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