Clock pulse generator  - Page 1
Forum section: electronics / projects

author: B J
author_rank: Contributor
timestamp: July 11, 2019, 02:37:10 am
content: Looking for ideas for a pulse generator. I want as close as possible to 5.626 KC, or some multiple, as I can get. Looking at crystals and resonators available through normal outlets and just haven't found one I am happy with. This will be built into another piece of equipment. Looking for ideas. TNX

author: Benta
author_rank: Super Contributor
timestamp: July 11, 2019, 08:21:57 am
content: What's KC? kHz?

author: B J
author_rank: Contributor
timestamp: July 11, 2019, 03:08:05 pm
content: Yep --- KC for kilo cycles --- kHz for kilo hertz --- Thousand cycles per second --- All the same

author: mycroft
author_rank: Regular Contributor
timestamp: July 11, 2019, 04:20:38 pm
content: Quote from: B J on July 11, 2019, 03:08:05 pmAlmost... KHz = KC per second. You could have KC per year.

author: Zero999
author_rank: Super Contributor
timestamp: July 11, 2019, 04:27:28 pm
content: Quote from: mycroft on July 11, 2019, 04:20:38 pmBut generally one assumes the standard SI unit, the second.

author: Bassman59
author_rank: Super Contributor
timestamp: July 11, 2019, 05:15:22 pm
content: Quote from: Zero999 on July 11, 2019, 04:27:28 pmKC is Kansas City.I think the standard SI unit for frequency is the Hertz.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 11, 2019, 05:22:30 pm
content: TNX!

author: rstofer
author_rank: Super Contributor
timestamp: July 11, 2019, 05:24:37 pm
content: You don't like any of the circuits you have seen but you didn't describe what it was you actually required. Low frequency crystals and resonators seem difficult to find so dividers are often used but your output frequency may not be particularly handy. You might look into voltage controlled oscillators (VCOs) but they might not be stable enough.There are programmable dividers that first multiply the input by an integer constant and then divide by another integer constant. Sometimes a VCO is coupled with a divider and phase locked loop.'Pulse' can mean a lot of things. Rectangular, cosine squared, dirac, sinc or Gaussian... From the digital domain, the rectangular is the easiest to generate.

author: B J
author_rank: Contributor
timestamp: July 11, 2019, 05:45:56 pm
content: Thanks rstofer. This is going into a larger project where I need the time base, so just need a small circuit to provide it. I would like to just have a crystal do it, in order to keep it small and simple. Haven't found one with a good F yet. Your right on using a VCO and other more complex ideas. I want to "KISS". As far as pulse shape, I am not concerned. Can use almost anything. At this point I am planning on doing some playing with a crystal at 40 KC, and see how far I can pull it with some little additional parts.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 11, 2019, 06:23:11 pm
content: One possibility would be to use a 2.88MHz oscillator (yes they exist, but you won't find many). (Eg: IDT XLH730002.880000X or IQD LFSPXO016125Bulk, both seen on Mouser, currently non-stocked though, good luck!) followed by some binary counter/freq divider dividing it by 512.2.88e6/512 = 5625 (0.02% error)That's the closest I could find with a crystal-based oscillator (2.88MHz crystals by themselves are even harder to find...) and a power-of-two divider.Otherwise you could go for something like the LTC6900:https://www.analog.com/en/products/ltc6900.htmlFrequency set by a single resistor. Obviously not as accurate nor as stable, but that's a workable and very simple solution if its specs fit your requirements.

author: Benta
author_rank: Super Contributor
timestamp: July 11, 2019, 06:49:59 pm
content: Another solution could be a 30 kHz crystal oscillator (the crystal is a standard value).A /16 stage (simple) followed by a x3 stage (a little more difficult) gives 5.625 kHz.This can be done 100% digitally with a divider and gating/flipflop."KC" is really 60s, are you that old? The world uses SI units nowadays, which avoids confusion (as you can see from the first needless threads).

author: B J
author_rank: Contributor
timestamp: July 11, 2019, 07:19:31 pm
content: Right on, Benta. I was going to make some comment about what worked in the past, but didn't think it was worth the comments. You have to go back further. I was well on my way building electronics, with tubes, Hertz, what's that ? ? ? in the 40s. --- Looked at some of the same thoughts you came up with. Hope to get working on it some more this week-end.

author: B J
author_rank: Contributor
timestamp: July 11, 2019, 08:40:28 pm
content: Hi Benta again. Your last comment got me thinking. I liked what you said, just didn't think along those same lines. (Can't find 30 KC crystals) So, -- start with 60 KC crystal (several on Digikey) divide by eight and multiply by three quarters and I have 5625. That will be close enough. Looks good and will work on this weekend. TNX to all

author: tooki
author_rank: Super Contributor
timestamp: July 11, 2019, 09:17:41 pm
content: Seriously, the Hertz was introduced in 1960, fully displacing the old "KC". There's no reason to use that old name other than to be obtuse!

author: OM222O
author_rank: Frequent Contributor
timestamp: July 12, 2019, 02:40:01 pm
content: How about using a programmable PLL? They are available in quite a large frequency range.

author: Benta
author_rank: Super Contributor
timestamp: July 12, 2019, 05:29:38 pm
content: Quote from: OM222O on July 12, 2019, 02:40:01 pmOverkill IMHO.

author: edavid
author_rank: Super Contributor
timestamp: July 12, 2019, 06:55:56 pm
content: You could buy one of these 5.76MHz oscillators:https://www.ebay.com/itm/MF-Electronics-Corp-M1200-5-76-MHz-Crystal-Oscillator-Lot-of-2-/123058667912Then divide by 1024 with a 74HCT4020, 74HCT4040, or 74HCT4060 to get 5.625kHz.(Or you could tell people what you are actually doing, and maybe get even better suggestions.)

author: tggzzz
author_rank: Super Contributor
timestamp: July 12, 2019, 08:14:19 pm
content: Quote from: B J on July 11, 2019, 02:37:10 amSince you think in of, can I suggest that a PUJT oscillator will meet your spec and also use contemporary technology.PUJT is "programmable injunction transistor".