2 Stamps with 1 Radio Modem?

gizmo

Hi everyone,

I have a design in mind for a science telemetry package that uses 2 basic stamps.
Each stamp needs to manage quite different data, which is acquired at different rates.
One stamp acquires small amounts of data very frequently, the other collects a large amount of data much less frequently.
So, the frequent stamp streams data to RS232 most of the time, then the infrequent stamp jumps in, sends, and waits again.
Is it possible to multiplex RS232 like this with some nifty IC from Maxim?
Or, would a digital relay/switch with low noise work?

Any tips would be appreciated!

Thanks,
John

Lee Harker

John,
You should be able to use the same modem with 2 Stamps. I think it would be best to do the coordination before level shifting to RS232 levels if any. It could be as simple as an OR gate connected to each Stamp's TX line with the output of the OR gate feeding the modem. Here's the important part. The Stamps would have to have a method to direct the sharing intentions. You could use one I/O line on each Stamp as a "busy" indicator. If the line is "busy" then you wait. If they "speek" at the same time it would cause a mess. The messages of course would have to include identifiable info so the reciever would know which Stamp sent the data.
This just addressed the question of 2 Stamps transmitting data. You could also have them both recieve data but that gets a bit more complicated. You'd have to have both Stamps reading the data and have only the intended one reacting to it.

Lee

allanlane5

The 74HCT4053 Mux will act as a 3-pole, triple-throw switch under program control. You could have a single pin 'port request' signal that the infrequent stamp uses to request the port from the 'frequent' BS2. The 'frequent' BS2 could then switch the 4053 so the infrequent BS2 is now connected. The infrequent BS2 then does it's SEROUT. The infrequent then lowers its port request. The 'frequent' then switches the 4053 so it has the line, and resumes its transfers.

The 'common' of the 4053 should connect to the MAX232 chip. And the 'infrequent' can monitor the 'Select' pin so it knows when it is safe for it to transmit.

P.S. After further review, I conclude the 4053 acts as 3· 2-pole, 2-throw switches.· Each switch has an 'S' pin, which selects for that switch if X or Y is connected to Z.· This doesn't change your application -- you'll only be using 1/3 of the chip, which shouldn't be a problem.· And as far as I can tell the connection IS bi-directional, so it really does act like a switch.


Post Edited (allanlane5) : 4/1/2005 3:09:16 PM GMT

gizmo

Thanks for the excellent advice!
I'm amazed at what is possible with these stamps.

Thanks again - I'm sure I'll have more questions...


John