First Power-Up: The ACI-CD16 Takes Its First Steps

Until recently, the ACI-CD16 existed as a design, a collection of components and an idea shaped by the practical problems we encountered on Holgate.

Now, for the first time, a complete prototype has been powered up and asked to do the job it was designed for.

In the first article in this development series, we explained why ACI decided to create its own 16-channel model railway current detector and the real-world experience that shaped the project.

Read Part One: Why ACI Built a 16-Channel Current Detector

With the final terminal connector fitted to the prototype, planning could finally give way to practical testing.

Powering Up a New PCB for the First Time

There is always a mixture of excitement and nervous anticipation when power is applied to a new circuit board for the first time.

Months of decisions about components, connections and circuit behaviour are suddenly put to the test. At that point, the board either begins behaving as expected—or shows you where more work is needed.

Fortunately, the first signs from the ACI-CD16 were encouraging.

When a small current draw was applied to one of the detector channels, the corresponding occupancy LED illuminated immediately.

That confirmed the first essential part of the design: the board could recognise a very small electrical load and identify the correct occupied section.

From the Detector to DCC-EX

Seeing the LED respond was an important first step, but local indication is only part of the job.

The occupancy state also needed to be reported through the I²C interface and recognised correctly by the layout-control system.

DCC-EX EX-RAIL responded when the detector changed state, confirming that information was passing successfully from the detection circuit, through the board’s input interface and into DCC-EX.

For the first time, the complete chain was working together:

• A small current draw was applied to a detector channel.
• The ACI-CD16 recognised the occupied section.
• The appropriate status LED illuminated.
• The occupancy state was reported through I²C.
• EX-RAIL responded to the change.

Seeing the hardware and software respond together was a satisfying confirmation that the underlying concept behind the ACI-CD16 was sound.

A Successful First Test Is Only the Beginning

It would have been easy to stop at that point and describe the first prototype as a success.

However, proving that a circuit works for a few moments is very different from proving that it is ready to become a product.

The detector was therefore left operating while we monitored its stability, temperatures and general behaviour over a longer period.

Occupancy detection continued to work correctly, but the extended test revealed something that needed further investigation: several components were becoming noticeably warmer than expected.

After reviewing the circuit, we identified a number of component values that needed to be revised before development could move any closer to production.

Whether this resulted from a design oversight or simply an incorrect value that escaped the original checks, finding it now is precisely what prototype testing is for.

It is far better to discover and correct an issue on the development bench than after a product has reached a customer’s layout.

What the First Prototype Proved

Although the prototype identified an area requiring revision, the most important parts of the design behaved as intended.

• Occupancy detection operated correctly.
• The board recognised a very small current draw.
• Each tested channel provided clear local indication.
• I²C communication operated successfully.
• DCC-EX received the occupancy information.
• EX-RAIL responded correctly to the change of state.

The required revisions concern component values rather than the physical layout or overall dimensions of the PCB.

An updated version of the board has now been ordered. Once it arrives, the same tests will be repeated before we move on to simultaneous channel testing, different locomotives and longer-duration operation.

Enclosure Development Has Begun

Because the revised component values do not change the board dimensions or connector positions, the mechanical side of the project does not need to stop while the updated PCBs are being manufactured.

Work has therefore begun on the enclosure that will eventually protect the electronics beneath the layout.

The case will need to do more than simply cover the PCB. It must keep the terminals accessible, allow the channel indicators to remain visible and provide clear identification without making installation unnecessarily difficult.

Developing the electronics and enclosure in parallel allows the project to continue moving forward without rushing the testing process.

Every Prototype Teaches You Something

Product development is sometimes imagined as a straight line from an idea to a finished item.

In reality, it is usually a series of smaller steps. Some are exciting, some are frustrating and occasionally they are both at the same time.

This prototype has already done exactly what it needed to do.

It has demonstrated that the detector can recognise a small current draw, identify the occupied channel and pass that information successfully to DCC-EX. It has also revealed an area of the circuit that needs to be improved before the design can progress.

That is not a failure of the prototype process. It is the prototype process working properly.

ACI-CD16 Development Progress

• Completed: Practical requirements identified through Holgate.
• Completed: Initial circuit and PCB designed.
• Completed: First prototype assembled and powered.
• Completed: Initial current detection confirmed.
• Completed: I²C and DCC-EX communication confirmed.
• In progress: Component values revised.
• In progress: Updated prototype boards being manufactured.
• In progress: Enclosure design and fit testing.
• Next: Multi-channel and long-duration reliability testing.
• Later: Final specification and production decision.

What Happens Next?

When the revised boards arrive, testing will begin again from the first power-up.

We will confirm that the component changes have resolved the temperature issue and then continue with broader practical testing, including operation with different locomotives, low-current decoders and several occupied sections at the same time.

The design will only move towards production when we are satisfied that it operates reliably and can be installed, understood and supported as a complete ACI product.

We will continue sharing both the progress and the lessons learned as the ACI-CD16 develops.

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