1 wire network

[guy45]

I have a 1 wire network using a DS9490R usb master and 8 DS18B20’s.
I am using 25 feet of cat 5 cable running to two 5 port RJ11 jacks to connect the sensors to the master. I also have a 100 ohm resistor on each of the sensors.

I wrote a java program to get the temperature every minute and display it on the screen, then save the temperature to a log file. The problem I am having it takes 12 seconds to get the data from the 8 sensors and when I try to connect 10 I get lots of errors.

I am looking for any ideas that might speed up the time to get the data and ways to add more sensors. This is my first attempt to make a 1 wire network. Thanks for any help you can give me.

 

[ericvic]

Make sure you are wiring in a dasiy chain fashon and remove the 100 ohm resistors. Wiring in a star topology without a Hub can cause reflections and using too much resistance can slew the 1-Wire signal. Both of those things are very bad for reliable 1-Wire communications.

Eric

 

[midon]

2 things to consider; 1. try and remove 8 of the 100 ohm resistors and use 2 only in the legs returning to the master from the 5 port connectors. 2. change *all* the sensors to local power mode to speed up the cycle time. In parasitic mode, you need to send the ConvertT command to each sensor independently, wait 850mS each and read one temperature. If all are locally powered, then you can broadcast the ConvertT command to all, wait 850mS once and then just read each sensor's temperature without waiting again. The caveat is that you must have all sensors locally powered. One left in parasitic mode will cause issues.

If #1 doesn't work, add a hub.

Mitch