Where does my car get the time from? It drifts and changes every time I start it up. Every 3 months I have to change it manually by 10ish minutes or more, but it’s inconsistent
[1] https://www.analog.com/media/en/technical-documentation/data...
Most interesting to me in all of my time experiments is looking at my clock frequency over time vs. the temperature. (NTP daemons aim to calculate your actual clock frequency; then they know how far off your internal time is from actual time.) You don't even need a temperature sensor, the clock rate is a perfect analogue.
At that point it's surprising they didn't just deploy a local "time network", with a single master clock distributing time via length-calibrated coax. Approaches like that are really common in television studios.
If you want really good short & medium term stability, it's hard (expensive) to do better than an Oven-Controlled Crystal Oscillator (OCXO). An OCXO has a crystal in an insulated chamber with a heater and a thermocouple. A control circuit uses the heater to keep the chamber at a consistent temperature. Over long periods these still drift.
A cheaper alternative is a Temperature Compensated Crystal Oscillator (TCXO), that combines a control circuit with a crystal, a temperature sensor, and a ROM. The ROM contains a table of frequency errors that crystal had across temperature. The control circuit senses the temperature, reads the error value from the ROM, and tries to correct the crystal's oscillation frequency to compensate for that amount of error. Less accurate and less stable than an OCXO, but much smaller, much lower power, and much cheaper.
For longer-term stability you want an atomic clock, probably a Cesium clock or Hydrogen Maser. GNSS (GPS, Galileo, GLONASS, Baidu, etc) satellites have atomic clocks on board, and broadcast that time. GNSS is based around very precisely measuring the differences in received times from various clocks to calculate location, so it can also be used as a way to get a local time reference with good long-term stability. Unfortunately GNSS does have rather poor short-term stability compared to an OCXO, so GNSS alone isn't perfect. But it's common and reasonably inexpensive to create a "GPS-Disciplined OCXO" where a GPS unit corrects for the long-term drift of an OCXO, but the OCXO provides the actual output signal (thus gaining the good short & medium-term stability).
The NIST SP 1065 Handbook of Frequency Stability Analysis[1] is a go-to text on measuring clock sources.
[1] https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpubli...
This made it possible for the first time to build clocks based on the stable frequency of the incoming A/C supply voltage, much more reliably than those based on the incoming line voltage, which varies quite a bit whether it is A/C or D/C.
This put him on the map as a manufacturer when he went forward to build Hammond clocks commercially.
Years later his engineers encouraged him to consider developing an electric church organ, which would be possible to remain in tune regardless of variations in line voltage themselves.
Hammond was not musically inclined but he did it anyway.
Right up there with the Great Men in the most legendary way.
http://thehammondorganstory.com/
By the time the 1960's came around, almost all new American vehicles were recognized as modern Space Age conveniences, and a factory clock (mechanical analog, naturally) had become almost a universal standard accessory beyond the most budget price points.
There were a couple drawbacks to the factory clocks, they had to be connected to the car battery at all times to keep running, they didn't drain the battery very much at all but still would eventually deaden it if undriven, way worse than no clock. And they depended on the incoming voltage which determined the internal clock motor speed to begin with. Different automotive electrical systems and batteries themselves do vary perhaps 10 percent about a nominal design voltage of 12 VDC. There is no stable A/C in the car that a synchronous motor would need to run on[0].
These now-vintage clocks were self-correcting. You correct them yourself. Actually the same twisting of the knob to move the hands of the clock, which was familiar from earlier non-correcting clocks simply did the job. So they were somewhat backward-compatible. Only the Space Age units had smart enough mechanical ability to take into account how much and in which direction you moved the hands, and adjusted the previous running speed accordingly. If the clock was not very close to correct time when you adjusted it, it would take repeated adjustments over a number of days or weeks to get it to very realistic speed. All it really did was successive approximation. You had to supply your own natural intelligence.
Even at the time lots of drivers never knew this, and there was widespread disappointment over the wildly inaccurate clocks "which were OK when new but went downhill 'through time'". They only added maybe a dollar to your car payment but that was very expensive compared to a highly reliable cheap household clock at the time.
When you think about it, today lots of drivers are not quite up to par when it comes to engaging the amount of natural intelligence that would be needed in many other ways besides timekeeping.
[0] The electrical "vibrator" which provided switch-mode 12VAC which could be stepped up by a transformer to supply much higher voltage to power vacuum tube radios still produced a variable A/C voltage & frequency, dependent on the underlying D/C supply voltage.
Every couple of hours or so you'll hear the click from it rewinding on its own. Unfortunately there's nothing to prevent it from running down the battery and they often need to be replaced due to burn out when the voltage gets low. Essentially the rewinder doesn't have enough voltage to actually wind the clock and the circuit stays closed.
>Well if I had money
>Tell you what I'd do
>I'd go downtown and buy a Mercury or two
Mercury Blues:
https://www.youtube.com/watch?v=QsTfCITzISM
I could really use a Mercury or two about now myself.
The trouble with all the modern cars that have synchronized clocks is that, well, you've already put in an LTE SIM card, so why not send up some telemetry at the same time? And here we are, with cars that are surveillance devices with four wheels.
IMHO, the real failure is when devices make it hard to figure out how to change the time.
so the manufacturer gets to choose between making people apply DST changes manually twice a year, which most people understand and are used to doing for various things, or changing over for DST automatically but being wrong sometimes, which most people won't understand and will complain about.