[Swansea Hackspace] 3D Printer electronics

[Justin Mitchell]

> Just found circuit diagram,
> 
> http://reprap.org/mediawiki/images/7/7d/Melzi-circuit.png
> 
> we could simply re-map Hot end to the AUX header, and change code in micro
> ??
> 
> Hot End on PA7 -> PA4.
> 
> just need a 4K7 resistor !!
> 
> Bit concerned that ALL sensors have 4u7F caps on them !!
> 

Having poked around the circuit diagram for the Melzi some more, it
turns out that EXT-A4 is also where the debug LED is wired on the board,
so marlin has that configured as an output, and it has resistors on it
etc.

I have moved the temp sensor parts to a pin header so that i could more
easily change which input they connected through to.

With the thermistor remapped to A3 i now get plausible temperature readings

Should now be possible to reassemble the printer with the old board
whilst we work on repairing the larger board required for the upgrades
to be fitted.