The Meccano Relay Board
By Gilbert Ghyselbrecht

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

The Relay Board
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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)

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.

Mechanism 1
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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.

Mechanism 2
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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.

Mechanism 3
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Article Information
Source: Electronics in Meccano - www.eleinmec.com | First published in EiM: Issue 11 (April 2001)
Topic: Model Studies | Created: 11/02/2007 | Last modified: 02/11/2007

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