Frequently Asked Questions: General

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Application Notes CV Calculators Documentation FAQ: General DAC10 DTM16 DTM30 SIGM10 SIGM20 LocoAnalyse Ribbon Cables	How should I mount my boards? Many DCC and LocoNet interface devices are sold as open circuit boards, to be installed into a layout by the user. While this enables the user to put together a reliable layout with minimum fuss, these products can be intolerant of stray wires being dropped onto them or being powered up while on a conductive surface (including the black bags the products are supplied in). Few products will survive a live DCC track wire being dropped onto them. Consider mounting the boards behind a wooden panel or in a plastic sandwich box to keep stray wires out. How should I wire up my LocoNet? LocoNet has proved itself to be robust and capable of controlling very large layouts. Installations with hundreds of yards of cable and over 100 interface boards & throttles are possible with LocoNet. There is a lot of general advice available about optimum LocoNet cabling available on the internet. Start with Digitrax's own advice: www.digitrax.com/lnwire.htm Is my LocoNet cable working properly? Most reported problems turn out to be electrical problems with problems being caused by inadvertent wiring errors. One issue that has caused problems on several layouts has been poorly crimped connectors on LocoNet cables. In several instances this has resulted in a connection that has high resistance, but isn't open circuit. The result is that the cable tests OK with an LT1 but doesn't work properly in practice. This can be tested for by using a multimeter to look at the voltages on the cable. On a "healthy" LocoNet, the voltage measures from DCS100 "ground" terminal to the centre two LocoNet pins should be 10v or more. However if a cable has a high resistance connector, then the voltage down that segment of LocoNet can be dragged down. Voltages as low as 4v have been seen due to this. If you suspect your LocoNet is not working correctly, check the voltages to the centre two pins and investigate if is less that approx. 9-10v. The outer pair of wires provide "rail sync" signals with the same packets as are present on the rails. These can sometimes become open circuit, often without afecting many devices they're connected to. I'm not familiar with ribbon cables Ribbon cables are a convenient way to connect from boards such as accessory decoders to switches and LEDs. They offer a low cost, connectorised way to terminate a lot of wires to a board reliably. A ribbon cable typically consists of 10 or more wires whose insulation joins them together side by side. They can be cut with scissors, sharp knives or tin snips and joined or extended with readily available connectors. The individual wires in ribbon cables are conventionally numbered consecutively with wire 1 having the red stripe on the cable. This connects to the board's connector pin 1, which is commonly marked with an arrow. Ribbon cable connectors can be assembled readily with conventional tools. The simplest way to crimp a connector onto a ribbon cable is using a bench vice. Assemble the two connector halves onto the wire and check visually that the cable "tines" (the "vee" shaped pieces of metal that will pierce the insulation) are aligned with the strands of wire. Then carefully put the two connector halves between the jaws of a vice and squeeze slowly until the two halves click together. To wire to the other end of the ribbon cable, simply peel the wires apart (a scalpel or other sharp knife may help) and strip the insulation from the end carefully. Solder the bared ends to the switch or LED (or whatever) and make some provision for strain relief: the bare wires will not tolerate much flexing. How should I provide power to my boards? In general, different kinds of boards need different power supplies. This is because there are no standards for power feeds in the DCC world, and every manufacturer has (potentially) different power feed arrangements. These power feeds al need to be isolated from each other: i.e. they need to come from separate transformer windings that are not commoned together (e.g. by a common earth). Some general rules follow. No DCC or LocoNet accessory product should be connected to the same transformer winding that goes to a booster (e.g. DB150 or DCS100). DAC10 and DS54 accessory decoders can share a common power feed provided that the power feed is wired the same way to each board i.e. all the board grounds end up connected together. The power feed to these devices should not go to any other DCC or LocoNet interface unit. DTM16 (revision B onwards) and SIGM10 boards can share power feeds: they have the same power supply design. It may be possible to share a power feed between DTM16/SIGM10 boards and BDL162 boards. There has been a problem with such a configuration but it was believed to be due to a defective component. However this cannot be guaranteed to be possible and a separate power feed would be preferred. It may be possible to share a power feed between DTM16/SIGM10 boards and a locobuffer. Which is the Anode on my LEDs? The documentation for CML Electronics' products will refer to "anode" and "cathode". When an LED is lit, the positive end is called the "anode" and the negative end is called the "cathode". To add to any confusion, by convention the cathode is often marked with a "plus" symbol. If you look into the body of an LED, you will see an "anvil" like structure attached to one pin. This will be the cathode. The other pin is the anode. The cathode is often marked with a "flat" on the package, and the anode's lead is sometimes longer.   What addresses should I set for my boards? A perennial problem is the issue of choosing accessory numbers for boards to deconflict them from each other. Some of the number ranges overlap; others do not. the following guidance is offered. Many accessory boards have a "DCC accessory address". This is an address that is accessible through DCC "closed" and thrown" commands from a throttle. Examples are all point control accessory decoders; SE8c signal controllers; and SIGM10 signal controllers. DCC addresses can be between 1 and 2048 (although many throttles can't control addresses above 999). It is important that the addresses allocated for these board do not overlap with each other. A DS54 accessory decoder will occupy 4 DCC accessory addresses. The number of the first address (its base address) is programmed by values in CV1&CV9. The board occupies addresses between "base address" & "base address + 3". A DAC10 accessory decoder will occupy 8 DCC accessory addresses. The number of the first address is programmed by values in CV1&CV9. The board occupies addresses between "base address" & "base address + 7". An SE8c signal controller will occupy 64 consecutive addresses. A SIGM10 signal controller occupies 16 consecuive addresses. It is also possible to program the board to respond to some other accessory addresses to do specialised things. It is a good idea to document carefully what decoders are used for which purposes, and what addresses are assigned to them. If a board is inadvertently assigned to an address overlapping another board, no damage will result but the user will find that setting one address to CLOSED may cause response in more than one decoder board. Some board occupy "sensor addresses". As a general principle, there are two sensor addresses for each DCC accessory address: therefore there are a total of 4096 sensor numbers. Early interface boards (e.g. DS54) use the same address programming to control both the sensor address and the DCC address. If the DCC addresses didn't overlap, then the sensors will be automatically deconflicted too. Other products (e.g. BDL16, BDL168) program the sensor address using a "board number, sensor number" approach. The overlap between these two numbering schemes causes greatest confusion. For example: A DS54 board will have 8 consecutive sensor addresses, beginning at "2*base address -1". A DAC10 board occupies 16 sensor addresses (although only 10 are used) beginning at "2*base address -1" A BDL16 or BDL168 occupies 16 sensor addresses, with a starting point defined by the initial board configuration entered through a throttle. Broadly speaking the user enters a "board number" with the throttle, and each board number occupies 16 sensors addresses. To convert to a sensor number, the first sensor position occupied is "16 * board number - 15" A SIGM10 can be programmed to occupy 8 sensor addresses, using an assigned board number.  The first sensor position occupied is "16 * board number - 15" When this is daunting, the safest approach is to experiment. Use a loconet message viewer on a PC to see the messages generated by the various boards & sensors. In general no 2 boards should generate messages with the same numbers. If it turns out there is an overlap, reprogram one of the boards.
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