20 coils are needed for the relays used on the 10 controller switches.

The coils are made of material that is easily obtainable from local stores. (soft iron square tubing and and copper pipe used for plumbing)

The wire is available from any electrical component supplier.

The dimensions of the coil and the wire diameter can be adjusted to optimise the force of the plunger. (to increase the force, provide more wire tuns in the winding and select a thicker wire)

Cut the 30 mm square tubing in 65mm pieces.

Make square end plates to close up the coil sides. (Use soft iron square washers)

Drill holes in the front end plates to allow for the wire to protrude.

Drill 15 mm holes in the end plates to fit the 15mm coper pipe.

Cut 65 mm length of coper pipe.

Press fit the square end plates to the coper pipe.

Provide isolation to the indicated areas (masking tape) (NB: Isolate wire with tape where it passes through the holes in the end plates).

Add the copper wire – 500 turns as shown. (Wire diameter size = 0,95 mm)

There is no heat problem. The processor switches the coils on for only 100 ms at a time.

Insert the coil with end plates into the square tubing and press fit it in a bench vice.

Check with a multimeter for proper isolation between the wires and the chassis.

The plunger is made of 12mm soft iron rod of 65mm length.

The Solenoide contruction is shown below.