1wirev - what defines the order?

Aquaaddict

Hi,

Experimenting with some DS18B20 1Wire temp sensors, I can get them reading ok, but wonder what defines the order in which they are found?

They always seem to be discovered in the same order, so I presume there is some pattern or rule·there?

Am I correct in thinking that I have to hard code their laser ID numbers into my code to make sure I am always reading the right one? The only other way I can think of is to display a list of devices, and thru some menu system record a users choice of what device should be used for what measurement, and then store the laser IDs against their selected usage in·the ROM?

I have also tried the Par version (parasitic verision that takes it power from the data line), it gets dicovered along with the other regular (no Par) ones, and I can get its ID, but I can never get a meaningful temp reading from it, any ideas? I have tridd different values for the pull up, and 3.3v and 5v, always the same problem.

Thanks,

Ants

JonnyMac

You have to apply power (switched on with another pin, see the Maxim docs) for the parasitic units during the temperature conversion -- a bit of a hassle in my opinion, so I use the regular devices.

Aquaaddict

Ah ok thanks, that solves the Par issue, I think I will stick with the regualar versions a just use an extra wire.

Thanks,

Ants

JonnyMac

I don't do a lot of 1-Wire stuff but for a BS2 -> Propeller doc I'm working on I created my own object; it's lean and easy-to-understand. What it doesn't support, however, is auto-ID of OW devices (because I think that's a lot of marketing bunk <wink>).

obex.parallax.com/objects/491/