Synching 2 PICs?

arrow · Joined: 17 May 2005 Posts: 213

Hi Ckielstra, SherpaDoug, and RLScott

Thank you all for replying.

Yes, my specifications are not set (yet).
The accuracy is defiantly relative! All I care about is that the the two PICS are synchronized to each other; I do not care if they drift with respect to an external time clock!

One thing I was thinking of was to reconnect the two PICS after 4 (or 8 hours) and determine how far out they are from each other. Then use linear interpolation. But I would prefer to have the two PICS synced in hardware if possible.

All the best
a.

Ttelmah · Guest

Seriously, if the PICs are in different locations, linear interpolation, isn't going to be that good. It'll correct for the basic differences between the crystals, but temperature, and supply changes, are still going to 'bite'. The best, and simplest solution, is going to be a PLL locked onto a common radio station, or (more complex, but 'better'), the colour sub-carrier on a TV station (better, since the frequency will then be constant, while the radio one - assuming the station is FM, will vary with the signal being transmitted). There are several FM radio receiver IC's, that have the PLL signal available externally, and with only a couple of components, a simple receiver can be built. Even 'better' do the same wth an AM LW station, such as the ones used to send the MSF signals, who often provide 'guaranteed' accuracies on their transmission frequencies. However since it is only relative accuracy that matters, this is not needed. Others have suggested GPS, and this too is a great solution, but the receiver is more complex to make.

Best Wishes

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

If power supply in both units is from the mains and not from a battery you could use the power line zero crossing as a timing signal. Microchip has several application notes showing how to do this with just a single resistor.

horkesley · Joined: 20 Feb 2007 Posts: 48 Location: Essex UK

Lets go back to the start.

Why do you need to do this, what is the application?

I am troubled by this thead.

Regards
_________________
Horkesley Electronics Limited

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

If you are trying to have 2 PICs "simultaneously" measure something, you could have each take a set of measurements. For example take 5 measurements, 2 early, one on time, and 2 late. Then at the end of the experiment look at the drift of the clocks and decide which measurements were actually "simultaneous".
_________________
The search for better is endless. Instead simply find very good and get the job done.

Humberto · Posted: Thu May 22, 2008 10:13 am

This thread is plenty of good ideas but I´m still do not understand exactly the whole project,
I would like to know:
1) Does the boards share something? power supply, common bus, etc.
2) What's the distance between them?
3) What do you need to actuate in such synchronized way? (a valve, a relay, a bomb,
a motor, an actuator, a car engine/security stuff, an intercontinental missile...)

To know what/how do you need to do it and the involved hardware is a must to get better help.

Humberto