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Part Cooling Fan Multiplexer

Posted by charles1954 
Part Cooling Fan Multiplexer
February 10, 2020 11:34AM
Hi Everyone

I was wondering if anyone could provide the sequence of operation for the cooling fan multiplexer. According to the configuration file comments you can have up to 2,4, or 8 cooling fans. This makes sense since you have 3 multiplexer selectors. This would

give the following: 0,0,0 = no multiplex, single cooling fan, 1,0,0 = 2 multiplexed fans, 1,1,0 = 4 multiplexed fans. Depending on how it is programmed you should be able to have any number of multiplexed fans that can be represented in 3 bits of binary +

the one original fan not associated with the multiplexer. I have not been able to locate any configuration for specifying which outputs are used by the part cooling fan or the multiplexed fans. My best guess on the operation of these fans would be that the

max speed of the fans would be divided by the number of fans. A PID would drive the fans based on some parameter. The PID would ramp the first fan until it reached its max speed. As the PID continued to ramp each fan would be driven to its max speed

before the next fan in the sequence was called for. As the PID ramps down the fans would be slowed in the reverse order.

Knowing the sequence of operation and output configuration will allow me to implement this feature on my printer.

*** EDIT *** ... removed xtra-size formatting ...

Edited 1 time(s). Last edit at 02/12/2020 02:52AM by VDX.

Charles E. Ogden
Re: Part Cooling Fan Multiplexer
February 10, 2020 04:22PM
I don't know what your application is, but if the intention is to turn on more fans as a sensor temperature increases, with each fan running with increased PWM as the temperature increases over some range, then RepRapFirmware already supports this.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Part Cooling Fan Multiplexer
February 11, 2020 01:04PM
Hi Charles,

I'm not familiar with the cooling fan multiplexor that you're talking about. Can you give a bit more context?

However, a multiplexor typically is a hardware device that allows any one of the outputs to be selected, so 000 would turn on fan 0, 100 would turn on fan 4, 110 would turn on fan 6, and 111 would turn on fan 7. Of course, you could have nothing connected to output 0, so that 000 would turn all fans off. But there's no way to have 2 or 4 fans turned on simultaneously. But maybe this device is not a true multiplexor? Or maybe it's not even a hardware device, since you talk about a configuration file?

And I can't imagine why anyone would want 8 part cooling fans. confused smiley

Re: Part Cooling Fan Multiplexer
February 11, 2020 06:43PM
I too would like to hear more about this cooling fan multiplexer, and if this is supported by any newer version of Marlin firmware.

This could allow for more cooling on the hot-end throat as the heat increases and Increasing lifetime of the Teflon tubing inside to throat.

Computer Programmer / Electronics Technician
Re: Part Cooling Fan Multiplexer
February 11, 2020 11:21PM
I too was a programmer and technician for over 30 years. I worked mainly with building automation, but also spent some time with scada systems for water treatment.

I also think hardware when I hear multiplexer. But that does not appear to be the case in these circumstances. I am currently running the newest release of Marlin on a Makerbase MKS Gen L V2.1 control board. Up until a few days ago I had the printer all leveled and calibrated, waiting for Mosfet boards for the heated bed and the two hot ends. Unfortunately when that package showed up it was empty. I figured as long as I had to wait for another shipment I would build a heated chamber for the printer and move all the electronics outside.

But back to the cooling fans.

* Part-Cooling Fan Multiplexer
* This feature allows you to digitally multiplex the fan output.
* The multiplexer is automatically switched at tool-change.
* Set FANMUX[012]_PINs below for up to 2, 4, or 8 multiplexed fans.
#define FANMUX0_PIN -1
#define FANMUX1_PIN -1
#define FANMUX2_PIN -1

This is where I found the first mention of part cooling fans. In the configuration_adv.h file. This starts at line 415 and ends at line 424. It doesn't mention any external hardware, and says it is digitally multiplexed. The only other place I find mention of a part-cooling fan is on line 143.

//#define ADAPTIVE_FAN_SLOWING // Slow part cooling fan if temperature drops

I never found any reference to what temperature drop it is talking about. Thats why I posted this question here. It seems that reprap tends to have Marlins ear. I was hoping that one of the Marlin Devs would come over and give us some insight to this issue. I have searched repeatedly for some info to shine some light on this and come up empty. As far as switching to RepRap firmware, I am not really ready to learn yet another program or firmware just yet. How about it Marlin Devs, are you up for this challenge?

Charles E. Ogden
Re: Part Cooling Fan Multiplexer
February 12, 2020 01:23AM
you might want to take a look at [reprap.org]
Re: Part Cooling Fan Multiplexer
February 12, 2020 09:45AM
While looking around and ran across this post

If this pin works when switching to a different pin then should be able to use this pin as FANMUX.

Computer Programmer / Electronics Technician
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