Wiring External Drives and Duex5

DougJones · 1 Aug 2017, 21:15

I'm looking to drive some larger closed loop steppers so that I don't have to worry about missed steps. I plan on mapping the X, Y1, Y2, Z axis to the external header and using the built in stepper drivers for the extruder. As I don't care about extruder feedback, I'll be using normal NEMA 17 steppers for the extruders.

The expansion header is great as it converts the logic to 5 volts (as the drives i have will not handle 3.3v logic signals). The problem I have is that I ma want to use some features that are not on the expansion header that are on the DueX5 like heaters, fans, thermisters, etc.

I was thinking of creating a custom 50 pin cable that splits out just the pins from for the external drives. I found the 50 pin connector on Aliexpress and I can use a crimper like nobodies business. Would this work?

Am I missing any pins that should be on both devices. Currently, I've got the 5V, 3.3V, ADREF and Ground pins all split to both connectors. As shown, I know the H6 and H7 PWM pins on the expansion header won't work, but I can change it later if I want to.

dc42 · 1 Aug 2017, 21:33

Unfortunately that isn't going to work, because when a DueX5 is connected, the firmware knows that the stepper motors on the expansion bus use TMC2660 drivers, and it drives them accordingly. Even with a firmware change, the unused driver chips would interfere with the status reports from the other TMC driver chips.

Here are some other options:

the latest beta firmware supports 2 additional drivers connected to the CONN_LCD connector
if you use a DuetX2 instead of a DueX5 then you can connect 3 external stepper drivers to the expansion bus
it's possible to remove the last 3 stepper driver chips from a DueX5 and change a few resistors to make it identify itself as a DueX2 so that you can again use 3 external drivers. The additional heaters, fans etc. will still work even though a DueX2 doesn't have them.

Btw the voltage output by the external driver interface board is somewhat less than 5V in practice. It should be possible to get close to 5V out by wiring the + inputs of your drivers directly to +5V instead of to the + output pins provided on the board.

DougJones · 2 Aug 2017, 18:37

Ok. Thanks for the reply. I can use just the breakout board for now. Can I split out the extra thermister and end stop connections? I assume that's not a problem.

I don't think there is any issue, but if i need any additional IO. Is there a way to get it? Are there any SPI IO expansion chips that are supported. I'd like to add a Blue laser to the setup later and maybe a chamber heater. Can the heater outputs on the expansion header do this?

dc42 · 2 Aug 2017, 18:47

The forthcoming 1.19RC1 firmware supports an additional SX1509B-based I/O expander. However, you are limited to using it for M42, M280 and related commands. You can also tap into the heater and thermistor pins on the expansion connector. However, the endstop pins won't work because they were reassigned as additional SPI CS pins.