CogClock

Its called CogClock because of its cog-like movement of jumping from one hour to the next, and for its resemblance to clock drawings in cognitive assessment tests.  (if you fail the test, show the doctor a picture of your home clock -- instant cure!)

It uses a real time clock module to power up once an hour whereupon a sever advances the hour hand to the next position.  In its pause state it draws about 160 micro amps and should last over a year on low self discharge rechargeable AA NiMh batteries.  The minute hand is driven by a separate commonly available battery clock module.  On start up and once a month it establishes a WiFi connection and resets the time to the current NTP value.

The clock hands should be made as light as possible.  I cut out a crude arrow from card stock used some glue as sizing to stiffen it and painted it black.  I made the hour hand from a couple of pieces of thin carbon fiber glued to the servo arm.  You'll need a printer  capable of 280 mm for the body of the clock.

Considerable customization is possible.  The size, font, and position of the numbers are readily modified; however the servo specified is only capable of 180 degrees of travel.  It should be possible to use 360 degrees with the right servo.  The servo needs to be capable of 3v operation and draw as little current as possible.  The only likely candidate I've been able to find is the ElecFreaks EF90D.

Firmware and more circuit information is available on github

More information about its development https://hackaday.io/project/205778-cogclock

Parts List:

• DS3231 RTC

• ESP32-C3 super micro

• DM-S0020 Super Mini Digital Servo

• clock mechanism 6mm thread length

• 3 AA battery holder

• 3 low self discharge NiMh AA batterys

• AO3400  or 2N7000 N-channel mosfet

• AO3401   or BS250   P-channel mosfet

• 2 100K resistors

• 1 1K resistor

• 2 0.1 uf caps

• n.o. push switch

• 1N5817 diode

• 16  pin socket

• 6 pin (right angle) socket

• misc M3 screws

• M3 heat set inserts

• 12 M2 x 6 self-tapping screws and washers