A gorgeous batch of one hundred boards, fresh from fabrication! Unfortunately, pretty as they all are, they’re not ready for real-world use :( This batch includes a design oversight on my behalf that prevents them from fully powering down the Bluetooth device while not in use, this significantly eats into the target minimum battery life (usually over four months) leaving between one and three weeks before the battery is drained. Ouch! Luckily I can still build and use a number of these for testing the planned board fix, and move forward with the Bluetooth software implementation and testing.
With the latest circular Lightlog board fully populated with components you can see almost all parts are now on the top side of the board, making it easier to solder them in one go using solder paste (applied using a solder mask stencil). The solder is then heated using a hot air gun from above, or a hot plate from below. Placing components on the solder paste is now the slowest manual step, taking perhaps 10 to 15min, it’s a little fiddly if you don’t have patience and a steady, tweezer hand!
In the image above, the chip at the top is the 64Kbytes of EEPROM memory. On the left of the board is the PICAXE-14M2 micro-controller. The centre and right of the board hold the HM-11 Bluetooth LE 4.0 module (the antenna is on the right edge). Along bottom edge are five white LEDs for indicating the current light goal and ambient brightness. Near the bottom, just above the central LED, is the TAOS TCS34725FN digital colour sensor used for tracking the ambient light and colour conditions.
The components on the back of the board need to be soldered by hand, after the components on the front are soldered, but as there are only two large components it is a quick step to complete. In the image above, the 3V CR2032 battery holder is in the centre, and tactile press switch at the bottom. Pressing and holding the switch down for 2 seconds triggers the LEDs to display your current daily light goal achieved so far, and will attempt to synchronise data via Bluetooth if you’ve linked it to your smart phone, tablet, or computer – the code for this is still a little rough still, but will go up into the git repository (again under an Open Source license as per other parts of this project) once the more obvious kinks are ironed out.
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…