Anybody know much about SMTPE

[lonfire]

hi,

I don't know much about SMTPE, but I basicaly need a system where I can play a cd (preferably off a cd player), take the time code from the CD and use it to trigger DMX, MIDI, and have a cable that can carry the SMTPE signal to a set of microprocessors to trigger other things.

 

anybody got any thoughts?

 

rgds

chris

[mikienorth]

I also know nothing about timecode systems except that I have seen what you want to do done, but a more reliable solid state recording was used (hard drive) and triggered pyro (via deadmans cutouts), a hog console, a laser, other sound changes and a bundle of other things I've forgotten now.

Each thing you anted to change had to accept the timecode, which was generated from an apple mac based program. I have some contacts at the old job so may be able to look into it further. Its expensive, that much I do know, and basically negates the need for anyone pressing go buttons on the LX desk, but you still need the LX desk, for example, and someine to rescue it should the timecode collapse mid gig.

[Brian]

Hi Chris

 

is this for some sort of installed system? Something like a theme park ride?

 

Lots of people do this sort of thing but it isn't cheap - have a google on "show control" and a look at Alcorn McBride's website.

 

Are you planning on decoding the SMPTE in the micros yourself? It's tricky but do-able (having done it myself).

 

SMPTE timecode is an audio signal, 80 bits per word, 25 times a second; so that's 2000 bits a second, each of which is bi-phase mark encoded. The effect is you have an audio signal of between 2kHz and 4kHz to decode. The biggest problem is getting an audio signal in a form a micro can process without distorting it. And then you need to consider what happen if the timecode drops out.

[londonjim]

Anyone have any idea how much these units cost?

[ljstevens]

Hi!

 

Have a look at AMX show control we used to use that at a company I used to work at its basically a box of PCI cards but you spec it to what ever you need eg a DMX card, digital sound storage cards, various differents relay cards etc and its all run of a simple pc based programe, unlike the Alcorn Mcbride stuff which is fantastic but its hard to programe. I used a company called Sarna when I last used Alcorn Mcbride stuff, they are very helpful but it really is expensive especially to get your show preprogramed.

[lonfire]

hi,

thanks for the input guys.. after looking around I have got the impression that it would be expensive..

 

changing the idea slightly.. at present I have the micros each with their own timer.. any thoughts how I could ensure that the micros all stay syncronised.. they are all on a local operating network.. I haven't done exhaustive testing on the system but it wouldn't be expected to stay in time for more than 30 minutes.

 

I did have the software on the PC playing the cd and just starting the timers on the micros at the same time as starting the cd.. I am just concerned that if for example the cd jumps or it takes a second to track it will be out of time..

 

needs to be accurate to about 1/10 of a second.

 

I was just thinking that sending an SMTPE signal would be the best way.. but haven't got gazzilions of pounds to spend :-(

 

also anybody know of any cheap cd players that accept an external go signal, or a way to use a non pc audio player but trigger it from the pc or micro?

 

thanks

chris

[Brian]

more questions...

 

When you says 'micros', do you mean small chips like PICs/AVR/8051 or full PCs or somewhere in between?

 

When you say 'network', are we talking RS232/422/485 or a full 10/100 ethernet or somewhere in between?

 

As for using a non-PC audio player - I've seen a simple design somewhere (web maybe or article in mag) that used an IDE cdrom drive and had a small board with a micro on to tell it to play audio track x.

 

Or you could just use a cdrom drive with something wired across the play button.

[lonfire]

hi,

when I say micros I mean 10mhz (they may be 20mhz, can't remember) network enabled processors.. they are actualy 3 processors in one package.. one to handle network coms, one for events and monitoring and one for you application to run on.. the network is a 1.2mbps local operating network.. its technology used for building automation and data collection and such like..

 

I did wonder about using a cd drive to play the cds.. but was hoping for something that might be more reliable.. the system will be used for one off shows.. so each time you use it, it will be with a different cd/track and a different setup..

 

thanks

chris

[Modge]

I did wonder about using a cd drive to play the cds.. but was hoping for something that might be more reliable.. the system will be used for one off shows.. so each time you use it, it will be with a different cd/track and a different setup..

 

thanks

chris

<{POST_SNAPBACK}>

 

I know our student radio station used comersal cd players and broke into the wiring inside to fit remote goes back before they had decent (well better) cd players.

 

As to making micro's talk too each other and stay in sync you've any number of options. As I'm still not fully sure exactly what your trying to do excuse me if I give some options that turn out to be irrelevant.

 

Use what ever data com's standard your using now and have them sync clocks ever x seconds, where x is a value attained by trail and error, or knowing how long it takes for the signal to drift.

 

Use the I(squared)C bus. it has clock sync built in, I've used it my self in labs in my second year.

 

if you PM me I can email you the relevant lecture notes, but they're not publicly avialble.

[lonfire]

hi,

the network is a local operating network.. i.e. its like a mini ethernet, but with smaller packet sizes.. as it happens I use i2c out of the micros to control a couple of devices but this is purely a local coms method (i.e. on circuit board)..

 

thanks

chris

[Modge]

sorry wasn't sure of the sort of thing you wanted