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
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.
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:
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.
Solder the components to the board in the following order:
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.
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.
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.
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