Circling the Square

Board with Bluetooth LE 4

With the version of Lightlog supporting Bluetooth LE 4.0 (BLE), I took on the challenge of laying out the board to fit inside a circle. From the very early prototypes I’ve wanted Lightlog to be circular, but at that stage it was just not practical. Fewer sharp corners is always helpful when it is on something you need to wear, the round shape is also amenable to a wider range of enclosure designs.

The circular board ‘almost’ fits within the rectangle of the previous SMT layout size, but it feels noticeably smaller as its area is much less without the corners. Below is an image of the current circular board layout, a full set of Gerber files can be found over on the Lightlog git repository. There are some power management related changes needed for the next board revision – I’ll try to write a separate blog post on this – but this board is getting close…

LightLog_SMD_0.7_Rev_A

Halving the Size

Checking component layout

It’s finally time to take the plunge and make Lightlog smaller and more robust. Moving away from the hand soldered, through-hole prototype boards, and to a custom multi-layer board using smaller surface mounted technology (SMT). Using specialist PCB layout tools such as Eagle CAD, and the Open Source KiCad, the prototype circuit needs to be re-created ready for a commercial board manufacturer to fabricate.

LightLog SMD v0.6B

Commercial facilities requite a special set of custom files called Gerber files to produce boards with multiple circuit layers, vias (connections through the board), masking of areas from solder, front and back silk screen printing, drill holes, and the final board cutout shape. The image to the right shows the new board design, a full set of Gerber files can be found over on the Lightlog git repository.

The earlier electronics fitted within a box of 29mm x 29mm x 17mm, after these changes the size is down to 28mm x 26mm x 7.5mm. This might not seem like a huge saving, but by more than halving the thickness Lightlog is more discrete to wear and allows a wider variety of potential enclosure designs.

There are a number of part changes with the new board moving to the smaller SMT parts, but one more significant change is the new digital light sensor chip that I’ll try to cover in a future post.

Time to order a batch of these boards of testing!