cyborgworkshop.org

I ran into a small problem with WHIA recently that seemed to be fairly serious.  I could only attach two sensors at a time without the whole 1-wire network going dark.  After doing some research and being pointed by Maxim to app note 148 I found that my trouble was based on using a star type topology and parasitic powered sensors. The star topology was necessary simply due to the layout of the sensors. I guess I could have done some weird loop with the cables once they were in the basement, but that was far from ideal. The parasitic power was a requirement because, well, those sensors are free from maxim and it’s what I had on hand.  In the end, I decided to go with a switched 1-wire network. What this means is that currently, each sensor is on it’s own isolated 1-wire network. I tell the arduino to do a 1-wire discovery, read the sensor it finds, then disconnect that sensor and move on to the next network. The whole process only takes 1 second, so not problem at all there.  I wanted to use a common source analog switch of some sort, but had a hard time finding one cheaply that would do what I wanted, so instead I chose to use 1 digital IO pin on the arduino for each network.  My sensor read loop then simply moves from one pin to the next looking for 1-wire devices.  It’s not great and it won’t scale like a true 1-wire network will, but it’s doing a darn fine job at the moment.  I am having one lingering problem. The boarduino that Im using seems to like to reset its usb bus and change what device it’s attached to, so my update script stops working. I think that is just power related though and Im going to try to address it tomorrow.