The Signaling Solution, Inc.
PO Box 25
West Terre Haute,
IN 47885
Phone:(812) 533-1345
Fax:(708) 570-6140

BD16 Block Occupancy Detector: All Scales

by David Frost
Reprinted by permission of RAILROAD MODEL CRAFTSMAN
March, 1996


W.S. Ataras Engineering has entered the hobby with the BD16 Block Occupancy Detector, a detection device that can handle 16 track segments (blocks) at a time and provide a variety of outputs for control panel lights, signals or accessory activation. It is suitable for use on layouts with either conventional d.c. control systems or those employing command control.

The Ataras BD16 detects a train from the presence of a current flow through the rails. As such, it is suitable for all scales on a.c. electricity. Track current is led through a diode matrix, rated at 3 amps, that produces a voltage drop of 0.7 volts, but this will not be obtrusive under normal circumstances.

The detector produces two outputs for each block and these can be handled in several ways depending upon the signaling and control system. The simplest possibility is to have two light-emitting diodes (LED's), red to indicate that the block is occupied and green when the block is vacant. The BD16 provides a source of 5 volt d.c. power and appropriate resistors to reduce the current for normal LED's. The resistors are contained in four tan-colored micro chips which can be removed if another resistance is required. Then, 0 ohm "modules" are substituted for the resistors. Modelers must supply the appropriate resistors beyond the BD16.

The BD16 is a 6"x7", double-sided printed circuit board or card with all the components neatly soldered to one side. The card plugs into a connector which has 80 separate terminals, 40 on each side. There is also a separate 6-volt power transformer for the board which plugs into a socket in the lower left-hand corner. All other inputs to and outputs from the detector pass through the connector.

I strongly suggest soldering labeled wires to all the terminals of the connector before you install it somewhere beneath your layout. Identifying the correct terminals and soldering 60 to 70 clean connections is terribly difficult in gloomy and constricted spaces as I found out the hard way.

A 50-page book accompanies the detector. Lest this seem needlessly intimidating, most of it is a general discussion of different model railroad control systems and an analysis of methods of train detection. Everyone should read these parts of the manual, as they will serve to refresh the memory of even the most expert model electrician and make sure that the rest of us know what it's all about. Other sections of the manual deal with configuring and installing the detector and connecting the outputs.

When we wire up our layouts, we usually join together one output from each power pack to form a common feed to one rail. We then pass the second outputs from the power packs through toggle or rotary switches which allow us to select which power pack will control the train in which block. This is usually called "common rail" wiring. With this system, the ground of the BD16 is attached to the common wire from all controllers. Then a wire must be run from the common rail of each track block to a specified terminal on the BD16's connector.

On my own layout, I have a heavy common wire running to all major areas, and the common rail of each block is connected to this heavy wire. I had to cut these connections to the heavy wire and instead run a wire from each common rail back to the BD16. Think for a while about the best place to install the detector so you minimize any new wiring of this kind.

The BD16 gains its versatility by asking you to make a couple of configuration setting before installation in much the same manner as manufacturers of PC modems. A two-pin jumper defines whether or not you are using command control, and two other jumpers define which of your rails is common. If like me, you do not conceive of your common rail as North, South, East and West, leave off the jumper and forget about it.

The BD16 has two outputs for each block, one which is energized when a train is present, while the other energizes when the block is vacant. These outputs are designed for LED's which are connected to these terminals and the 5-volt terminal on the connector. Red and green LED's can then be wired into a control panel or installed in a two light signal.

The detector has been well thought out with a suitable delay incorporated into the detection circuit. Thus, there is a second or two delay before the red LED switches to green and dirty wheels or track do not cause the signals to oscillate back and forth between indications.

If you wish the detector to report to a TTL signal control system, the original resistor IC's should be retained and the appropriate output connected to your TTL circuitry. If you wish to switch heavier loads such as relays for crossing gates, you must use the 0 ohm IC's and provide another power supply. Unfortunately, you cannot decide to have, say, three outputs drive relays and the rest switch LED's. At best, you could decide to have eight blocks work LED's and use the other eight blocks for relays. Check the board very carefully to see which pair of IC's you need to change for 0 ohm resistors.

I have wired the test sample into my ten-year old layout, and I am using the outputs to drive control panel lights in some cases and as input to TTL signaling in others. The detector is working perfectly, and I am very pleased with the results.

The BD16 has a suggested retail price of $250.00, which comes to around $16.00 a block. This is quite competitive with purchasing individual detectors and wiring them separately. I like obtaining 16 block detectors at once. This is the motivation I need to complete signaling the next major portion of my layout. If you do not need 16 blocks, I believe that Ataras Engineering is developing an eight block unit. Should you need greater than three-amp diodes, check out the BD16HC which is intended for O scale and garden railroads.

In short, the BD16 Block Occupancy Detector is sophisticated, well thought out, well made and supplied with an excellent instruction book. Ataras has just announced a four-block, three-aspect signal controller, the TC4 ($70.00), and they are willing to sell their instruction manuals separately for $7.00, refundable with an order. These fine products should be ordered directly from W.S. Ataras Engineering.


Product Update:
The BD16 User's Manual is now available for free download from the website and a printed manual is available for seperate purchase.
Our current address and contact infomation is given below
The Signaling Solution, Inc.
PO Box 25
West Terre Haute, IN 47885.
Phone: (812) 533-1345
Fax: (708) 570-6140
The Signaling Solution, Inc., PO Box 25, West Terre Haute, IN 47885. E-mail: