Digital watches use a quartz oscillator. A small rock that has a characteristc frequency it vibrates at and they use "divide by" circuitry to count the oscillations down to one second. A desk clock is just a watch with a bigger display
[This message has been edited by gfretwell (edited 03-19-2005).]
Re: Where Does the Time Come From?#132113 03/28/0502:57 AM03/28/0502:57 AM
Yeah, Good call Greg, A clock uses a 38kHz crystal to provide the synchronisation. The actual crystals themselves are what we would call Rochelle salts, they oscillate at a given frequency when applied with a bias voltage. One thing I'm short of knowledge on, is how the oscillating frequency is set. Is it the size, type of crystal, like the size of a capacitor plate vs dielectric?.
Re: Where Does the Time Come From?#132114 04/02/0503:09 AM04/02/0503:09 AM
Is there a way to stablize a 555, to be used as a "Tolerable Clock"? - like within 1% tolerance?
I have built a 555 based flasher (drives a 20mA LED), which is in close proximity of a "Kit-Bashed" AC powered Clock (Kit-Bashed being a normal alarm clock w/ digital LED segmented display, removed from original enclosure and placed inside an O-27 scale Caboose).
The normal "½ Second Flashing" of the "Colon" is directed to a Railroad Crossing Crossbuck - which controls alternating flashing LEDs via op-amp.
The 555 based flasher pulse cadence is at least 3x faster, yet does not keep a predictable sync. with the crossbuck.
Just curious if anyone has info.
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
Re: Where Does the Time Come From?#132118 04/06/0504:01 PM04/06/0504:01 PM
Replace the system board. Not an attractive option but the TOD clock is soldered on the board.
There is a chance this could be fixed with a BIOS flash but that would only be if lots of people have the same problem and it is some strange microcode problem. Check the manufacturer's web site. They will have the latest BIOS update (if any)
[This message has been edited by gfretwell (edited 04-07-2005).]
Re: Where Does the Time Come From?#132120 04/10/0508:56 PM04/10/0508:56 PM
A few older motherboards had a trimmer capacitor to tweak the RTC oscillator frequency. You can either do it using a frequency counter (recommended), or turn it a bit at a time, and see if the clock gains or loses time. The usual oscillator frequency is 32.768 KHz.
If you have decent soldering skills , you could try replacing the RTC chip (may be socketed!) or oscillator crystal (if not integrated into the RTC).
A software workaround if you are running Windoze XP is to go into the time settings and enable automatic synchronization, and set it to do so every hour or 2, so the time drift becomes less noticeable.