I have a Printrbot Extrudrboard attached to my Rev. D Printrboard (Printrbot Plus V1)
I have successfully upgraded the firmware despite problems.
I have successfully gotten an LCD controller to work despite problems (not the one I bought from Printrbot, but I know why that one won't work now.)
I am using a dual extruder setup that I had working beautifully with a RAMPS 1.4 board. So I feel confident that the hardware up to the controller was in working order.
I am now experiencing a problem where the second extruder (the one connected to the first port on the Extrudrboard,) experiences greater than 20º C oscillation around the set point. The first extruder, connected to the Printrboard, is rock steady, as is the bed. If I set the extruders for ABS at 235ºC, the Extrudrboard extruder oscillates between 259º C and 211º C.
As noted in the last part of one of Brook's videos on the Extrudrboard, the thermistor for the potential third extruder has to be connected. Despite this requirement, unstated on the website at purchase, one wasn't' shipped and it's one of the few parts I don't have a spare of (I've been a thermocouple kinda guy and have lots of those, but no additional thermistors.) I fabbed up a 10K dummy load (resistor on a plug,) to mimic the 10K thermistor and attached it to the proper plug. This may be the problem, but I'm HIGHLY skeptical since a thermistor is electrically indistinguishable from a resistor in this circuit. Perhaps the value is wrong, but if there is some magic temperature that has to be mimic'd, it wasn't stated in the video. If readers know of any other hidden requirements, I would LOVE to hear them!!
I have run PID Autotune, but while M303 (Autotune) allows specification of the extruder to test, M301 (Set PID values) applies global, not extruder specific values.
Autotune results from M303 E0 S235 C5 (Printrboard extruder):
Kp: 45.84
Ki: 7.52
Kd: 69.84
Autotune results from M303 E1 S235 C5 (Extrudrboard extruder):
Kp: 19.21
Ki: 1.67
Kd: 55.39

Oddly, or interestingly enough, the values from Configruation.h are quite different as well:

#define DEFAULT_Kp 22.2
#define DEFAULT_Ki 1.08
#define DEFAULT_Kd 114
All suggestions are welcome

Thanks!