These instruments, for which the diagram,
components list and labels are available below, came about through my
involvement with the superb "00" gauge model railway, Penhallick. Penhallick is an exhibition layout some 55 feet long, with the operators about 45 feet
apart. A means of contact between the two ends was required, but block bells were ruled out as they are not very
practical in an exhibition - especially if adjacent layouts were to use them!
The solution was simple, instead of bells why not use a form of train describer? An instrument was made for both
ends, each of which contains a rotary switch and five train "displays", the operation of which is very
easy. When the system is powered up two lights will show, one on each Instrument, indicating Line Normal. Whilst these
are illuminated either Instrument may request permission to send a train. This is done by means of the rotary
switch which, once turned, does three things. A) It extinguishes the Line Normal lights, B) It illuminates a light
on the other Instrument according to the class of train needing to be sent and C) It cuts off the power supply to
the other Instrument's rotary switch so that only one person may ask permission to send a train at any one
time. It is important that once one person has moved his switch that the other end cannot ask for a conflicting
movement. Similarly, if one end has accepted a train, moving the train acceptance switch at the other will cause
all the train accepted lamps to extinguish.
Let's say end A wants to send a train to end B. The operator at end A will check to see the Line Normal light
is illuminated and, if it is, turn his rotary switch to the class of train requiring to be sent. This will
extinguish the Line Normal lights and illuminate the appropriate light on the far panel for the class of train.
Assuming the operator at end B is able to accept the train, all he does is move his switch to "Train
Accepted". This will illuminate a red light at his end, indicating Train Coming From, and a green light at
end A, indicating Train Going To. As the train enters the section the end A operator will move his Train Entering
Section switch, which will cause a lamp to illuminate at each end. The operator at end B, seeing this, will know
the train is on its way and will acknowledge and cancel the Train Entering Section lamp by moving his similar
switch. Once the train has cleared the section, the operator at B replaces his switch from "Train
Accepted" which will cancel the red and green lights. When the operator at A sees his green light has been
extinguished he will know the train has arrived with B and can replace his rotary switch to normal which will
cancel the class of train light at the far end, illuminate the two Line Normal lights and restore power to B's
rotary switch.
Everything is now back to where it started and either operator may request permission to send a train to the
other.
In the photograph above the operator at the Trecarne end of the layout has asked the operator at the Penhallick
end for permission to send a Parcels Train, which has been accepted. The Trecarne Instrument's rotary switch
will be pointing to "PARCELS TRAIN", whilst the Penhallick Instrument's "PARCELS TRAIN"
lamp is illuminated. Penhallick's "Train Accepted" switch is down, causing the red "Train
Coming From" light to illuminate on his panel and a green "Train Going To" lamp to illuminate on
the Trecarne end's Instrument.
The Instruments may be incorporated in a control panel, or kept as separate boxes that can be attached to the side
of a control panel as illustrated here, or to a baseboard, using "keyhole" fixings and screws.
Click here for a short video clip of the Penhallick Instruments (away from the layout) in action:
Low quality, 1.5MB file
Better quality, 5.1MB file.
or here for a diagrammatic view of how the Instruments work.
I have been asked several times why I used bulbs and not LEDs. The answer is simple, using LEDs didn't occur to me when building the instruments! However, if you want to use these they are a perfectly viable option - simply replace the bulbs on the diagram with LEDs of the correct specification.
I used to sell complete kits for these but since moving to New
Zealand it is easier simply to provide the diagram and label files to your specification by e-mail for
people to use/print themselves, or by post if preferred.
What do you get? Labels printed to suit your own particular
requirements and a pair of detailed wiring diagrams. Please note that a maximum of five classes of train may
be accommodated as the rotary switches have just six positions in double pole function, and one position is
used to feed power to the opposite Instrument.
What else do you need?
Solder and cable, a soldering iron and connectors to plug the system into your 12v DC power supply, plus a few
spare hours to put it all together. A circuit tester might be useful, although if the instructions are closely
followed there should be no need for one.
How much? Free gratis by e-mail, or if you wish for a list of components
required plus the wiring diagram and the necessary labels printed with your requirements these can be supplied
for just AUD 18, NZD 20 or GBP10, including world-wide p&p.
How to pay. Payment may be made by bank transfer to a bank in Australia, New
Zealand or the UK, or by PayPal. Details for all currencies on request.
How may I order the Instrument plans and labels? Please send an e-mail to:
with your basic requirements and a dedicated set will be put together to suit your purpose.
David Brown, in Western Australia, has sent a few photographs of his boxes under construction:
