HANDY ACCESSORIES
for
DCC LAYOUTS

This section contains DIY circuits which can make operating your DCC layout even more enjoyable. Finding the parts is easy...they're mostly available from your neighborhood Radio Shack and others -- except possibly for the DCC uncoupler (RS part nos. are in parentheses after each component). I hope that you'll try several of them.

  1. Accessory Switch  
  2. Power Supply for Digitrax PR-1  
  3. Occupancy Detectors  
   4. Uncoupler (HO)  
  5. True-RMS Ammeter  
   6. DCC-BitSwitch  

If you have any problems (or would like to try some modifications), just Email Me (Fred Horne), and I'll try to help.

ALL THE ABOVE CIRCUITS (or links to 'em) are on this page...just scroll down.


1. Accessory Switch

This delightfully simple project allows you to control all the lighting, turnout or signalling power supplies, animation and other accessories on your layout without having to throw a plethora of toggle switches. Whenever you apply (or remove) track power, AC power will automatically be applied to (or removed from) your various accessories. This one's very simple...and very handy. The parts shouldn't cost you more than $10-12.

A Short Writeup on the Project
The Schematic Diagram
An Assembly Drawing


2. Power Supply for the Digitrax PR-1 Programmer

The PR-1 is a handy little thing, but many folks seem to have problems due to inadequate power supplies. The PR-1 demands a very pure DC supply (ie, ripple less than 5mV) which is hard to come by from a "wall-wart" supply; adding a 2200uf capacitor clearly helps, but sometimes still isn't good enough.

In my experience, the problem is sometimes compounded by a cranky PR-1 that demands higher than specified voltage to program reliably. My personal PR-1 is quite erratic until the DC supply reaches 20 volts -- then it goes right to work! Don't worry about frying your PR-1 by putting higher voltage to it -- the Digitrax gurus tell me that anything below 22 volts is OK (just make sure that the regulator is reliable and the meter you're measuring with is accurate).

I created this circuit to power my PR-1, and even added a switch to select between "LO" voltage output (about 17.5 volts) and "HI" voltage output (20 volts); choose the setting that works best for your particular PR-1 (and don't substitute resistor values for R2 and R3 unless you are sure you know what you're doing). I housed mine in an RS plastic "project box" -- with plenty of ventilation holes so the heat sink can get air. Total parts cost should be in the range of $15-20.

PR-1 HINT -- In some PCs, the UART IC which provides the serial ports (COM ports) isn't particularly fond of the PR-1 interface, and programming becomes erratic for reasons other than the power supply. If you've provided well-filtered, 20 volt DC to your programmer and are still having problems, try changing the "baud rate" from the PR-1 window. Some users even have to change "buffer sizes." If none of this works, you may have a sick PR-1; contact Digitrax -- they're very good about helping with such maladies.

Schematic Diagram
Other Output Voltages



3. Occupancy Detectors

Here are three approaches to Occupancy Detection. The first is my Simple Optical Occupancy Detector (SOOD); it works with both DC and DCC systems in all scales, but does require that you have some illumination on the layout (if you like to operate in the darkness, this one's not for you). It's great for staging yards (hidden and otherwise) where you'd like to know length and position as well as simple presence; since the cost is quite low per unit, you can put them every 3" if you need such resolution.

There are also links to two very good non-optical designs: first, Don Crano's circuit which is opto-isolated at the input allowing the use of a common power supply for all detectors on the layout; second, Dick Bronson's circuit which is opto-isolated at the output and includes a regulated power supply for each detector. Both are solid designs.

SOOD Description & Schematic
Don Crano's Detector
Dick Bronson's Detector


IF you're not inclined to Do-It-Yourself electronic projects (or if you just like 'em built 'n' tested), there's the Digitrax BD-1 detector which was designed for use with their own DS-54 Stationary Decoder.


4. Uncoupler (HO)

Located on another web site. Just CLICK HERE to take a look.


5. True-RMS Ammeter

Since DCC is a "variable-duty-cycle, non-sinusoidal" signal, any attempt to read voltage or current using conventional panel meters or low-cost multimeters will produce only incorrect and frustrating readings. Accurate readings require "True-RMS" meters. While the track voltage is not a very interesting value (it's set by the booster, closely regulated, and never varies), the current drawn by the DCC layout can be useful information. The circuit shown below converts a conventional DC panel meter into an accurate "true-RMS" ammeter.

This circuit is the original work of North Coast Engineering.

I've modified the circuit to use a more-available NPN transistor. This is not your garden- variety junk box NPN, however; it has an emitter-to-base breakdown voltage (BVebo) of greater than 15 volts (most NPNs are in the 5-7 range, and won't do the job). The NTE2505 device shown is a "universal replacement" type of critter, and available by special order thru Mouser (800-346-6873, ) or Allied Electronics (800-433-5700). The circuit is simple and well-tested. All the passive components are widely available (Radio Shack, Jameco, etc.), but the meter may take a bit more searching -- a 0-1 DC voltmeter will do nicely, as will a 0-50 DC microammeter with a 10 Kohm series resistor. A digital panel meter could also be used (very classy!); just ensure that the meter module has an input resistance of at least 100 Kohms. You could also use your handy multimeter on a low-DC volts range for occasional measurements.




NOTE:
If you're not the DIY type, take a look at the DCC Ammeter circuit that
Tony's Train Xchange
offers ready-to-run. It looks good to me.



6. DCC-BitSwitch™

The DCC-BitSwitch alters the bit packets sent to any section of track and activates the braking or acceleration momentum for any locomotive occupying the controlled section. This provides smooth, individually controlled, start and stop operation for any number of trains on your layout. These switches will allow several variations in automatic dispatching sequences for DCC layouts where the operator does not wish to invest the time or incur the expense required for automatic operation using personal computers with their related software, occupancy detectors,etc.

The design of this switch allows the engineer to choose totally automatic operation, conventional DCC only, or any combination of both. These modes can be changed for separate sections with either a DCC CAB command (optional) or a manual control switch that is toggled between conventional and automatic modes for each area of your layout.

Complete info located on another web site. Just CLICK HERE to take a look.




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Updated 11-14-04