Experimental MicroMod "T3.2" board

Next step in my deep dive into the MicroMod stuff was to build a custom carrier board. The compact stepper board can be used with up to four stepper drivers with standard layout (e.g. DRV8825). 1xI2C, 1xSPI, 1xUART, 2x Analog and 4xDigital signals are available on the two pin headers. See #34 for more details. In case someone wants to build one, here a link to the GitHub repo: https://github.com/luni64/mmStep with the production data.

Screenshot 2021-01-16 161443.jpg

I was a bit afraid of soldering the tiny 74pin connector but, luckily, it has two positioning pins which make this much simpler. I tested the board with my MM32 DIY Teensy board (see posts above) and, of course, TeensyStep. Here a video showing 4 steppers avoiding collisions at 2100 rpm ;)

 
Not from me, but it is under MIT, so feel free to ask SparkFun, and probably PJRC :) (According to a comment from the SparkFun CEO on Youtube they already viewed the vid during a company meeting :) )

If you need only one or two, I can build you one but I ran out of bootloaders, so I'd need those from you.
 
Nice job! Based on the thread, I think you soldered the micromod connector by hand, right?

If you make any changes to the carrier board, a few suggestions.
- Support Trinamic based Step Sticks. add the two extra pins that they use and support SPI or UART communication with them. TMC based SSs are so much better.
- Add silkscreen info to make it clear how to insert the SS. inserting a step stick backwards will kill it.
- Rotate two of the step stick sockets so they are all in the same orientation. (sorry, I can't resist...)
- Those screw terminals are interlocking so you can turn 2 1x4 terminals into 1 1x8 and it will align better for assembly. Just move them closer together and continue the pin pitch for all the pins. Then, you only need to buy 1x2s that you can put together in multiples of 2.
 
Thanks a lot for your feedback.

I think you soldered the micromod connector by hand, right?
Click to expand...
Yes, that was surprisingly simple

- Support Trinamic based Step Sticks. add the two extra pins that they use and support SPI or UART communication with them. TMC based SSs are so much better.
Click to expand...
Actually I have a few lying around but never used them. Will give them a try when I find some time.

Add silkscreen info to make it clear how to insert the SS. inserting a step stick backwards will kill it.
Click to expand...
He, he, when I soldered them in I thought "why on earth didn't I add some info on the silk screen" :)

Rotate two of the step stick sockets so they are all in the same orientation. (sorry, I can't resist...)
Click to expand...
I was thinking of this but then decided against it according to the good old "form follows function". Turning them would require to route the motor phases between the pads of the modules which I didn't really like.

Those screw terminals are interlocking so you can turn 2 1x4 terminals into 1 1x8 and it will align better for assembly. Just move them closer together and continue the pin pitch for all the pins. Then, you only need to buy 1x2s that you
Click to expand...
Actually, those small 100mil terminals are not interlocking but one could definitely place them at a 100mil pitch. However, they are not really nice to handle and way to expensive. In a next version I'll replace them by some pluggable 100mil connectors. But I'm probably placing them farther away instead of closer together to allow for larger connectors.

Anyway, the main goal for a next version is to integrate a USB PD chip like the STUSB 4500. I like the idea to control and power everything from one USB line without additional power supply. I'll probably do a generic template with all the power infrastructure and the MicroMod connector which can be used to develop various carrier boards without reinventing the wheel every time.
 
luni said:
Not from me, but it is under MIT, so feel free to ask SparkFun, and probably PJRC :) (According to a comment from the SparkFun CEO on Youtube they already viewed the vid during a company meeting :) )

If you need only one or two, I can build you one but I ran out of bootloaders, so I'd need those from you.
Click to expand...

luni, really nice work, love all the documentation.

Just FYI, for anyone interested, I did some quick back of the envelope estimates and arrive at somewhere around $35 to $45 USD per board if these were to be manufactured commercially, based on a 50 board manufacturing run. Basically, luni's BoM is about $12, at a lower quantity, and assembly is $12 per board, quoted from Screaming Circuits. The PJRC bootloader is $6. Small additional costs would be shipping costs of the components to the assembler and costs to pack and ship the board to the customer and some allowance for returns. Plus taxes, salary, and overhead for the staff. I'm assuming that the BoM price would drop as the quantities increase driving towards profitability at the $35 to $45 price point.
 
luni said:
Actually, those small 100mil terminals are not interlocking but one could definitely place them at a 100mil pitch. However, they are not really nice to handle and way to expensive. In a next version I'll replace them by some pluggable 100mil connectors. But I'm probably placing them farther away instead of closer together to allow for larger connectors.
Click to expand...
Ah, I thought they were 3.5mm. I looked at using 2.54mm but couldn't get even the smallest ferrule in the samples I got so moved up to 3.5mm. Even those are pretty tight with ferrules. I agree about pluggable terminals, much more user friendly. Am moving to them on my next board. Unfortunately, I haven't found any interlocking ones.

brtaylor said:
Basically, luni's BoM is about $12, at a lower quantity
Click to expand...
Is that including the M.2 connector? What disti are you using?
 
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