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The Meccano Relay Board
By Gilbert Ghyselbrecht
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Control your Meccano models (or anything else) from your Windows PC!
Take a look at my new MECControl project at

In response to the call for some practical examples of the uses of electronic circuits in Meccano models, I have developed a system called the Meccano Relay Board which provides modellers with several simple means of controlling their motors. In addition, I have designed three mechanisms which make use of this board, and these mechanisms will be the main subject of this article.

The Relay Board

Click to enlarge

The Relay Board
| Enlarge to 640x480 | Enlarge to 1024x768 |

My relay board is in the first place intended to work with one or two of the slotted opto-switch modules which I have used in my Cliff Lift model, but it is also possible to use micro switches.

Further Information A Cliff Lift - Includes a description of slotted opto switches and a photo of the module mentioned above

The circuit is built on a printed circuit board with the dimensions of a 5 x 7 hole Meccano plate. Connections to the board are made using screw terminals, and the power supply for the board is 12V DC.

The motor to be controlled is connected to a relay on the board which has two individual N.O. - N.C. contacts with a switch rating of 5A 250V AC.

The board can be configured by a jumper link to work in one of three possible modes:

  • Mode 1 - TOGGLE
    Activating Sensor 1 will switch the relay on and activating Sensor 2 will switch it off.
  • Mode 2 - MONOSTABLE
    When activating Sensor 1 or 2 the relay will switch on and stay on for an adjustable time from 0.1 to 10 seconds.
  • Mode 3 - ON – OFF
    When activating Sensor 1 or Sensor 2 or both, the relay will switch on.
Building the Relay Board

The circuit diagram and PCB layout of the relay board are available to download from the links below. You could build the circuit on stripboard, but a better solution is to etch a PCB if you have the facilities available to do this.

Downloads Full Circuit Diagram - GIF image format (311kb)
PCB Design - PDF format (440kb)

Figure 2: PCB component layout

Solder the components to the board in the following order:

  • The two wire links. The longest one runs under the 555 IC socket (U2) and so must be placed before this IC.
  • Diodes D1 and D3. Make sure their orientation is correct.
  • Resistors R1 - R6, R8, R9. For R1 and R2, use the holes that suit the resistor size.
  • IC sockets for U1 and U2. Make sure the notch points to the left in both cases. Do not insert the ICs until the soldering is complete.
  • The six jumper pins.
  • Capacitors C1 - C4. For C1 and C2, use the holes that suit the capacitor size.
  • 3mm LED D2. Make sure its orientation is correct.
  • Transistor T1. Make sure its orientation is correct.
  • Capacitors C5 - C7. Make sure their orientation is correct.
  • Cermet potentiometer R7.
  • Terminal blocks.
  • Regulator U3. Make sure the front (with the writing) is facing towards C6.
  • 12V 5A DPDT relay.
  • Insert the ICs U1 and U2.

Sample Mechanisms

Video Clips The Three Sample Mechanisms - Windows Media format (1.63Mb)
Mechanism 1

A crank (Meccano part 62) is fixed to an axle rod, connected with or without gears, to the driving motor of the model. A push button is used to start the movement. The crank turns and will interrupt the light beam in an opto-switch. This will stop the motor. The relay board is here used in mode 1 (toggle).

When using the relay board in mode 2 (monostable), with the same mechanism, the motor will turn intermittently. The stop time is adjustable.

Click to enlarge

Mechanism 1
| Enlarge to 640x480 | Enlarge to 1024x768 |

Figure 3: Wiring the Relay Board for mechanism 1

Mechanism 2

A bush wheel (Meccano part 24) is taped to cardboard and one or more holes are left open. The wheel turns in the gap of the opto-switch. The sensor is connected to a relay board configured in mode 2 (monostable). The output of the relay can be used to switch other motors or lamps etc.

Click to enlarge

Mechanism 2
| Enlarge to 640x480 | Enlarge to 1024x768 |

Figure 4: Wiring the Relay Board for mechanism 2

Mechanism 3

Here I use two opto-switches connected to a relay board in mode 1 (toggle). The motor is connected to the relay output and turns right, then left, then right and so on.

Click to enlarge

Mechanism 3
| Enlarge to 640x480 | Enlarge to 1024x768 |

Figure 5: Wiring the Relay Board for mechanism 3

 Shopping List

0.01μF Ceramic Disc Capacitor   3   08-0232   $0.03   $0.09
10μF 25V Radial Electrolytic Capacitor   1   11-0220   $0.05   $0.05
100μF 63V Radial Electrolytic Capacitor   2   11-0255   $0.17   $0.34
100kΩ Multi-Turn Cermet Preset Potentiometer   1   68-0145   $0.87   $0.87
10kΩ 0.25W Metal Film Resistor   2   62-3474   $1.40
(per pack of 100)
12V 5A Miniature DPDT Relay   1   60-4610   $2.32   $2.32
14-pin Dual-in-line IC Socket   1   22-1721   $0.53   $0.53
1kΩ 0.25W Metal Film Resistor   2   62-3450   $1.40
(per pack of 100)
1N4001 Rectifier Diode   1   47-3130   $0.05   $0.05
1N4148 Signal Diode   1   47-3416   $0.01   $0.01
2-way PCB Mounting Terminal Block   2   21-0471   $0.16   $0.32
3mm Standard Green LED   1   55-0105   $0.09   $0.09
3-way PCB Mounting Terminal Block   4   21-0473   $0.20   $0.80
4001 Quad NOR Logic Gate IC   1   83-0316   $0.25   $0.25
470pF Ceramic Disc Capacitor   1   08-0180   $0.01   $0.01
68kΩ 0.25W Metal Film Resistor   4   62-3494   $1.40
(per pack of 100)
78L05 0.1A Regulator   1   47-3278   $0.26   $0.26
8-pin Dual-in-line IC Socket   1   22-1720   $0.23   $0.23
BC517 Darlington Transistor   1   -   $0.00   $0.00
Jumper Link   1   50-1674   $0.12   $0.12
NE555N Timer IC (Standard 555)   1   82-0336   $0.23   $0.23
PCB Pins   6   54-3900   $2.24
(per strip of 36)
Grand Total   $13.01

Full printer-friendly parts list

Order the above items from Rapid Electronics via our Circuits Shop and help support the Electronics in Meccano website, without affecting the price you pay! Just click on an item for information about it and/or to add it to your Rapid order.

Orders can also be placed by telephoning Rapid on 01206 751 166 or visiting their website at Prices quoted include VAT at 20%.

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Article Information
Topic: Model Studies | Created: 2/11/2007 | Last modified: 2/11/2007 | First published in EiM: Issue 11 (April 2001)

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