Interlocking In A Box 
User Manual¶
Overview¶
The Iowa Scaled Engineering Interlocking In A Box is a simple solution for adding automatic or manual interlocking signals where one track crosses another at grade (a diamond). Stand-alone automatic interlockings were common, particularly on granger roads in the midwestern US where competing branchlines criss-crossed running to every little dot on the map. Some of the larger ones had towers and operators controlling them, but many were simpler operations that involved automatic signals where the first train to approach - or the first crew to unlock the cabinet and push the button in manual cases - would get a signal to cross. The Interlocking In A Box helps add this sort of operational interest to your layout - a way to slow down your operators from just barreling across that diamond without a care in the world.
This version concentrates on the core use case - a simple, single track crossing where one track is an operational part of the layout and the crossing track is not - and the goal is to force your crews to slow down, wait to get the light, and then proceed. It's designed to be easy to install and configure - the detectors just plug in, configuration of delays is done by switches on the board, and signals just connect into the terminal blocks.
When set up for an automatic interlocking, the Interlocking In A Box comes with three TrainSpotter optical detectors to sense the presence of a train on the approaches and in the diamond. Since these are optical detectors, no resistive wheelsets are required, simplifying the installation. To use it as a manual interlocking, the approach detectors can be replaced with pushbuttons or other momentary switches mounted on the fascia. In both cases, conflicting traffic on the diamond can be simulated through an adjustable, and randomized, delay. This delay causes an arriving train to wait some period of time before receiving a clear signal to cross the diamond, adding some variety to the operations.
Please Note
The Interlocking In A Box is meant for use with a single operational track that crosses modeled, but inoperable track(s), at a diamond crossing. For a crossing where both tracks are operational, or for use with double track, look for a future "Pro" version with more functionality.
Features¶
- Simulates an automatic or manual interlocking at a diamond
- Designed for simplicity and to cover most use cases
- Triggered by either TrainSpotter optical detectors (automatic interlocking) or pushbuttons (manual interlocking)
- Controls a 2-aspect signal capable of displaying stop and clear (typically red and green) in each direction on one track
- Optional delay time (fixed or randomized) between arrival and green signal
- Compatible with both common anode (positive) and common cathode (negative) signals
- Realistic signal fading during changes for both tri-light and searchlight style signals
- Simple plug-and-play compatibility with most Atlas HO and N scale signals
- 5V output for powering fixed aspect heads, such as red signals on the non-operational crossing track
- Includes control board and TrainSpotter optical detector(s)
- Powered from 6V to 24V DC, AC, or DCC power.
Typical Applications¶
- Adding signals to simple single track diamonds replicating automatic or manual interlockings
Quick Start Guide¶
Please Note
All wiring and setup of the board should be done with the power off. This significantly reduces the chances of accidentally slipping and causing a short circuit that damages the board, the block detectors, or the signals.
The two approaches to the diamond are called A and B, respectively. Both operate identically, but be sure to keep the A inputs with the A outputs and B inputs with B outputs when installing on the layout.
Step 1 - Signals¶
Common Anode vs Common Cathode
The Interlocking In A Box supports both common anode (positive) and common cathode (negative) signals, but all of the signals connected must be of one type or the other. Mixing common anode and common cathode signals on the same Interlocking In A Box is not supported.
Most applications will want to use two signals, one on each approach to the diamond. Three aspect signals can be used, but the Interlocking In A Box will only drive two of the LEDs. In most cases, this will be red and green.
LED signals with the usual red/green leads can be wired into the terminal blocks. The common wire should be connected to the COM terminal, and the individual color leads should be attached to the respective R (red) and G (green) positions on the Signal A and Signal B terminal blocks.
If you are using signals from Atlas, they will plug directly into the off-white connectors marked Signal A and Signal B. If the signal leads aren't long enough to reach the main board, Iowa Scaled Engineering offers extension cables.
Set the COMMON switch to ANODE / + if your signals are common anode / common positive (this is most common). Likewise, set the switch to CATHODE / - if your signals are common cathode / common negative.
The Interlocking In A Box powers the signals from 5 volts and has 330 ohm resistors on each of the signal outputs to protect the signal LEDs, so no additional resistors are needed externally. If your signals already have resistors built in, you will likely need to remove them or disable the onboard resistors. See the section below on Bypassing the LED Resistors.
To power signals permanently displaying a single aspect, such as distant signals, or dummy signals on the crossing track, you can use the 5V and GND terminals. You must use current limiting resistors in this case to prevent blowing up your signal LEDs!
Step 2 - Diamond Detector 
¶
The TrainSpotter provides optical detection. One TrainSpotter is always installed in, or very near, the diamond to detect when a train crosses the diamond. Use one of the included 8 foot cables to connect the TrainSpotter to the Diamond connector on the main board.
Step 3 - Approach Detectors¶
Automatic Interlocking¶
For a fully automatic interlocking, install the other two TrainSpotter detectors at the approaches to the diamond on either side. These should be sufficiently in front of each signal to trigger the Interlocking In A Box before the train reaches the signal. Use the included 8 foot cables to connect the TrainSpotter to the Block A and Block B connectors on the main board. Be sure the "A" detector is on the same side of the diamond as the "A" signal, and similarly for the "B" side.
Manual Interlocking¶
In the case of a manual interlocking, connect pushbuttons or other momentary switches (typically mounted on the fascia) to the Inputs terminal block. One pushbutton for the "A" approach connects between the A terminal and a GND terminal. The other pushbutton for the "B" approach connects between the B terminal and a GND terminal. Leave the D terminal empty. Do not use the 5V terminal for these switches.
Step 4 - Connect Power¶
Connect power to the board - it requires 6V to 24V of DC, AC, or DCC power. This power can come from a dedicated power supply, an accessory power bus, or from the track bus directly (but before any block detectors).
Step 5 - Initial Testing¶
Start with all the DIP switches set to OFF. You can adjust these settings later after verifying everything is hooked up correctly.
Apply power and check that the green power LED glows on the main board. This verifies that the Interlocking In A Box is getting good power. Immediately after power up, the signals will display both red and green in sequence. This is normal and verifies that the signals are connected correctly. The status LED on the main board will also flash through a sequence of colors. Once that finishes, the Interlocking In A Box is ready.
Please Note
The status LED on the main board provides diagnostic information. Normally, you can ignore this. But, in the event you need technical support, you may be asked what this LED is displaying.
Place your hand over the TrainSpotter detector on one approach to the diamond. Verify the red light on the detector comes on, the status LED on the main board turns green, and the signal on the approach turns green. If the signal does not turn green, check the opposite approach in case the signal connections are swapped.
Remove your hand and verify that the red light on the TrainSpotter detector turns off. Note that the approach signal should remain green.
Next, place your hand over the diamond TrainSpotter detector. Verify that the red light on the detector comes on and the approach signal turns red. Remove your hand and verify that the red light on the TrainSpotter detector turns off. Wait 20 seconds (or more) before proceeding.
Finally, using the opposite approach, repeat the steps above to verify correct operation on that approach.
Congratulations! You've now successfully installed and verified your Interlocking In A Box!
Options¶
The Interlocking In A Box allows you to customize some delay times and light options to suit your prototype and operating needs. These options are set using the DIP switches on the main board.
Delay¶
The delay setting controls how long the Interlocking In A Box waits from the time a train is detected until it gets a green signal. This allows you to simulate traffic on the opposing track or just simply add some wait time to your operations.
The delay time can be fixed or random. In the case of fixed delays, the same delay will always be used. Every time a train arrives, the Interlocking In A Box will wait the selected amount of time. Simple randomized delays pick a delay time from a selectable range of times. Prototypical randomized delays are a bit more complicated, but better represent what would be experienced on the prototype. In this case, the Interlocking In A Box first randomly determines, based on a selectable probability, if a delay will be applied this time or not. In the event of no delay, the signal will turn green almost immediately. On the other hand, when a delay is applied, the delay time will be randomly selected from a programmable range. This behavior better mimics what would be seen on the prototype where a train gets the signal almost immediately when no opposing traffic is present, but has to wait some time, possibly a significant time, when there is opposing traffic.
To select fixed delays, set the RANDOMIZED switch to OFF. Then, set the A, B, C, and D switches as shown in the table below to get the desired delay time.
Fixed Delays
| Delay Time | A | B | C | D |
|---|---|---|---|---|
| 0 sec | OFF | OFF | OFF | OFF |
| 5 sec | ON | OFF | OFF | OFF |
| 10 sec | OFF | ON | OFF | OFF |
| 15 sec | ON | ON | OFF | OFF |
| 20 sec | OFF | OFF | ON | OFF |
| 25 sec | ON | OFF | ON | OFF |
| 30 sec | OFF | ON | ON | OFF |
| 35 sec | ON | ON | ON | OFF |
| 40 sec | OFF | OFF | OFF | ON |
| 45 sec | ON | OFF | OFF | ON |
| 50 sec | OFF | ON | OFF | ON |
| 55 sec | ON | ON | OFF | ON |
| 60 sec | OFF | OFF | ON | ON |
| 65 sec | ON | OFF | ON | ON |
| 70 sec | OFF | ON | ON | ON |
| 75 sec | ON | ON | ON | ON |
To select randomized delays, set the RANDOMIZED switch to ON. Then, set the A, B, C, and D switches according to the tables below, depending on whether you want simple or prototypical random delays.
Simple Random Delays
| Delay Range | A | B | C | D |
|---|---|---|---|---|
| 0 to 10 sec | OFF | OFF | OFF | OFF |
| 5 to 20 sec | ON | OFF | OFF | OFF |
| 15 to 30 sec | OFF | ON | OFF | OFF |
| 30 to 60 sec | ON | ON | OFF | OFF |
Prototypical Random Delays
| Probability | Delay Range | A | B | C | D |
|---|---|---|---|---|---|
| 10% | 15 to 30 sec | OFF | OFF | ON | OFF |
| 30% | 15 to 30 sec | ON | OFF | ON | OFF |
| 75% | 15 to 30 sec | OFF | ON | ON | OFF |
| 10% | 30 to 60 sec | ON | ON | ON | OFF |
| 30% | 30 to 60 sec | OFF | OFF | OFF | ON |
| 75% | 30 to 60 sec | ON | OFF | OFF | ON |
| 10% | 60 to 120 sec | OFF | ON | OFF | ON |
| 30% | 60 to 120 sec | ON | ON | OFF | ON |
| 75% | 60 to 120 sec | OFF | OFF | ON | ON |
| 10% | 180 to 300 sec | ON | OFF | ON | ON |
| 30% | 180 to 300 sec | OFF | ON | ON | ON |
| 75% | 180 to 300 sec | ON | ON | ON | ON |
Timeout¶
The timeout is used to cleanly handle some special situations. One such situation is when a train pulls up to the diamond, triggering a TrainSpotter detector on the approach, but then backs away, never crossing the diamond. In this case, when the TrainSpotter detector is uncovered, the timeout timer starts running. If the diamond detector is not triggered before time runs out, then the Interlocking In A Box will reset and the signal will return to red. This prevents locking up the diamond indefinitely.
Another situation where the timeout is used is when the diamond detector is uncovered before the TrainSpotter detector on the opposite approach is triggered. This is similar to above, where a train approaches, enters the diamond, but then backs out without fully crossing to the other side. In this case, when the diamond detector is uncovered and the timeout time expires, the system will be reset.
The timeout time is set using the E and F switches according to the following table.
| Timeout Time | E | F |
|---|---|---|
| 15 sec | OFF | OFF |
| 30 sec | ON | OFF |
| 45 sec | OFF | ON |
| 60 sec | ON | ON |
Searchlight Emulation¶
By default, the Interlocking In A Box is set up to emulate the operation of typical signal heads with two independent sets of lights. Or, in the case of Pennsylvania position lights or B&O/N&W color position lights, drive two lights around the outside of a disk. Regardless, the logic will fade one in as the other fades out.
Searchlight-type signals, such as the Union Switch & Signal types H, H2 and H5 as well as the General Railway Signaling SA type, used a signal lamp with a set of mechanically-changed color filters inside known as roundels. Three roundels were mounted on an armature that could be moved by electromagnetic coils. When unenergized, the arm sat in the middle and placed the red filter in front of the single lamp. Green would be on one side. By energizing the coil, it would pull the arm to the side and place the green in front of the lamp.
This leads to interesting effects when changing aspects. Going from red to green will result in a bit of flickering as the armature bounces around before settling. The Interlocking In A Box emulates this rather precisely. If the SEARCHLIGHT switch is set to ON, this bouncing and flashing will be reflected in the signal output giving a very prototypical appearance to model searchlight signals.
Advanced Use Cases¶
Bypassing the LED Resistors¶
The Interlocking In A Box includes resistors to protect your signals against excessive current that will destroy them. There may be use cases where your signals already have resistors installed, or you want to change the resistor values used, and you need to bypass the resistors on the board. There are solder jumpers provided to let you do that, but be very sure that you know what you're doing before using them.
Don't Destroy Your Signals!
Be sure you really need to do this before even considering bypassing the onboard current limiting resistors for the signals. You must install external resistors before bypassing the onboard resistors, or the current will blow up your signal LEDs!
JP1 and JP2 on the back side bypass the resistors for Signal A red and green respectively. JP3 and JP4 bypass the resistors for Signal B red and green respectively.
If you just wish to dim your signals further, we recommend adding additional resistance between the terminal block and the signal, and leaving the onboard resistance alone. Then, if for some reason your external resistor gets shorted or you forget to put one in, your signal is still protected against overcurrent that will destroy the LEDs.
Specifications¶
Input Power: 6 to 24 volts DC, AC, or DCC
Input Supply Current: 25 milliamps @ 12V (typical)
Size: 3.75"(L) x 2.25"(W) x 0.5"(H) (main board)
Open Source¶
Iowa Scaled Engineering is committed to creating open designs that users are free to build, modify, adapt, improve, and share with others.
The design of the CKT-IIAB hardware is open source hardware, and is made available under the terms of the Creative Commons Attribution-Share Alike v3.0 license. Design files can be found in the ckt-iiab project on GitHub.
The firmware for the CKT-IIAB is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or any later version. Firmware for the ckt-iiab can be found in the ckt-iiab project on GitHub.