An idea that has been in the back of my mind for over 20 years has finally come to fruition over the last 12 months.

I have always wanted to try and replicate the operation of the New South Wales Government Railway’s Miniature Electric Staff (MES) system on the layout.

A brief description of the prototype

The Miniature Electric Staff system was used as a method of safeworking on single track lines and was bi-directional. A staff instrument was located at each end of a section, generally within a manned signal box. Staff instruments could also be switched to “automatic” mode for unmanned locations.

Adjoining sections had different staff types. The correct staff was the token for sole occupancy of a section. Each staff for a section was marked with its identifying number, its type designation and the names of the locations at the ends of the section. The images below show a Type C staff.

The system interconnected staff instruments at the ends of sections, and at some intermediate locations, generally only by two wires, and allowed only one staff at a time to be out of the instruments. The instruments were ‘powered’ by local battery banks in each signal box, and through a series of coils and contacts, provided the electrical interlocking required. The instruments were deemed to be ‘in phase’ to allow a staff to be removed, then were known as ‘out of phase’ and locked until the staff was returned at the other end of the section. The signalman in each signal box used the BELL lever on the instrument to communicate with each other and to place the instruments ‘in phase’. A galvanometer needle showed whether a staff was IN or OUT.

The replica staff instruments

The aim was to enhance the realism of operating my model railway with a very basic replication of how the prototype system worked, so the replicas only indicate if a staff is IN or OUT of an instrument and thus the ‘bell’ and ‘circuit breaker’ functions of the prototype are not used and are purely cosmetic. If a staff has been withdrawn from one instrument, the pair of instruments both lock to prevent another staff from being withdrawn until the withdrawn staff has been returned to the other instrument.

I was able to obtain copies of original railway drawings of the staff instruments and soon realised that I would be able to draw them in 3D and print them. They have been drawn and printed to a scale of 1:2½.

I decided to only reproduce the main head part of the staff instrument as this was all that would be required.

There are four main parts to the replica comprising front and rear sections, lid and a base where the electronics are housed. There are also numerous other printed internal and external components.

Over the last 12 months, with numerous test prints on my Prusa MK3S FDM printer, exchanging ideas with fellow modellers and sourcing non-printable components, I finally had a working model.

I didn’t really want to have to run more wiring between the staff instruments on the layout, so a wireless solution was required. After talking about the project with a fellow modeller in Canada, (thanks Rene), he suggested I look at the ESP32 range of microcontrollers that use Arduino type code. These modules also had built in WIFI.

Now this seemed quite daunting as I had no experience with coding at all, but after joining an online forum, https://forum.dronebotworkshop.com/, I was able to gain assistance from a number of people who knew more about coding than me! In fact, I was lucky enough to have one guy write the required code for me. After sourcing the required hardware and software, and after a few weeks chatting on the forum, I was ready to test the code on a couple of ESP32 modules I had purchased. What do you know….it worked!! I plan to learn more about coding in the future, as I can see a lot more uses of the ESP32 module for a lot of other projects on the layout.

After a few more weeks testing and tweaking both the code and the hardware, I finally had a working prototype.

The operation of the replicas is quite simple. The interlocking between each pair of instruments is done using the ESP32 wifi module and associated Arduino code. Each instrument comprises two small SG90 servos and a miniature momentary switch to detect the removal/insertion of a staff. There is a servo to provide the locking function of the main internal drum and another to provide the galvanometer indication of the staff IN or OUT.

A custom printed circuit board was designed and manufactured to fit within the base of the instrument. There is a 3.3V power supply for the ESP32 module and a variable (set to 5.5V) 2A power supply for the servos. It is powered from a 12V DC source.

Each pair of ESP32 modules are paired with each other using their MAC addresses which eliminates interference to other pairs of machines that may be nearby on the layout.

The replica instruments are designed to hold a maximum of four staffs, but normally if the pair of instruments are ‘balanced’, each would normally hold two staffs.

The replica staffs are 3D printed with a stainless steel rod inside for strength and are painted silver. The plan was to apply decals for the section names etc, but I’ve had problems with them wearing off with use, so I am currently looking into having them machined from aluminium.

Below is a very quick video of the instruments in operation. The galvanometer needles are a bit hard to see, but at the start, they both indicate IN which means the section is clear, and after a staff is removed, they both move to OUT, which has locked both machines to prevent removal of another staff before the initial one has been returned to the other instrument.

I’ll post more on the staff instruments as they are installed around the layout. There will be four pairs in total.

Cheers.