Replace Watch Crystal? - Page 1
Forum section: electronics / beginners

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: April 28, 2015, 04:00:17 pm
content: My chinese 5$ faceless watch gets about 5 minutes behind after a couple days. Is there a standard frequency that these devices use? I cannot see anything on the existing crystal. It is a tiny through-hole can type.

author: DmitryL
author_rank: Regular Contributor
timestamp: April 28, 2015, 04:12:00 pm
content: 32768Hz

author: chibiace
author_rank: Regular Contributor
timestamp: April 28, 2015, 04:25:43 pm
content: might not be the crystal.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: April 28, 2015, 04:39:53 pm
content: I can definitely see china putting an out of spec crystal inside though. There really is not a whole lot else inside other than a battery and a chip to drive the leds.http://cdn.gajitz.com/wp-content/uploads/2009/12/faceless-watch-gadget-gimmick.jpgthis is what they look like, I dont have any photos of the innards.

author: Simon
author_rank: Unknown
timestamp: April 28, 2015, 04:51:46 pm
content: there is a program inside don't forget they may have messed that up

author: SeanB
author_rank: Super Contributor
timestamp: April 28, 2015, 05:29:56 pm
content: LCD or analogue wach you do not need anything digital other than simple dividers and a few nand gates as logic, mostly for setting the time on the lcd version ( ones with the basic time, date and alarm only) and for generating the 1Hz alternate pulses for the others. they use a custom chip for the others, with no spare gates left, as these use power even when not used.Using a MCU makes it a power hog, you want a wristwatch to last a year or more on a single small 377 cell.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: April 29, 2015, 03:06:49 pm
content: Quote from: SeanB on April 28, 2015, 05:29:56 pmThe display is LED, and is off unless the button is pressed, and it displays time, press again for date, again for seconds. After 3 seconds the display turns off. It eats through cr2032 cells in about a month, which is fine as I work as an I.T. and bios batteries are plentifulBut the watch must have some sort of controller as it can display basic text such as 12hr or 24hr and the first 7 segment display uses the top left segment to indicate PM as when displaying in 12hr mode, that segment is either a "1" or nothing so the extra segment does not affect the number.

author: Len
author_rank: Frequent Contributor
timestamp: April 29, 2015, 03:26:35 pm
content: Whether or not it has a microcontroller, it probably has a 32768 Hz crystal. If there is a microcontroller, it could have its own internal oscillator running at 1 MHz or whatever. I've made a clock like that.I've also seen a clock that lost time because of a bad crystal, so that could indeed be the problem.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: April 29, 2015, 03:38:42 pm
content: Quote from: Len on April 29, 2015, 03:26:35 pmAt a price of only 5usd and a full metal wristband, it could happen...

author: SeanB
author_rank: Super Contributor
timestamp: April 29, 2015, 05:32:17 pm
content: If it has something that runs code you can bet it has been run through an optimiasion where every instruction that is not used, and any silicon that is not used, has been stripped out to reduce gate count down to a minimum. It will be a special purpose controller inside, totally dedicated to doing that one job.If you are making 10k a day ( cheap watches for sure) you want the highest possible yield, so the smallest possible die so you get the fewest defects. For cheap $5 watches the silicon is the cheapest part, the small mechanical parts cost more and the assembly even more.