I’ve just noticed that the MAC addresses on the OpenSpinklers are all the same. As we had been testing them we had them on different network segments through wireless bridges that effectively masked this issue. Now that we have some of them on the same physical network it causes problems.
Would it be possible to make the last octet of the mac address a configurable option through the web interface?
Yes, that’s on my todo list. It’s pretty easy to add an additional option that selects the last field of the MAC. For now, if you need, you can modify the source code and re-flash. The MAC address is specified close to the top of interval_program.pde. Also, in the past I was able to use multiple controllers (with the same MAC) on the same network by using static ip (each controller is given a different ip). This might depend on your router, but I was able to access each individual controller without a problem.
Fortunately for the time being I can keep multiple timers on network segments behind wireless bridges. On these bridges I have added a script that is flushing the arp cache on the wired network once per second. This is obviously a total hack but it should suffice until a configurable MAC address is possible.