MUXing external stepper drivers

MaracMB

Hello,
Can i MUX the En,Step and Dir pins for the external stepper driver ? I guess the breakout boards for stepper drivers would just share the operating 3.3v & GND and wouldn’t be muxed.
I know i have to disable idle current prior to switching...
I would like to do it with analog multiplexer and utilize the unused 100-103 GPIO pins on the Duex5 board for multiplexer control.

I would need only one (13.th) stepper motor, but since 4 GPIO pins can multiplex 16 channels, this might just open new possibilities for me

dc42

In theory, yes if you only need to drive one of the multiplexed motors at a time. You would need to multiplex both the STEP and DIR pins, and keep the drivers permanently enabled. You would need to modify the firmware to set the multiplexer before generating the step pulse.

MaracMB

@dc42 yes, it’s one at a time scenario. For extruders.
Ok, so only step and dir, ok. Even better

Edit the firmware to send signal through GPIO?

I thought of just adding muxing sequence in toolchange scripts...
Like

M84 E4
Dwell for like 500 ms
M42 P100 S1
M42 P101 S0
M42 P102 S0
M42 P103 S0

So this is not enough?
What would i need to change in firmware if that’s not ok?

A Former User

with a bit of luck you might get away with an i2c based multiplexer and sending the commands straight from tool change macros?

dc42

@MaracMB said in MUXing external stepper drivers:

I thought of just adding muxing sequence in toolchange scripts...
Like
M84 E4
Dwell for like 500 ms
M42 P100 S1
M42 P101 S0
M42 P102 S0
M42 P103 S0
So this is not enough?
What would i need to change in firmware if that’s not ok?

Yes, I think that would be sufficient, in which case no firmware changes would be needed.

You would not need to turn the drivers off using M84 if you kept them all enabled. Or if you prefer, you could multiplex the Enable line as well, and use pullup resistors to disable the non-selected drivers. It depends on whether you want the non-selected drivers to be enabled or disabled.

Also, you would not need to multiplex the DIR line. So a single 74HC238 chip to route the step signal may be all you need.

MaracMB

@dc42 thank you

MaracMB

@bearer exactly.

Duet3D, the best thing that happened to RepRap.

MaracMB

@dc42 This is an update to an old topic. I have waited very, very long to get the multiplexer chips on breakout boards. So, yeah, a delay.
But, just want to report that i have success with multiplexing only enable pin. External drivers are daisychained for step and dir and En is muxed.
Mux is controlled with 100-103 GPIOs.

And it works! Such a cool little thing this mux modules.

MaracMB

@Phaedrux i see you find this interesting.
Here are the two videos of how this goes and progresses;

https://youtu.be/huzOSqUWKVg

https://youtu.be/T9Cm7gDEbp0

Now, i just have to wait for couple of additional breakout boards for stepsticks. But proof of concept is done.

Phaedrux

Very cool, thanks for sharing.