 addresses are used to supply 8 individual outputs. This means that 4 points with 2 positions or 8 uncouplers can be controlled.
Decoder for motorized turnouts
Motorized turnouts often only have two connections that are polarized. Therefore you need your own decoder type with only 4 pairs of connections. As with solenoid decoders, most turnout decoders also switch off after a certain time, even if there is no OFF command.
Switch decoder
To switch other loads on and off, you need a type of decoder that can switch voltages on and off and that keeps the input open until the off command. Although 8 gates can be switched with 4 addresses, some switching decoders only have 4 bistable relays due to the automatic switch-off , so that only 4 loads can be connected.
Signal decoder
For the control of signals there are special switch decoders that display the correct signal image with one switching command for each signal aspect . Switching takes place smoothly by fading in and out. These decoders can control 2 to 4 signals with 4 to 8 addresses and because of the logic for controlling the individual lamps, they have a program chip that may differ depending on the signal system or country (railway company). Standard decoders support one or two signal pairs (main signal and distant signal on the same mast) with 7 terms. 4 ports for 4 terms are then used for a signal (red = stop, green = free, yellow = slow travel, white = shunting travel). Some decoders are equipped with their own signal bus, which is used to connect several decoders and e.g. B. automatically sets advance signals analogous to main signals .
Special decoders for turntables, transfer platforms, etc.
Separate decoders with the corresponding control logic are available for special processes in complex controlled systems such as turntables and transfer platforms.
In principle, all controls can be made with simple switch decoders, the additional logic (limit switch-off, blanking of pre-signals, turntable control ...) is then done by additional relays, electronics or a computer.
Cable car decoder
In 2012 the Austrian Jägerndorfer Ges.mbH brought out its own decoder for the H0 model cable car it produced. This allows the various functions of the railway to be controlled and various operating noises to be reproduced. Brawa then presented a similar component for their cable cars at the Nuremberg Toy Fair 2013.
Feedback modules
For the reporting of switch positions, occupied tracks and current locations of trains, feedback in the form of contacts is required in a wide variety of ways. Their status is processed by their own modules and sent to the control unit, usually a PC. These components, which are also incorrectly referred to as feedback decoders, are, however, encoders because they convert the analog pulses into digital information. They are also connected to their own bus. The most common type is the S88 feedback bus system .
Individual evidence
- ↑ NEM-652 (PDF; 16 kB), MOROP
- ↑ Configuration variables , OpenDCC
- ↑ Description of the servo decoder (PDF file; 376 kB), Joka electronic company
- ↑ Addressing , Rocrail
- ↑ Cable Car Sounds H0 2012 , Jägerndorfer
- ↑ For summiteers - the Hahnenkammbahn in H0 gauge , BRAWA in October 2012