61 lines
2.8 KiB
Plaintext
61 lines
2.8 KiB
Plaintext
rtc module
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ds3231
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product page: https://www.adafruit.com/product/3013
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product tutorial: https://learn.adafruit.com/adafruit-ds3231-precision-rtc-breakout/overview
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install packages python3-smbus i2c-tools
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enable i2c support in raspi-config
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interfacing options->i2c->
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enable <Yes>
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kernel module loaded by default <Yes>
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check that i2c-dev is in /etc/modules
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add `dtoverlay=i2c-rtc,ds3231` to /boot/firmware/config.txt
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reboot
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detect/test module `sudo i2cdetect -y 1`
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looking for address UU AFTER configure Overlay
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looking for address 68 BEFORE configure overlay
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remove package fake-hwclock
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remove from rc
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read rtc `sudo hwclock -r`
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set rtc `sudo hwclock -w`
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raspberry pi RTC tutorial: https://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi/set-rtc-time
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pinout: https://learn.adafruit.com/adafruit-ds3231-precision-rtc-breakout/pinouts
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battery: CR1220
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chipset product page: https://www.analog.com/en/products/ds3231.html
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chipset datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/DS3231.pdf
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chipset reliability report: https://www.analog.com/media/en/technical-documentation/reliability-data/ds3231.pdf
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notes:
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https://serverfault.com/questions/1093101/chrony-hosting-time-with-rtc-as-authoritative-clock-on-an-air-gapped-isolated?__cf_chl_tk=G_sZX4ClltOv3fQJpH1q2a65tx4O2s_H_FObeBQ2UyU-1749831141-1.0.1.1-W0v5fl8cCrf0tIpB0pAqIb93L5MuoWeebiHm7iLGAlo
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https://stackoverflow.com/questions/49730407/how-to-do-one-shot-time-sync-using-chrony
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do oneshot sync?
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script set every x seconds
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`sudo hwclock -r`
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GPS module
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baudrates
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1. 115200 // working
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2. 230400
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3. 460800
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cable delay
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cable is 10ft? RG-174?
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14.3
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velocity factors of cable forms
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RG-58: VF ≈ 0.66 (66% of the speed of light)
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RG-174: VF ≈ 0.70
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LMR-200: VF ≈ 0.83
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LMR-400: VF ≈ 0.85
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formula
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CD = time in nanoseconds of cable delay
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L = Length of cable in UNIT
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DF = delay factor in UNIT )speed of light in a vaccum used in nanoseconds per UNIT)
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3.33 = ns (nanoseconds per meter)
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1.016 = feet (feet per meter)
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VF = velocity factor of cable (above)
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CD ≈ (L*DF)/VF
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CD ≈ (Length (meters) * 3.33 (baseline light speed in a vaccum ns/m)) / Velocity Factor of cable (VF)
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derriving the speed of light offset
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t(ns) = time in nanoseconds
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c = speed of light in a vaccum in meters per second (3*(10^8) m/s)
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d(m) = distance to travel in meters
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t(ns) = d(m)/c |