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Step 8: The Sensor - Final Assembly

Assembling the Sensor

The Ring Board and Support Board must now be joined together, mechanically and electrically.

Note that the copper strips on the ring board are on the outside whilst those on the support board are on the inside - see photographs.

Links consisting of short lengths of stiff wire are used to interconnect the boards along the 'hinge'. Initially solder just two such links at the outermost strips. These links provide the initial mechanical connection.

The sensor must be made as light-tight as possible to prevent stray light reaching the LDRs. To achieve this, cut the black foam rubber into three light shields / vibration absorbers as shown in the photograph. These are the same shape and dimensions of the two boards. The 'ring board inner' has a circular hole of a slightly larger diameter than the LDR circle. The 'ring board outer' has a circular hole slightly larger than the washing machine control knob.

Temporarily attach the foam rubber shields with double sided tape to the boards. Place the sensor with on the washing machine and adjust the angle between the boards by carefully bending the hinge until the support board lies horizontally on the top of the machine and the LDRs are correctly aligned over the LEDs. Small adjustments to the LDR positions can be made by carefully bending the legs of the LDRs.

Remove the foam shields.

Install the 16 electrical links being careful not to change the angle between the boards. These are 'back soldered' on the ring board and 'front soldered' on the support board.

Once complete, attach the foam shields permanently using the double sided adhesive film, cutting this to the same shape and size as the shields.

Sensor cover

A front cover for the sensor is cut from the black Plasticard and carefully bent into shape using a heat gun to soften the plastic along the bend location. Attach this to the sensor using double-sided adhesive film on the ring board front shield and by gluing to the right angle header.

Use black insulating tape to cover the edges of the sensor.

Attach the sensor firmly to the washing machine using double sided adhesive film cut to the shape of the foam rubber inners.

Future development could include a 3D printed cover for the sensor.