The Pluto programmable digital watch is a wonderful project from Lukas / carrotIndustries.
Pluto replaces the PCB of the Casio F-91W with a custom one containing a TI MCU, a digital magnetometer (compass) and a 38 kHz infrared receiver for software updates and communication.
However in 2019 it is no longer manufacturable due to it's magnetometer lack of availability as a standalone component.
This project mainly aims to replace the deprecated MAG3110 chip with the ST-LIS3MDL.
We are also going to try some tricks to make the PCB cheap and easy to get made.
We finally received everything. So we went at our local hackerspace, Electrolab, to solder the first prototype.
PCBs from JLCPCB-> Check
Components from Element14 -> Check
Original F91W (we checked ripoffs, they will not work) -> Check
Help of a friend to use the pick and place machine -> Check
So we started to put solder paste on the PCB with a sharpened toothpick (0402 parts are a thing of beauty and a joy forever), following the really handy interactive HTML BOM.
We thought we would put the MSP430 MCU last since it is the largest part and it could interfere with the soldering of the other components.
First issue, probably a clearance problem. One of the two R2 pads was under the solder mask. We scraped it (yes with all the other passive components already placed of course, note for future self: never trust a quality control from a $2 PCB supplier). It seemed to take solder just fine.
Crossed in blue, the pad in question.
Second issue, after soldering every other component but U4 (damn small and not necessary for the first tests), we tried to place the MSP430FR6972. Or the MSP430FR6972IPM should I say.
Let's take a look at the datasheet shall we?
Always check your packages. Twice.
I ordered some samples from TI to get the first prototype running, with the correct VQFN package.
We had access to a professional computer-controlled reflow oven, devouring 16kW of power, but it was probably just a bit overkill for a single 24mm board. We were glad to be able solder everything with a hot air gun, soldering iron, and a lot of dexterity.
Using too much solder paste is a common problem, featured here.
See you in the next log, hopefully with a working prototype!