Newbie - wiring 1-wire network with 6 port master hub

[pkdotnet]

Hello,

I am working on my first 1-wire network. So far I have been able to read temperatures from a few DS18S20 sensors on a breadboard. Lots of fun!

I am getting ready to construct the first leg of the network. I am not an EE, and really haven't played much with components in the past, so I have some questions about resistors.

I will be powering the sensors on pin 3 with the 5V provided by the master hub. I see that to do that, I need to provide a pullup resistor between the 5V and the DQ line. A couple of questions:

1. Do I only need to do this once on the network? Or do I need to do this at each sensor?
2. What resistor should I use? I've heard 4.7K, but then I've seen other people say that's too high.

Finally, I was wondering if I need to provide a resistor inline on the 5V line (pin 2 on the Hobby Boards wiring diagram), or does the master hub limit the amount of current on the line? If I need to provide one, I have the same two questions: only one for the network (pretty sure yes)? and what size?

Thanks for your help (and patience).

pk

 

[darryl]

I wired my sensors directly to the hub. No resistors.

 

[johnboy70_99]

I think I used 100 ohm in series when needed. If you wire it "bus style" you may not need resistors. I wired hub and spoke, and I found if there was a big difference between the distance of two runs (I had one 100' and one 10') I would get problems. From researching this it seemed to be from "reflections" and interferenced caused by the wire length being different. I added 100 ohm resistors in series with the short runs and my problems went away.

If you are doing hub and spoke you can connect and init one at a time, and add resistors if the controller does not pick up the new sensor, or if it loses old ones when a new one is attached. It took just a little trial and error but once it was up and running I have 12 sensors going with no problems.

 

[ericvic]

You should never use a resistor between the +5v line and the DQ line. Since you are4 using a Hub you shouldn't need any resistors at all. If you want to power the DS18S20 then just wire the pins to DQ, GND and +5v with no resistors.

Eric

 

[pkdotnet]

Awesome. Thank you all for the replies!

When I wired up a sensor to an Arduino a few months back, I fried it because I didn't have a resistor inline. Acknowledging that is a different beast from the master hub, I just didn't want to make another newbie mistake.

pk

 

[pete_c]

Have a quick read here. Its a very informative document relating to 1-wire devices, topology ,etc.

1-Wire Guide