Dividing a clock signal significantly - Page 1
Forum section: electronics / projects

author: Annakin4
author_rank: Contributor
timestamp: April 18, 2015, 10:58:24 pm
content: I'm working on an electrical engineering project inside my high school. Is there a way to divide a signal from this to the point that a crystal oscillator, preferably at 16 mhz, could go through a circuit and only pulse at a short 2 herz. (2 times a second) Without much delay. Another thing is, we have multiple nodes with these same clocks and they all need to be very accurately synchronized. How would you go about doing that too?

author: Dave
author_rank: Super Contributor
timestamp: April 19, 2015, 12:09:30 am
content: The simplest way I can think of is using a small microcontroller or a cheap CPLD. Why 16MHz, though?

author: georges80
author_rank: Frequent Contributor
timestamp: April 19, 2015, 12:25:47 am
content: Quote from: Annakin4 on April 18, 2015, 10:58:24 pm"without much delay", "be very accurately synchronized"... waffle waffle waffle..."How would go you about doing that too?"How about providing some REAL specs of what you require, then you may get some useful responses... i.e. actual max delay times, skew between various outputs, drive requirements, signaling levels, number of outputs etc...cheers,george.

author: amyk
author_rank: Super Contributor
timestamp: April 19, 2015, 12:50:42 am
content: 23-stage divider will get you 2Hz from 16MHz. I don't know how accurately you want them synchronised.

author: codeboy2k
author_rank: Super Contributor
timestamp: April 19, 2015, 03:45:42 am
content: Quote from: Annakin4 on April 18, 2015, 10:58:24 pmtldr; we need to know what you need, and what you can tolerate for network delays and time clock precisionsYou have to give us specs, like how far apart are these nodes? are they wired , or wireless ? how much precision in the clocks do you need (i.e. you wanted a 2 pulse per sec, or 2Hz clock, and you want all these clocks on each node to be edge aligned, so they all "pulse" at the same time, but that never , ever, really ,happens exactly at the same time.. there's always delays.. and skew between clocks. The question is how much can you tolerate.If you have one clock pulse 100ms early, and other 100ms late, will that be a problem?If these nodes are wired and relatively close by, you can create a master 10MHz reference clock, figure out the network topology (star? tree? point to point daisy-chained?) and as long as you don't exceed your maximum allowed cable lengths (you decide what this is based on how much skew between arriving clocks at each node you can tolerate), then you can divide this clock down at each node to 2 Hz using the same hardware at each node so you get the same propogation delays through the hardware at each node.If your nodes are not wired, or cannot be wired, then you have a few other choices: (1) GPSDO on each node. this will synchronize each clock at the node to the GPS system, but it can be slow to lock (24 hours) and ultimately doesn't work when you are in a location that cannot receive the GPS signal. It is extremely accurate, however ; (2) TCP/IP over WiFi, then use NTP or SNTP to synchronize clocks on the node. This will get you to 50 to 100 ms or so accuracy between node clocks on different nodes . There is also the PTP (Precision Time Protocol) that I think can get accuracies down to the ns level.EDIT: a paper here covers PTP, as well as some othershttps://www.broadcom.com/collateral/wp/StrataXGSIV-WP100-R.pdf

author: Vgkid
author_rank: Super Contributor
timestamp: April 19, 2015, 04:09:44 am
content: using standard logic gates, 3 flip flops(/8), followed by 6 74ls90 to get to 2hz.(/1000000)