Boom Gates
Colin Mitchell
Colin Mitchell
June 25, 2016
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Table Of Contents

Parts List

Boom Gates using 2 Servos

Cost: $25.00 plus $6.50 postage [Kits are available](mailto:colin@elechelp.com?Subject=Buying Boom Gates kit&Body=Please e-mail the cost of Boom Gates kit by air mail to my country:****___**** and send details of how I can pay for it. My name is:____)

This project is an “ADD-ON” to Crossing Sound MkII. It controls the raising and lowering of BOOM GATES.
The servo is slowed down to produce a realistic operation.
(Crossing Sound and Boom Gates requires 2 micros. Thus the need for 2 PCB’s)

This is a project you will want to add to your layout.
It activates a set of Boom Gates to produce a very realistic effect by slowing down the output of a servo.
It is added to Crossing Sound project that provides Crossing Lights and Bell.

BoomGates 2
Boom Gates 2

detects a train and produces a pulse to alter the points to alternately divert the train to the siding or allow it to travel ahead.

This project controls the raising and lowering of 2 Boom Gates via two SERVOs.
A SERVO is a motor and gearbox with an output that rotates up to 270 degrees.
By adding an arm (or crank) to the output, we can get linear motion via a “push-rod” to change a set of points.
This project does not operate Peco solenoid points or Tortoise Controllers. It only controls a SERVO.
Don’t get confused with a SERVO and STEPPER MOTOR.
A Stepper Motor produces accurate rotation by means of a directly applied signal to poles (coils) surrounding an armature and by pulsing the coils in the correct sequence, the armature rotates a few degrees on each impulse. It has no internal electronics and generally produces continual rotational movement. A Servo produces up to 270 degrees of rotation and then it generally reverses direction.

  • On-board LEDs indicate “ahead” or “siding”
  • Output to relay to power frog rails

These features are contained in our simple design and can be built in an evening. A kit of components is available from Talking Electronics as well as a pre-programmed microcontroller.

Size-comparison of the TORTOISE Slow Motion Switch Machine and BluePoint with Servo:

Using a SERVO is the cheapest way to automate a set of points and produces fully automatic operation for approx. $25.00

A SERVO is the cheapest way to control a set of Boom Gates.
This project operates the servo slowly to get the effect of a TORTOISE CONTROLLER with the advantage of placing the servo next to the track so you don’t have to cut a hole in the layout or any other awkward installation. It is also much cheaper than any other controller.

This is one of the servo’s we tested. We call it MEDIUM SIZE. The LARGE servos are too big for this application.


Here is the full circuit for the project. You must build the SOUND and BELL section first.

The Boom Gates section is built on the BOOM GATES PC board.
The two infra-red LEDs and two 38kHz receivers are not added to the board as they are on the Lights and Bell PC board.
Here is a photo of the components added to the BOOM GATES PC board and the wiring to the sensors.
Only one of the terminals is used on each of the two blue input terminal blocks.

BoomGatesPCB top
Boom Gates PCB top

BoomGatesPCB Iso
Boom Gates PCB Iso

The Crossing Sound PCB is connected to the Boom Gates PCB with 4 wires as shown in the following diagram:

A very SMALL SERVO uses a micro motor. A Micro Motor is designed “INSIDE-OUT”.
The armature is wound on a former and the turns are GLUED TOGETHER with resin.
The former is then removed and the armature mounted over a strong cylindrical magnet that has a North and South pole, with the North on top and South on the bottom. There are 3 sets of windings, just like a 3-pole motor and the ends are terminated at 3 copper segments called a commentator. This commutator can surround the shaft or be located at then end of the winding. Two brushes touch the commutator segments to deliver current to the windings.
A coreless motor can produce twice the torque of a conventional motor because the armature does not have any iron. The iron absorbs magnetic flux and gets hot.
The armature is also further away from the centre of rotation and this produces more torque for the applied current.
Micro Motors are also known as PAGER MOTORS, where they come with a weight connected to one side of the shaft (called an eccentric weight - not centric). When the shaft rotates, the motor vibrates (as in a mobile phone).
This type of motor can be produced with a case or body having a very small diameter and a short overall length and this allows a SMALL servo to be produced.

The servo in the kit is the MEDIUM SIZE and comes with a set of HORNS. These are commonly called CRANKS or ARMS or LEVERS and connect to the output shaft with a splined connection (grooved) to prevent the arm slipping on the shaft. Some come with a screw to hold the arm in place.
Make sure you get a SERVO with a bag of horns.

  • Servo Arms or “Horns”
  • Single Horn or Arm
  • Star or Cross
  • Double Horn or Arm


The secret to making the servo operate slowly is a program in the micro. It creates a “MARK” (the length of time the control-line is HIGH) that tells the servo to advance (rotate) the output shaft a few degrees. The program then creates a Mark to advance the shaft a few more degrees.
This produces a slow, jerky movement, of the output. Each value is outputted a number of times and this creates the slow motion. You can use an R/C servo or Linear Actuator. CONNECTING THE SERVOConnecting a servo to a boom gates is done using an arm and a push-rod (pull-rod).
The arm and rod turn the rotary motion of the servo into linear motion and the distance traveled by the rod is the greatest when the output of the servo rotates 180°. The distance is called the “THROW” and a number of holes on the arm (also called the “CRANK”) selects the throw to suit the distance needed for the Boom Gate.
The arm and rod is called the “LINKAGE” and this needs to be designed so that the rail sits with a small amount of pressure to keep it in place.
The project is designed to produce about 90 degrees of rotation for the servo. This produces enough “throw” to fully raise and lower the Boom Gate.

Arm positions for PULSE WIDTHS from 500uSecs to 2500uSecs

Most servos will rotate up to 180° and some will rotate to nearly 270°. Our project only needs about 90 degrees rotation to produce a THROW of about 14mm when a push-rod is connected to the correct hole.


Servos come with different colours on the 3-pin connector:

Solder the 3-pin connector in the kit to the 3-wire lead

Solder the 3-pin connector in the kit to the 3-wire lead


The control line is called the “signal Line” and requires a waveform that is classified as a DIGITAL SIGNAL. This means it must rise to about 5v and down to about 0v to for the circuit inside the servo to respond.
The time when the signal is high is called the MARK and the low time is called the SPACE.
The width of the MARK determines the position of the output and it only takes a few cycles for the servo to respond and drive the motor to the angular location where the received signal matches the signal from the input potentiometer.
The signal on the control line is called PULSE CODED MODULATION and the HIGH will vary from 0.5mS to 2.5mS.
The LOW time needs to b e about 20mS.
This means the coded signal arrives at about 50 cycles per second (50Hz).


The Infra red receiver is not just a LED or transistor detector. It is an integrated circuit circuit containing a circuit that detects the Infrared light and only output a signal when the frequency is either 36kHz or 38kHz.
There are two different detectors (such as TSOP4136 and TSOP4138) and the numbering refers to the frequency at which they operate.
Our project transmits at 38kHz and the other detector will not work.



The project needs two micros because two things have to be done at the same time.
The sound is activated during the time when the boom barriers are lowered.
Although the servos do not take up the whole of the micro’s time when lowering, it would be very difficult interleaving the mark-space-ratio for the servo with the sound and lights program.
That’s because the servo program consists of 15uS delays and the sound sub-routine consists of short delays.
Two small micro’s are cheaper than one large micro and so we have a situation of a master-micro and a slave-micro.
The master micro is on the Crossing Sound MkII PC board and since all the outputs are used, we have to take two control lines from the lights section and use them as inputs for the Boom Gates PC board.
Normally, only one of the lights is active at a time so we can look for the first line being LOW and pulse the second line LOW to deliver the activation signal.
These pulses are so brief that the second LED will flash very quickly and not be noticed.


The Platelayers packaging

The Platelayers packaging

Hut Built
The hut fully built

The hut fully built

Looking inside the hut

Looking inside the hut

Place a shim next to the door so the servo can be glued in position

Place a shim next to the door so the servo can be glued in position

Remove the flanges with side-cutters

Remove the flanges with side-cutters

InHut bottom
Glue the servo in position so it does not touch the roof.

Glue the servo in position so it does not touch the roof.

InHut top
In Hut top

Cut a slit in the side of the hut for the push-rod and a wider slit for the wires to the servo. The arm needs to be 2mm from the ground and when the push-rod is fitted into the hole on the arm and the hut placed on the layout, the push-rod will stay in place.

Here are three images to show how the servo is connected to the boom gate. You will need to press the pin into the plastic arm of the boom gate by holding it with a pair of snips and heating it up with a soldering iron so it pushes into the boom gate AND STAYS THERE.
The thick copper wire is included in the kit and will need to be longer than shown to reach from the Plate Layers hut to the boom gate.

BoomGate 1
Boom Gate 1

BoomGate 2
Boom Gate 2

BoomGate 3
Boom Gate 3

Parts List

Cost:$25.00 plus $6.50 postage
[Kits are available](mailto:colin@elechelp.com?Subject=Buying Boom Gates kit&Body=Please e-mail the cost of Boom Gates kit by air mail to my country:****___**** and send details of how I can pay for it. My name is:____)

  • 1 - 1k all 0.25watt

  • 1 - 47k

  • 1 - 100n monoblock capacitor

  • 2 - 100u electrolytic

  • 1 - 1N4004 diode

  • 1 - LM7805 voltage regulator

  • 1 - 3mm red LED

  • 1 - PIC12F629 chip (with Boom-1)

  • 1 - 8 pin IC socket

  • 1 - very small tactile switch

  • 2 - 25cm 2-core flat ribbon (between PCB’s)

  • 2m - 3-core flat ribbon for servos

  • 10cm - 0.5mm tinned copper wire for terminals

  • 2 - 2-way terminal blocks

  • 2 - 3-way terminal block

  • 2 - 3-pin connectors for servos

  • 1 - 20cm very fine solder

  • 2 - Servos and arms

  • 1 - Boom Gates PCB

Colin Mitchell

Colin Mitchell



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