1-Wire Technology & Multi Screens?

McGreggor · Post by **McGreggor** » Thu Feb 19, 2004 5:13 am

Is there any limit to the length of wire used for the 1-wire temp sensors? Also, is there a limit to the number of usb lcds that can be used on a single system? I am planning to install a PC in my car, with at least 3 lcd screens, one maybe monitoring the car's water/oil temps. I know you can run more than one instance of LCDC but how does this perform in the real world, do you have to manually tell each copy of LCDC which screen to work with each time the system boots?

Thanks in advance..

P.S Are there any other 1-wire sensors that work with the lcds or is it only temp sensors?
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Paradigm · Post by **Paradigm** » Thu Feb 19, 2004 10:11 am

We've tested cables upto 1m (3ft) in length, but we have heard of people having 1-wire work with much longer cables. It depends on too many factors including:

- How long each cable is - You might be able to get away with a single probe at 20ft but two probes at 20ft might not work
- The environment - The inside of a car is filled with a ton of EMF which will be picked by the cable. The longer the cable the more it picks up, and the more it is likely to interfere.
- Your network topology - There is nothing saying that you have to wire each sensor back to the display. You could have a single cable with multiple sensors branching off of it. As long as all the 5V / Gnd / Data wires are put together correctly you can arrange them any way you like.

With all these factors it is impossible to know what the maximum will be. So we tested 6 probes each with 1m of cable and know that works. Anything beyond that you'll just have to try and find out

Let us know what happens, we love to hear what customers are doing with our products.

As for other 1-wire devices, head over to http://www.maxim-ic.com/1-Wire.cfm and take a look. They have D-A converters, pots, memory, clocks, and more. You'll have to write your own software to use anything other than temp probes, but the display will talk to them.

EDIT: Updated the URL. One too few w's in it

McGreggor · Post by **McGreggor** » Fri Feb 20, 2004 8:34 am

Brilliant, just what i needed to know. I think if i do run into problems with EMI, i can shield one twisted pair cable to the engine bay and branch off the sensors from there.

One thing though, that link doesnt work.. domain name aint recognised..

What about running multiple screens though, am I going to be able to set it up so that 3 copies of LCDC boot up with windows, and each instance of LCDC works with the same lcd each time?

Post by **Mat-Moo** » Fri Feb 20, 2004 8:57 am

McGreggor wrote:What about running multiple screens though, am I going to be able to set it up so that 3 copies of LCDC boot up with windows, and each instance of LCDC works with the same lcd each time?

Yes each copy of LCDC is independant, and there settings remembered.

Paradigm · Post by **Paradigm** » Fri Feb 20, 2004 9:57 am

If you have a good shield that is hevily grounded with two good conductors, you will reduce your EMI problems. Just don't skimp on the quality of the cable. One option would be to use good coaxial cable. Each has only two conductors, so use two cables. Ground each of the shields and deliver +5 and data on the center conductors.

And I edited my original post to correct the URL, it should work now.

Miles · Post by **Miles** » Fri Feb 20, 2004 11:36 am

If you do run into a problem with intermittent communication problems, it is likely due to bad ground or extreme electrical noise. All wires should be sufficient in gage - larger diameter wire is better if there is noise in the environment.