Announcing PrntrBoard V2

Reflecting on the PrntrBoard V1, there are many good things that I managed to accomplish:

    • all 3 versions of the board (2130, 2660 and 2209) were functional
    • the board features were good
    • driver cooling was excellent

When I started 2 years ago, there were very few 32-bit boards with comparable features. Now there is quite a bit of them. I was trying to find what makes one design more popular than the other and in addition to the board features it comes down to flexibility.

In PrntrBoard V1 I was trying to provide superior cooling solution compared to the tiny replaceable driver board used everywhere. However that choice came at the expense of a monolithic design, which was expensive to make and costly to evolve. Every time I wanted to use a different driver chip I had to re-design the whole board from scratch. It was not going to be sustainable in the long run.

Announcing the PrntrBoardV2: combining all lessons learned and expanding the versatility of the design.

First major change is that the motor drivers are no longer part of the board. Because I still find the original Pololu driver form factor very limiting, I designed the motor driver carried boards to use PCIe slots instead of pin headers.

Here is what the carrier board looks like

The board has 32-bit Arm micro controller – my favorite STM32F407. There are 6 stepper motor slots, with support for 6 thermistors or 6 thermocouples (vie external boards).

There are 4 power MOSFET outputs (1 bed and 3 heaters) and 5 low power MOSFET outputs for fans or LEDs.

Connectivity is via traditional USB, micro-sd card. There are 2 more serial ports for a smart LCD controller and WiFi extension.

I have the traditional RAMPS LCD expansion headers, which should support a variety of LCD screen designs.

Last but not least there are 8 end stops and the ability to route the stall detection signal from the steppers to individual end stops or a global “Alarm” signal.

Drivers are on separate boards with PCIe card edge connectors. This is what the TMC2660 version looks like

And this is what the TMC2209 version looks like

I added some mounting holes next to the PCIe slots so the drivers would not wiggle out of the slot with extensive vibrations.

These driver boards are much larger than the Pololu drivers, which would allow for superior cooling and the ability to have more board real estate for complex designs and or big driver ICs.

In addition the driver boards are mounted vertically on the carrier board, which saves space on the carrier board and allow for excellent air flow trough the drivers with a pair of 40mm fans.

Last but not least because of the reduced requirements on the carrier board, I can use 2 layer instead of 4 layer board, which makes the cost even lower.

I can’t wait to make a few of these and run them trough some tests.

Some early experiments with the TMC2209 board

Good news first: I managed to get one motor moving with a simple Arduino sketch.

I’m starting to hate QFN packages with a passion. I spent a whole afternoon trying to re-work two pesky drivers. The chips would not communicate via the UART port, no matter what I tried. Finally traced the issue to a bad solder joint on the QFN package and boy these are hard to spot. Simply re-heating the drivers and re-positioning was not enough, I had to remove the chip, add more solder paste, melt it, then re-insert the chip, wipe the excess solder with a soldering iron and finally re-flow the chip one more time. Complete and total PITA.

To top it off this destroys any near by plastic connectors, so now I have the drivers in-place but have to re-solder the connectors back. This would be an endeavor for the next week.

Now all 5 steppers are communicating with the MCU reliably. I had to add support for half-duplex mode to the stm32duino core. The proposed changes are still pending, but I verified that the TMCStepper library is able to communicate with the drivers.

First prototype of the TMC2209 design

This took me whole day. Working with QFN drivers is plain PITA. It does look good though. I just hope it works.

I finally figured out how to wash most of the flux from the board. It is still not perfect, but looks really good.

I have another revision with 3 fuses. I figured that one fuse for both motors and extruder heaters may be too taxing. In my latest design I have one 15A fuse for the heated bed; one 10A fuse for the extruder heaters and one more 10A fuse for the rest of the electronics.

Added some useful features to my Marlin fork

I maintain a separate fork of Marlin with some tweak that enabled features specifically for the PRNTRBoard. The code is located in github.com .

Last weekend I spent some time adding some minor, but useful updates. First I finally got to enable support for the sd-card reader on the Nucleo-F407 board. It took a while because typically Marlin uses SPI to communicate with the sd-card. However the STM32 has much better hardware module (SDIO) which allows excellent transfer speed.

So it took some time to research what is the simplest way to add SDIO support to the Marlin firmware. There was already support for the STM32F1 series CPU, but it was written using a deprecated library (libmaple). Long story short it is working fine now. The code is in the f407 branch.

The second feature I wanted to enable is the ability to store the printer settings. Usually this is accomplished using I2C or SPI EEPROM chip. Alas I did not add one to the Nucleo-F407 board. I added an SPI flash instead.

The difference is small but significant. EEPROM chips are small, but can sustain millions of data re-writes. In contrast SPI flash chips are relatively large (the one I use is 2MB), but can only support around 100k re-write cycles.

There were two possible approaches, one use the sd-card as storage. This was already supported in the Marlin firmware, so I simply ported to code. The disadvantage is that it depends on the presence of an sd-card in the slot.

The second approach is called wear leveling – using the fact that I have relatively large storage and spread the writing operations across many locations in the chip. This way if I spread the write operation evenly across 100 separate locations I’ll achieve 10 million re-write cycles.

The error leveling code is relatively simple. For the curious you can find the changes here.

Next I finally decider to make a converter board for RAMPS style LCD controller modules. The files are checked in the main PRNTRBoard github repository. I placed and order for a few prototypes – they should be arriving in a week or so.

PRNTRboard update

The TMC2130 version of the PRNTRboard is working very well. I’ve been using it for over 6 months on my soldering robot project. It is very stable and reliable.

I didn’t have time polishing the Marlin firm ware for it. I wanted to make the SD-card work on the F407 Nucleo-64 replacement board. Alas every time I look at the Marlin code, I loose all hope and start doing something else.

A few months ago I started working again on the TMC2660 version. This was the first variant I routed successfully, but I ran into trouble with controlling the drivers over SPI and switched my effort to the TMC2130 version. Long story short, when the TMC2130 was in a good shape I started looking back at the TMC2660 version. It is on rev 5 now and I’m really happy with the layout. In my opinion it looks much better than the TMC2130.

I managed to produce a working Marlin firmware for the TMC2660 board and tested a few motors. So far it works like a charm.

My only gripe is that while the mate black finish looks awesome, it is absolute PITA to clean the solder residue from it. I washed this board 3 times and you can still see some spots on it.

As a kick all thru-hole pins on the Nucleo-F407 board underneath are soldered using my soldering robot. On the TMC2660 I soldered the two headers with the robot.

Last but not least I started working on a version with TMC2209 drivers – these are quite capable and low cost compared to other Trinamic offerings.

TMC2660 success at last

I was very frustrated with my failure to get the TMC2660 board variation running. I checked and double checked the connections, alas the steppers would not move at all.

I purchased one TMC2660-BOB kit from digikey and started experimenting with it, instead of my board. At first, I had the same failure – the stepper would not move at all. The software was a very simple Arduino sketch – what would be that wrong. Since the kit was designed by Trinamic, the hardware should be proper. Alas, no luck. I declared the TMC2660 chip cursed and moved to my soldering machine project.

Yesterday I decided to give the test jig one more try. After a few failed attempts. I spotted an error in the Arduino code – I was passing the incorrect CS pin in the driver setup. DUH!!! After a quick fix it was working.

Then I moved back to my original goal to test the thermal dissipation ability of my TMC2660 PrntrBoard design. I connected my board and started to torture test the motor driver. Unfortunately I was not able to run the driver past 1.5A RMS, which is a shame. I’ll try using a different motor with higher coli resistance. Anyhow here is an image from my thermal camera of the top of the ship:

The chip has no heat-sink and runs at 54C. This is not bad at all. much cooler than the TMC2130 version. The board seems to be dissipating quite a bit of the energy.

Here is a picture of the bottom of the board:

The bottom is at 45C in the center, which I think is quite good thermal conductivity of the board layers.

I feel good about the board thermal capabilities. If I add heat-sinks on the top and the bottom it should be able to run at 2A RMS and above with active cooling.

Soldering machine progress

I managed to put together the chassis of the soldering machine. The bulk of it is made from parts for a Prusa MK3 3D printer. It provides a good start point so I can experiment further.

This is what is looked like in the beginning

I also put this mounting plate to hold the connectors that I need to solder for my test board. With this plate I can insert the connectors, place the board over and get it soldered quickly, then move to the next one.

Here is a video how the head would move along the Y axis

And another one along the X axis. This one needs to hop over the pins.

I used my PrntrBoard controller to drive the motors. This is a picture of the machine in it’s current variation. I added the Prusa LCD display, but have not connected it yet.

Completed redesign of the TMC2660 branch

I spent a lot of time getting the PrntrBoard tmc2130 version to work. I’m at the point where I’m quite happy with it and don’t see major further changes. The tmc2660 branch did not get a lot of attention in the mean time.

So I spent a weekend completely re-designing the tmc2660 board. I ported all changes from the tmc2130 version. There is now a dedicated ground plane layer and routing it much easier.

I opted to put all drivers on one side of the board. Unfortunately limiting the size to 10x10cm (or 3.9×3.9 inches), I could not fit all drivers in one row.  Hopefully cooling would not be major PITA as it was on the tmc2130 version.

Here is a screenshot of the 3D rendering of the redesigned board:

Please excuse my mistake, the top row of power connectors is facing backwards. Fortunately these are symmetrical and I can simply solder them the other way.

Here is a view from the top:

I used very aggressive layout for the connectors and I ended with some spare space in the middle of the board. I was thinking to add two automotive type fuse holders for extra protection. I haven’t quite settled on what fuse holder to use. Here are two renderings with the footprints in KiCAD:

And view from the top:

All changes have been pushed to my GitHub design repository page. The version with the fuses is in the tmc2660-fuse branch.

Controller brain – replaced

While I was working on porting Smoothieware to run on my 3D printer controller, I was going back and forth between my trusted NUCLEO-64 F446 devkit and a new acquisition from china – the “Black VET6“. That was a very capable board with onboard SPI EEPROM, battery backup, micro SD card and USB connector – all this for less that $10 from aliexpress.

While the NUCLEO has the advantage of build-in ST-LINK debugger, I was missing the SD-CARD connector and the extra pins to work with.

The NUCLEO-64 uses only 64-pin micro-controller package and I was running out of available IO pins. For example on the Rev3 of my controller I has to use every last pin to be able to connect an LCD screen – and even then sharing the SPI bus between the screen and the TMC drivers was causing some issues.

Here comes a proposed solution for this issues: a NUCLEO-64 form factor board designed with a 100-pin MCU (STM32F407VE):

This was my very first try and I did not have all parts available yet, so you can see some unpopulated pads.

The board is the same size as NUCLEO-64, and has the same dual row connector on the back:

Here is a “fuzzy” picture of the two boards side by side:

The USB connector is micro-usb, which I think is more available. There is a micro-sd card slot and a plethora of expansion ports for future extensions like LCD panel, WiFi module or even more extruders.

I also added some SPI EEPROM so we can save settings etc. Last but not least there is a power supply module which provides 5V up to 3A from 12 to 24V input. The 5V and 3.3V from the CPU board are connected to the motor controller board so there is no need for an external 5V buck converter anymore.

The only slight disadvantage is that now I have to use external ST-LINK adapter to program the board and an external serial-to-usb adapter for debugging.

Here is a little video comparing the two boards side by side: