Noise problem in my 1-Wire application


New Member
I'm hoping someone can advise me on dealing with noise in a 1-Wire application that I'm developing.

I have a large oven (5' x 5' interior) with 3 shelves with 5 DS2408 devices (8 channel addressable switch) on each shelf (15 total in a daisy chain). I'm using the DS2408 as a parasite-powered switch sensor as shown on p. 29 of the Dallas DS2408 data sheet. I'm using VB6 and the TMEX DLLs to communicate through a DS9097U-009 to read the state of each switch once a minute and have the devices daisy-chained shelf to shelf. Cabling between devices is about 2' and is unshielded, untwisted cable and the adapter is located in the oven near the first device. Serial cable runs out through the oven to a PC. The oven operates at 120°F.

Everything works great until I turn on the oven fan/blower, then noise becomes a problem with erratic switch states or the devices dropping off the network. Within a sample or two (when sampling every second or two during testing) the devices are all detected and the switch states read properly or at least change to a different state. At worst, the devices drop in and out and are completely unstable.

I've connected only one shelf at a time and seen much better results, but two shelves at once is the limit before noise becomes unacceptable. I can tolerate some noise since I only need to sample every few minutes and can take and compare several samplings to confirm a state change before logging it.

I'm in the process of testing a star configuration with each shelf in a chain and the adapter connecting to the center shelf. I'll use 2' of CAT5 to connect the devices.

In another application where I was using a single DS2408 in an electrical cabinet on a machine with multiple servo drives, I also have problems with noise despite using 25 to 30' of CAT5 from the PC and adapter. Running serial cable into a cabinet and placing the adapter very close to the DS2408 helped but I still have some noise.

Can anyone provide advice or possible solutions to eliminate or reduce the noise I'm experiencing?

Sorry I didn't get back to you earlier. Glad to hear that external power seems to have fixed your problem.