Frequently Asked Questions:

DTM16

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FAQ:
General
DAC10
DTM16
DTM30
SIGM10
SIGM20
LocoAnalyse

Ribbon Cables

 

How do I connect pushbuttons & LEDs?

To connect the pushbuttons, split the ribbon cables that will go to SK3 & SK4 into pairs of wires. Then simply connect a "push to make" switch onto the end of each pair.

To connect the LEDs, you will need to wire to the 5 pin plugs that go to connectors PL1-PL10.

To connect two cells to control points, wire as follows:

To wire the first cell to control a point and the second cell to display two sensors, wire as follows:

What sort of wire should I use for the LEDs?

Any cable will do: the current carried is around 5mA per LED. Thin multistrand wire is best, with a pliable insulation (e.g. PVC). I have used 7/0.2mm equipment wire & ribbon cable. The key issue is avoiding mechanical strain on the connector pins, that may be fragile. I would recommend some kind of strain relief near to the board (e.g. a cable clip). If you cut the visible pins down to a length of 2-3mm, you will be able to solder to them but they won't be able to bend over and touch the adjacent pins.

What sort of LEDs should I use?

There are no restrictions. The board limits the forward current through the LEDs to approx 6mA. However, to achieve a bright display panel, it would be appropriate to try to get "high brightness" LEDs. These provide a lot more light for a given current than older LEDs. The simple solution is to try it & see. Consider allocating a colour scheme for LEDs if you are displaying several functions on the panel.

If you want to drive multiple LEDs for each output state - e.g. to light up a track path - then LEDs can be connected in parallel. However, brightness will begin to fall. Again, try it & see. It has been found that blue LEDs have much higher brightness than red or green, and one layout has panels with several parallel blue LEDs still giving a very intense light output.

What does the green LED tell me?

The green LED provides useful diagnostic information to help get  DTM16 up & running. The green LED is lit for approx 10ms every time a correct DCC packet is decoded. Since packets should be received every few ms, it should stay lit. (With DC stretching the LED may flicker slightly).

If the green LED is lit, the DTM16 is seeing the DCC signal correctly; if it is unlit, it is not seeing a DCC signal and the wiring should be checked.

When a DCC command is sent to the board (i.e. to change a point on the board to closed or thrown) the LED will flash off twice in quick succession. This provides an indication that the board address has been correctly set.

How does the DTM16 know the point states?

The DTM16 does not memorise point states when power is removed: it determines them during each operating session. Consequently, after power up, all the LEDs are off because the DTM16 does not "know" the correct states. It is able to determine the point states after power is turned on by decoding both the DCC rail messages and the LocoNet messages. It will find out the states by the following methods.

  • Digitrax command stations invoke an "interrogation" sequence after power up. Accessory decoders that are connected to LocoNet (e.g. DS54, DAC10) will report the states their points are at using both "output state" and (if position feedback switches are wired) "turnout feedback" messages. These messages will notify the DTM16 of the initial states. BUT note that the DS54 will not report the correct states for solenoid type point motors without feedback switches being wired up.

  • If a point is changed by a throttle, the DCC command to the point will be detected and the DTM16 will know the correct state.

  • If a point is operated by the DTM16, it will request the point go to a state and the state will be known.

  • The DTM16 does have an "initialise" feature: by using one pushbutton, all connected points can be driven to a known state. For a layout without DAC10 or without wired position feedback, this may be the simplest option to get up and running.

When I push a button, Nothing Happens

If nothing at all happens (e.g. no LEDs become lit or change state) there may be a problem in the wiring of the pushbutton switches.

  • Check that the switch contact is closing correctly when pressed: use a multimeter to buzz out the cable to the ribbon cable header.

  • Check that no other pushbuttons are stuck down: the board will not respond if there appear to be more than 1 pushbuttons pressed.

  • Check there is no wiring "short" that has the effect of making two switches appear to be pressed.

When I push a button, I get both cell LEDs stay on.

When a pushbutton is pressed, the software sets both LEDs on to indicate that the point is in an "unknown" state. When it gets a message response, it lights one or other LEDs to display the new correct state. If both LEDs stay on, it means that it didn't get that message response. Consequently there must be a problem in one of the following areas:

  • The DTM16 sending a message to the command station (e.g. DCS100);

  • The DTM16 seeing the DCC track signal;

  • The DTM16 seeing LocoNet messages.

Several things have been found to cause difficulty. Check all of the following:

  • Is the LocoNet cable plugged into front of UP3 or similar utility panel? The front connectors are suitable only for throttles because the rail_sync signals (a version of the DCC track signal) is not passed out to the front connectors. The LocoNet cable must always be connected to the rear telephone connectors.

  • Are the LocoNet cables OK? We are aware of several instances where a LocoNet cable that passes a test with an LT1 tester is actually high resistance, affecting the messaging.

  • Are the two jumpers (JP1, JP2) on the board removed? These should be REMOVED for normal operation, and only inserted for programming on a programming track.

  • Is the board correctly powered? DTM16 boards should not share a transformer winding with the boosters, or with power fed to some other types of device e.g. DS54 or DAC10. This can lead to "ground loops" with short circuits introduced via the return path. There is more advice in the general FAQ.

  • Is the board's green LED lit? If not, this suggests a problem with LocoNet cabling, or the track power is currently switched off.

 

 

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