I think some people might be interested in my latest project. Its still ongoing development, but hardware-side everything is set and maybe someone will point out issues I had not thought of yet.
I wanted to source a HAQ movement for a unique watch assembly, but like many others just could not get my hands on one. Watch manufacturers seem to think this (really not very complicated) technology should be some holy knowledge. Welp, time to get the soldering iron out I guess.
The goal is to fit an existing quartz movement with new electronics that include thermocompensation that can be calibrated to 10 spy or better. The heart of the new circuit board is a low-power microcontroller, in this case a Texas Instruments MSP432 that comes with a 16-bit ADC for accurate temperature readings and is based on a Cortex M4 core which I have some experience with. Temperature is sensed with external platinum RTDs. Although sensitivity is not the best, their excellent long term stability really doesn't leave me any choice here.
"Host" movement is an ETA 955.612, since I need 3V Lithium.
With the choice of the µC comes one problem: available packages are rather large (except the 0.5 mm pitch BGA - but good luck finding an affordable PCB supplier for that). My first intention was, to replace the existing circuit board in the movement, but there is just not enough space to fit everything without sacrifices. Also resoldering the coil is a something I decided I want to avoid. So the solution is a second board mounted between the circuit and the battery holder. Only modification to the original circuit is cutting the coil traces and soldering two tiny wires instead to connect to the addon board. This adds a total of about 2mm to the movement height, but since I like divers and similar bulky cases this doesnt bother me so much.
Right now I am waiting for my PCBs to arrive from the manufacturer to solder everything and start the software development.
Below some images of the addon board and a connector board to easily program the µC and provide a low-jitter pps signal for calibration either with an adafruit GPS module or any other external source via SMA or BNC connector.
And a measurement of the stepper motor signal from the original ETA 955.612. Seems to be pretty standard PWM with 50% duty cycle that should be replicable no problemo. The coil current is measured over a 330 Ohm resistor in series.
From my rough calculations a CR2016 battery should last for 3+ years which can be doubled if a CR2032 fits into the final casing.
Feedback and Criticism is welcome ;)