cold start synchronisation

[buzzer25]

Hi,
I am working on a project using a 32kHz crystal oscillator, i am trying to get a number of identical boards to flash in time with each other. The only connection between the boards is the power supply. I am currently trying to use a delayed boot pulse (using an RC circuit) upon power up to get the boards to sync reliably but it isnt working at present does anyone have any suggestions that could help?
Thanks

 

[ericgibbs]

Hi,
I am working on a project using a 32kHz crystal oscillator, i am trying to get a number of identical boards to flash in time with each other. The only connection between the boards is the power supply. I am currently trying to use a delayed boot pulse (using an RC circuit) upon power up to get the boards to sync reliably but it isnt working at present does anyone have any suggestions that could help?
Thanks

hi buz,
If I understand correctly, each board has a 32kHz crystal oscillator and you want all boards to keep in sync.???

If yes, thats impossible to achieve in practice.

How many boards are they in the project.???

 

[buzzer25]

Hi, yes you understand correctly, each board has a crystal, and boards are normally off, I am trying to get them to be in sync once they are all powered up (at the same time) I am only looking for them to stay in sync for about an hour.

I have 3 boards at the minute, however sometimes they start synced but they often start all over the place. I am looking at increasing the boot pulse length when the are powered up to see if that would help.

 

[ericgibbs]

Hi, yes you understand correctly, each board has a crystal, and boards are normally off, I am trying to get them to be in sync once they are all powered up (at the same time) I am only looking for them to stay in sync for about an hour.

I have 3 boards at the minute, however sometimes they start synced but they often start all over the place. I am looking at increasing the boot pulse length when the are powered up to see if that would help.

hi buz,
Increasing the power reset time will not help.
Crystal oscillators take a little time to start running and with variations in crystals and caps, they will have different start up times.

Also no two 32kHz crystals will run in sync, they vary +/- about the nominal 32kHz

Could you post a circuit showing say, two boards, we may be able to suggest a 'fix'

 

[alec_t]

Depending on the circuitry on the boards, it might be possible to send a sync pulse over the power line.

 

[buzzer25]

I am trying to upload a diagram of that part of the circuit but i am having problems but i will try again later, we do have a external manual boot pulse at the minute for testing which syncs the crystals for approximately an hour, but I am trying to get rid of that. I am also trying to find any more efficient oscillators which may help.

 

[KMoffett]

How about a master clock sending a sync signal over the power bus, and a PPL'd oscillator on each board?

Just a thought...no details.

Ken

 

[buzzer25]

Hi Ken,
by sending a master signal down the power bus would that disrupt power to other components on the boards? This is just a small part of quite a complex board, and sorry for my ignorance can you remind me what you mean by ppl? Thanks

 

[ericgibbs]

Hi Ken,
by sending a master signal down the power bus would that disrupt power to other components on the boards? This is just a small part of quite a complex board, and sorry for my ignorance can you remind me what you mean by ppl? Thanks

hi buz,
Sending a sync pulse on a power line is common practice, its done so that it will not interfere with the supply.

 

[buzzer25]

Ok, that sounds like it maybe the solution i am looking for, I am still unable to attach a picture to for you (the stupid pop up blocker is blocking the page even though it is turned off) but I shall keep trying. Is there anyway you can give me some details on how to put the sync pulse on the power line?
thanks.

 

[KMoffett]

.... can you remind me what you mean by ppl? Thanks

PPL=phase locked loop
There are a lot of tutorials. Google: phase locked loop tutorial

Also, Google DC power communications
for things like: https://www.techbriefs.com/component/content/article/2487

Ken