I was having a little trouble when I hooked my extruder up. Although everything seemed to be wired correctly I found that I was getting a zero temperature reading. I checked the resistance across the thermister and it seemed to be right. Looking on the internet I found out the 0 reading is given when the extruder board is not connected. I recollected having this problem when I first tested the electronics, see post here, but couldn’t remember how I solved it. All I wrote was that it was something to do with the order I started everything up. A little searching on the internet and I found this post that was very helpful. Following the comments shown there I worked out a starting procedure that works every time.
Start with everything off and disconnected.
1. Start PC up wait for everything to boot up (or if it is already on, leave it on).
2. Power up 12V on Mendel (I really need to connect a switch up to make this easier).
3. Connect USB to Mendel (Could I connect a switch up for this as well, maybe on the +5V line?)
4. Press Reset on motherboard. Wait for motherboard to resume blink.
5. Start RepRap host, some errors are reported (0 temp measurement).
6. Close RepRap host.
7. Open RepRap host again, no errors reported this time, now everything works!
All electronics and hardware up and working. Success sounds like a high pitched whine (where did I put that Pololu board?!)