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Last updated: 26th April 2012

MERG, CBUS and DCC (624 kbytes)
A paper presented by Ian Both at the Modelling of the Railways of Queensland Convention 2012

DCC now fully integrated on CBUS

CBUS-DCC System Operating Instructions.

This is a summary, the full instructions can be downloaded as a pdf if required.


The CBUS DCC system comprises

  1. A command station (CS) with integral mini-booster / programmer.
  2. CABs (or handsets)
  3. DCC Booster or boosters for larger layouts

Power supply.

The CS requires an AC supply of 15V (12 to 16 V) or a DC supply of 15 to 24 V. The current should be at least 2 amps. When power is applied to the CS, the green LED should be lit. The CABs require a 5V supply which may be taken from the CS or supplied separately.

DCC boosters.

The CS has an output for conventional DCC boosters (eg. the MERG NB1). This is a 5 to 15 V DCC signal which will suit most boosters. The CS also has a low power output stage which may be used as a mini-booster. This is set at 1 amp maximum and the DCC voltage is again adjustable. It is not possible to use this output stage as a mini-booster and a ‘service mode’ programmer at the same time. The mini-booster output is short circuit protected. This does not affect the separate DCC booster output.

Adjusting the output voltage.

The CS has a small ‘trimpot’ for setting the output voltage labelled VR1. This voltage is common to the mini-booster and DCC outputs. Apply power to the CS. Attach a voltmeter between the 0 (-) and + outputs of J5. Turn VR1 till the voltage is the desired value. For use as a booster, set to 12 to 14V. If driving a separate booster, 12V is recommended.

Attaching a booster.

The CS supplies a DCC signal which a positive waveform from 0V to V+, where V+ is the voltage set by VR1. Connect the external booster between the 0 and D terminals of J5. A suitable booster is the MERG NB1A or NB1B.

CAB wiring.

The CABs connect to the CBUS using 4 way RJ22 connectors. Connect the CS to the CBUS in the usual manner. J2 is a CBUS terminal block. A 5V supply (1 amp) is available on this TB but if the CBUS has a separate 5V supply, this should not be connected. If the CS is to be attached only to CABs, there must be a terminating resistor (68 ohms) across the CANH and CANL wires. This may be fitted at J2. The CABs are connected to the CBUS via a small adapter PCBs fitted with a RJ22 socket. The bus wires may be soldered directly to this PCB or it may be fitted with a CBUS style terminal block (3.5mm spacing). Use of a TB allows easy ‘daisychaining’.

The CABs plug into the sockets using a standard ‘telephone handset’ cable – the sort used to connect telephone handsets to their bases, not the type that connects to the BT wall socket. Note: These cables are not a ‘one to one’ connection but are a ‘mirror image’ at each end. The wiring in the CABs allows for this. Do not use any other type of connection or the CABs may be damaged.

Mike Bolton and Gil Fuchs © November 2007

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