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The Forever Clock under side pic details ...
Right side: main RTC w battery (DS3232)
Top right: connected to the bottom of enclosure is
the accelerometer. (ADXL335) 1 axis used.
Top center is secondary RTC w battery (DS3231)
Top left: NeoPixel power supply and power input from wall-wart.
Left side: GPS (uBlox) / w antenna
Bottom: 4x20 I2C LCD
Center: Espruino in E Block 3D enclosure.
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Do you notice any drift between the two RTC modules?
Hardly none due to the "daily" GPS updates of both real time clocks.
The DS3232 is a +- 2 PPM device which drifts ~ 0.17 seconds per day and since
this is less than a second per day there is no way to measure it before the next sync update.
(It has to be greater than 1 second to measure the drift or inaccuracy) -
If you could measure the difference in time between the 1pps output of the GPS receiver and the 1Hz output of the RTC then you could discipline the RTC using the ageing offset register. A 1-bit change in the register should change the oscillator frequency by one ppm.
I don't know if espruino could measure time that accurately but you might be able to measure using a sample and hold ADC against a capacitor, or some analogue/PWM capture using the Waveform class? Initiated by an Interupt caused by the 1pps you should have time to work out the error.
Gordon
bob_dvb-
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About
Project: The Forever Clock with diamond gemstones!
Posted by
@user7114
Main Features - powered by the Espruino ...
Special design 3D color/coloured ABS printed enclosure for clock electronics. Also, has custom made acrylic dome for NeoPixel clock face.
No push buttons or switches needed - there is nothing to set!
Two precision, battery backed, real time clocks and one GPS module provides accurate time within +- 1 second of GMT/UTC.
Computer generated NeoPixel "analog" clock hands. Green "small hour hand" and red "large minutes hand". Displays time in 5 minute increments.
Time is always rounded up to the next five minute interval.
Automatic daylight savings time adjustment (DST) for hands free operation.
Two time displays - One NeoPixel "analog" clock ring for room display and one backlit 4x20 LCD for local desktop precision display.
The backlit 4x20 LCD displays the following:
Local time/date.
GPS UTC/GMT.
Local time zone.
DST summer/winter mode.
Month abbreviation.
Day abbreviation.
GPS latitude.
GPS longitude.
GPS altitude.
GPS number of satellites.
GPS fix statistics.
Ambient temperature (F.)
Ambient relative humidity (RH%)
Accelerometer measures tilt/angle for LCD display data switching.
The front of the NeoPixel clock is mostly symbolic due to the design input of a small FEMALE. The yellow stars represent the US Military GPS satellite system "in the stars". The blue globes represents planet earth. The diamonds represent "forever" ("Diamonds are forever" [fake acrylic rhinestones]). Hence, The Forever Clock. This forever clock will only fail to keep precision time only when the US Military GPS satellite system cease to exist and the probability of this happening is near zero.
Below is a picture of The Forever Clock without the front bezel and acrylic NeoPixel clock
dome.