Extruder swap

First off I am not a Arduino expert, I can fumble around and usually get my result eventually, however I have never tackled something as complex as the Marlin firmware to the level I am thinking I might need to…

So this is a multi part ask (one is it technically possible with the, second where should I start looking)

I have a TAZ 4 and I have upgraded to a dual extruder and have flashed the firmware as such…

However I also have a E3D v6 Extruder that is set up on a single extruder mount.

What I ultimately like to do, is via the LCD menu be able to:
Swap from a Dual extruder to single extruder config,
Also in doing so I want to change the thermal resistor type to accommodate the the E3D v6, and change the behavior of the secondary extruder fan (to be a constant running fan whenever the extruder temp is over 35c (this is the fan for cooling the extruder) While being able to control the primary extruder fan to operate normally (for PLA or other printing benefited by extruder fan)

What I am looking to do seems easy enough via re-flahsing the firmware each time I change… however major hassle.


There’s currently no way in Marlin to support that level of swapping functionality, as the only way to change the thermistor selection is to reflash the firmware.

Taking that into consideration, if all your hot ends were to use the same thermistor/thermocouple, you could change that once in the firmware, then just swap back and forth later on. Keep in mind however, you’d need to have a thermistor/thermocouple hooked up to the 2nd hot end lead while using the single hot end. Marlin has built in protection so that if a temperature reading it’s expecting to see on one or both hot ends is ever missing, it will error out.

For the always on extruder fan, that line can be found in Configuration_adv.h on these lines:

// Extruder cooling fans
// Configure fan pin outputs to automatically turn on/off when the associated
// extruder temperature is above/below EXTRUDER_AUTO_FAN_TEMPERATURE.
// Multiple extruders can be assigned to the same pin in which case 
// the fan will turn on when any selected extruder is above the threshold.
#define EXTRUDER_0_AUTO_FAN_PIN   -1
#define EXTRUDER_1_AUTO_FAN_PIN   -1
#define EXTRUDER_2_AUTO_FAN_PIN   -1
#define EXTRUDER_AUTO_FAN_SPEED   255  // == full speed

I’m checking on the recommended fan connection.

Would there be any negative side effects of using a " Y" cable connecting one thermistor/thermocouple to both extruder thermistor/thermocouple input connections?

You would have to account for the doubled voltage in the code and if you had one thermistor reading 100c and outputting 1 volt, and a different one reading 200c and outputting 2 volts (or amps or whatever the board reads) you would probably get a board that reported a single hot end being at 150c and 1.5 volts.