MS sound decoders for small scales (N to H0)

The dimensions of decoders with standardized interfaces (PluX, MTC, NEM-651, Next18) correspond to the corresponding standards by VHDM and NMRA or are smaller. In case of the wired decoders, which are protected by a shrinking tube, the indicated dimensions are WITHOUT this tube, because it can be taken off, if there is not enough space.

The indicated number of stranded wires for the miniature decoders refers to the free wires of the fully wired variants. -R and -F variants have NEM-652 and NEM651 connectors respectively, which accommodate part of the wires; just as -L and N variants only have connections as wires that are not on the directly soldered-on connectors.

MS491R and MS500R: 8 wires at the connector (2x motor, 2x track, front light (F0f), rear light (F0r), FO1, common positive pole) and 4 free wires (FO2, ground, 2x speaker). MS491F u. MS500F: 6 wires at connector (2x motor, 2x track, light front (F0f), light rear (F0r)) and 6 free wires (FO1, FO2, ground, 2x speaker, common positive pole) MS491L, -N u. MS500N: 6 pins (2x motor, 2x track, light front (F0f), light rear (F0r) and 4 free wires (ground, common positive pole, 2x speaker)

“Total current” means motor current plus current of the function outputs plus consumption of the sound generators. Usually, the current used by the consumers on the function outputs is very low (only a few LEDs), as is the current consumption for the sound production (as average over time) also, so that the “total current” usually is available for the motor output. Therefore, the “total current” and the “motor current” are usually indicated with the same value. In case a function output has a higher continuous load (e.g. because it has a smoke generator connected) the motor output provides less current.

NOTE: The continuous load is – against common interpretation – not limited by the motor amplifier, but by the heat development on the PCB. Therefore: the smaller the decoder – the less current flows, especially less total current.

Continuous Current

The continuous current indicates the possible continuous load at normal conditions (normal room climate and circulating air in the room where it is used). At about 100°C (212 F) on the PCB, the temperature sensor shuts down the consumers (in contrast to exceeding the peak current, at which the current sensor reacts).

At overload or overtemperature, the headlights start flashing at fast pace (about 5 Hz = 5 times per second). As soon as the PCB cooled down for 20°C (hysteresis), the motor is turned on again automatically.

The actual resilience of the motor is influenced by various factors, e.g. the track voltage (the higher, the more heat loss and the lower the possible continuous current), type and condition of the motor (low-ohm, etc. ) Dirt and heat from the outside are not helpful either.

ZIMO decoders can be overloaded (50% - 100% up to the “peak current”) for a short period of time. Usually, the peak current can be endured about 20-30 seconds, but only if the decoder was not at its limits beforehand. Currents in the medium area are naturally fine for a longer time, usually for a few minutes. This way, the usual hills on a model railway layout can be overcome, on the way down the hill the decoder cools down again.

Peak Current

While the “continuous current” refers to a long-time heat development of the decoder, the “peak current” indicates the threshold on which the current consumption (even with hypothetically perfect cooling) reaches the maximum of resilience of the motor amplifier. After reaching this threshold, it takes a few seconds or milliseconds until the decoder is shut down permanently. The fastest possible shut-down is reaching the threshold via a short circuit (depending on the type of decoder between 4 A and 10 A). ZIMO decoders possess an intelligent system, which prevents unnecessary shut-down but still is secure.

In case of a motor shut-down due to exceeding the peak current or because of a short circuit, the decoder is switched on again after about 3 seconds, but in this state it does not show any signs, like when shutting-down because of over temperature.

The output current on a function output is indicated as sum (of all FOs or groups). A single output is, nevertheless, strong enough to handle the total current alone.

In case of an overcurrent, the decoder is turned off immediately, but depending on the anount exceeding the limit within a few tenths of seconds or milliseconds. This makes the cold start of light bulbs possible (if this is not enough, this can be defined within the software as “Soft Start”).

There are different kinds of (function) outputs:

• “normal” function outputs”, often also called “amplified outputs”, to which front lights, light bulbs, uncouplers, smoke generators etc. can be connected. Each of these “open-collector outputs” is connected to the negative pole of the consumer; the positive pole of the consumer is connected to:
  • Either the “common positive pole” of the decoder (on wires: the blue one)
  • Or to a low-voltage output of the decoder if it has one,
  • Or to an external power supply (e.g. a voltage regulator which is directly supplied by the tracks)
  • Or (if there is no positive pole accessible, often at miniature decoders with NEM-651 interface) to one of the track poles (has the effect of reduced brightness of lights)
• “Logic-level outputs” (“unamplified”) are outputs, which supply a voltage level (5 V / 0 V) depending on if they are switched on or off. They are supplied via an internal protective resistor (usually 10 kOhm, i.e, a maximum of 0.5 mA current). Those outputs can be used:
  • Either with the help of an external amplifier, either self-made or with the ZIMO product M4000Z
  • Or as servo control wires (the traditional servos are compatible with the logic-level outputs)
  • Or as control wires for SUSI interfaces, and for I²C busses.
  The typical two logic level outputs, which almost every ZIMO decoder has, are switched between the possible applications by CVs.
  By factory default these "SUSI pins" are set as SUSI Clock u. Data as follows: Logic Level CV #124 bit 7=0, Reed CV #393 bit 5=0, I²C CV #394 bit 2=0, and Servo Control Line CV = 0 (CV # see line 'Servo control wires").
  If you want to switch to logic level outputs, set CV #124 bit 7 = 1 (value 128). The function of the outputs is now defined and the CV values of the other possible modes listed above are ignored. If the logic level is inactive (bit 7 = 0), the next active value of the function modes in this order is valid.

Decoders with 21MTC interface do have function outputs which are either logic-level or amplified:

The decoders MS440 are available as “C” or “D” types. The variations “C” and “D” differ (like all ZIMO MTC decoders) in the type of FO3 and FO4, at current decoders (like MS440 or the “old” MX636) also FO5 and FO6.

“C” (the “standard” type): FO3, FO4, FO5 and FO6 are logic-level outputs, i.e. only usable with an external amplifier (e.g. loco board)
“D” (the ZIMO type): FO3, FO4, FO5 and FO6 are “normal“ function outputs and can be used directly by a consumer. In this version the standard switching input IN2 on Pin2 is replaced by a logic level output (switchable via CV #393).

If the logic level outputs/SUSI pins are switched to servo control wires by means of CVs (see above, line "Number and type of function outputs"), commercially available servos (Graupner, Robbe, etc.) can be controlled, for which various operating modes, end positions and rotation times can be set.
A setting (CV value > 0) activates the function as servo control line (if logic level, reed and I²C are deactivated, see above).
Responsible CVs for most MS decoders are CVs #181, #182
(not with large scale decoders:
for MS950 #183, #184,
for MS990 page 145 #281, #282).

The 5 V supply for the servos has to be provided externally, as far as the decoder does not have a low-voltage output.

By default, the SUSI signal (SUSI Data, SUSI Clock) is present at the logic level outputs (see line "Function Outputs") because bit 7 of CV#124 is not set (binary 0). By setting bit 7 of CV#124 to binary 1, the SUSI signal present there is deactivated and you can use the two pins as switchable logic level outputs if CV#181, CV#182 = 0 at the same time, because otherwise a servo control signal is present at these two pins.

The SUSI interface is used in vehicles with – partly upgraded – interfaces for data transmission, where electronics are integrated, i.e. panto drives, smoke generators, uncouplers, etc. The original idea of the SUSI interface, namely controlling external sound modules, has moved to the background, because sound decoders provide better solutions and in contrast to the past can be manufactured with smaller dimensions.

The SUSI pins of the ZIMO sound decoders used to load sound projects fast and efficient (2 minutes instead of 10 via tracks) has nothing to do with the original protocol and thus does not haveto be configured. Switching to this operating mode is done automatically before starting to load the sound project via the sound loading device MXULFA or a correspondingly developed ZIMO command station.

Switch inputs are used to connect cam sensors directly (to play back chuff sounds synchronously to the axles) or sensors for position dependent sound functions, e.g. warning whistles before a level crossing.

Note: The logic-level outputs (see above) can also be used as switch inputs, if needed and the software supports functions with switch inputs (e.g. position dependent lighting effects or loco controlled commuting. This is also valid for non-sound decoders.

** For decoders of the MS480 family only valid from revision B, produced from approx. August 2022.

Most MS-Sound decoders have a 5 V low-voltage source, which serves e.g. the operation of LEDs. This means that less energy is "burned up" than if the LEDs were operated at full voltage via a 1.5 kΩresistor, for example, and also that fluctuations in the track voltage are kept away from the lighting, i.e. the brightness fluctuations are avoided.

The power of the current available on own solder pads is normally max 50 mA. This is sufficient for LED lighting - but servos cannot be operated with it!
The MS440 and MS450 decoders (all types) as well as the MS581N18 still offer 200 mA, this is also sufficient for operating small servos or lights. MS440C/D have the 5 V source, according to the standard, at the MTC connector. With the MS450 , the 5 V can be taken off at a soldering point on the bottom, as shown on the connection diagram. However, this is only recommended for experienced solderers! The MS581N18, however, offers a normal soldering pad for soldering.
Connection diagrams can be found above in the info section   of the respective decoder and also in the instruction manual.

A stay-alive capacitor connected to the decoder in the form of Elkos (electrolytic capacitors), Tantals (Tantal capacitors) or Supercaps (old denomination: Goldcaps) takes over the supply of the decoder and connected consumers during interruptions of the wheel-track-connection due to dirt, insulated frogs or similar. Starting with a capacity of about 200 µF a positive effect can be seen; at least 1000 µF are recommended.

Additionally to preventing getting stuck, flickering lights and interruptions of the sound, a capacitor also reduces heating up the decoder (by reducing blind consumption) as well as motor sounds (limited by bridging the supply gaps by RailCom or HLU).

ZIMO decoders (except miniature decoders) contain a circuit for a direct energy-storage connection – of Elkos, Tantals or Supercaps – i.e. without additional components. This circuit provides an ideal (limited by standard current) charging and discharging of the capacitor and is included in the decoder price, in contrast to power-packs and other auxiliaries, which are needed for non-ZIMO decoders. Furthermore, for connencted Elkos and Supercaps it is enough to have resilience until 15 V, even if the running voltage is higher (Tantals should have a voltage reserve due to their type of construction, i.e. a minimum of 20 V). MS decoders (in contrast to MX decoders) do NOT have a limit concerning capacitiy; more than 1 F is nevertheless not very practical.

The decoders MS480, MS491 and MS500 have a simple charge and discharge circuit, which is why only an energy storage device with low capacity can be connected to them (max 1000µF). For the energy storage connection Elkos and Tantals with a resilience of at least 16V are sufficient, even if the driving voltage is higher.

The MS581 has a charge and discharge circuit for capacitors with a resilience of at least 5 V, to which, among other things, 6.3V Tantals can be connected.

With each sound decoder, a speaker with 8 Ohm can be used; a wide range is available from ZIMO.For MS decoders with 3 W audio, 4 Ohm speakers are also suitable, or 2 to 3 8 Ohm speakers that can be connected in parallel.

ZIMO recommends the rectangular miniature speakers with an integrated resonance body, also called “Sugar cubes” (LS10x15, LS8x12) which are especially efficient (i.e. high volume with little space requirements).

Nevertheless, the saying “the bigger the better” is still valid. Of course, the sound quality also depends on proper installation (resonance body or hermetically sealed loco housing as resonance bodies, openings in the housing, etc.)

To the speaker outputs of the large-scale decoders, either 4 Ohm or 8 Ohm speakers can be connected. Those outputs supply 10 V of voltage (in contrast to HO and miniature decoders, which only supply 5 V), what makes a performance of up to 10 W on 4 Ohm possible. Furthermore, large-scale decoders are equipped with 2 independent speaker outputs, what can be used by especially designed sound projects, to let the bell sound from another location within the train, or also to acoustically separate the two motors of the train.

MS decoders possess a sound flash of 128 Mbit and possible frequencies of 22 and 44 kHz. (22 kHz are standard, what provides playback time of 360 seconds (with 16 bits).