My Homebrew HAQ Project
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  1. #1
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    My Homebrew HAQ Project

    Hi everyone,

    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.

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    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.

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    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 ;)

  2. #2
    Member Mavrobasilis's Avatar
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    Re: My Homebrew HAQ Project

    very interesting!

    what case do you fancy housing the movement?

  3. #3
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    Re: My Homebrew HAQ Project

    Looking forward to seeing your progress.

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  5. #4
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    Re: My Homebrew HAQ Project

    Quote Originally Posted by Mavrobasilis View Post
    what case do you fancy housing the movement?
    Not decided yet, maybe an old Vostok Amphibia if it fits. I think I will try 3D-printing retainer rings for this at some point.

  6. #5
    Member Hans Moleman's Avatar
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    Re: My Homebrew HAQ Project

    Great project.
    Funny how you've got the motivation. "I don't need your permission to buy, I can make this myself"

    We're all getting too lazy just buying ready made stuff.

    Tell me how the temperature correction will flow from the MSP432 to the ETA board. Don't you need to know the internals of the ETA for that?
    ronalddheld likes this.

  7. #6
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    Re: My Homebrew HAQ Project

    Quote Originally Posted by Hans Moleman View Post

    Tell me how the temperature correction will flow from the MSP432 to the ETA board. Don't you need to know the internals of the ETA for that?
    No, the ETA board is completely disconnected and unused. Only the coil must be somehow connected to the new board, and that works best by cutting two traces on the ETA board and connecting two high-current GPIOs from the MSP432 there. Everything from clock generation to thermocompensation and stepper motor control is done on the new board.
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  8. #7
    Member Hans Moleman's Avatar
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    Re: My Homebrew HAQ Project

    Quote Originally Posted by schröder View Post
    No, the ETA board is completely disconnected and unused. Only the coil must be somehow connected to the new board, and that works best by cutting two traces on the ETA board and connecting two high-current GPIOs from the MSP432 there. Everything from clock generation to thermocompensation and stepper motor control is done on the new board.
    That makes sense. Hence the PWM tests.
    I should have picked that up.

    Any plans for asservicement?
    I have no idea how much one can save with that. All of them seem to be doing it.

  9. #8
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    Re: My Homebrew HAQ Project

    Very interesting link, thank you. I actually thought about step detection, but did not pursue this further. Reason is, that the microcontroller would have to stay in active mode a lot longer drawing a lot of current. Even without this issue, the power budget is roughly divided like this: 1 microamp for the stepper motor, 1.2 microamp for the clock generation and 0.5 - 1 microamp for the TC measurements and calculations. So even if the motor current could be cut in half, the overall effect would not be so huge.
    In addition the step detection would probably need a lot of work to reach the required reliability, since even one wrong detection per million steps would decreasy accuracy to 20 spy. Maybe I will think about it again if I do another version. Do you know how the detection is usually implemented?

  10. #9
    Member Hans Moleman's Avatar
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    Re: My Homebrew HAQ Project

    Quote Originally Posted by schröder View Post
    Very interesting link, thank you. I actually thought about step detection, but did not pursue this further. Reason is, that the microcontroller would have to stay in active mode a lot longer drawing a lot of current. Even without this issue, the power budget is roughly divided like this: 1 microamp for the stepper motor, 1.2 microamp for the clock generation and 0.5 - 1 microamp for the TC measurements and calculations. So even if the motor current could be cut in half, the overall effect would not be so huge.
    In addition the step detection would probably need a lot of work to reach the required reliability, since even one wrong detection per million steps would decreasy accuracy to 20 spy. Maybe I will think about it again if I do another version. Do you know how the detection is usually implemented?
    The Witschi document glances over it a bit.

    There are other additional(?) methods being used to check the position of the hands.

    Those corrections on missed steps are quite frequent. They gave me a headache since I use them for rate calculation.

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    schröder and Miguel like this.

  11. #10
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    Re: My Homebrew HAQ Project

    I see, thanks for sharing. This might actually be no too hard to implement, although not immidiately possible with my current board layout. On the other hand I think my next step would be to include an energy harvesting mechanism, probably solar, before working on fine tunings like this. Overall the battery performance would improve by 20% best case - definitly worth a look, but also not the most important thing on the list.

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