This board was partially assembled by JPCPCB, I populated the connectors. I wish I could find some colored 3 pin JST XH connectors for the end stops.
I’ve been busy over the holidays. Here is a summary of the recent progress with the PrntrBoard V2 3D printer controller.
I decided to give the JLCPCB SMT Assembly service a try and ordered some TMC2209 driver boards as well as some semi-assembled PrntrBoard V2 controllers. Overall I was quite happy with the results.
Here is a picture of the driver boards. I tested all of them and they worked flawlessly out of the box.
These are the semi-assembled controllers. I use semi-assembled, because only the SMT components were populated and I have to spin my soldering robot to work on the thru hole connectors.
Next I tested the sensorless homing capability of the TMC2209 drivers. After some tuning of the sensitivity parameter is works very well. You can see one linear rail axis homing with no sensors in this video:
I also decided to work on improving the mounting of the drivers to the board. The driver boards were not very stable in the PCI Express slots and I designed these little plastic holders to fix them in place.
They are bolted to the bottom of the controller PCB. The drivers are very well affixed in place.
While I was trying to get my 2004 LCD panel to work with the controller, I found that not all “standard” EXP1 and EXP2 connectors have the same orientation. At first I though that the SKR 1.3 board, just has them backwards, but I then found this article on the RepRap discussion forum. It appears that the original schematics had an error and now some boards/displays are just backwards. I quickly flipped the connector on my 2004 display and with worked, but this can be quite frustrating.
I made a small PCB that one can use to flip the polarity of the connectors. “To flip or not to flip” seems to be ongoing question.
I tried to do some thermal testing on the TMC2660 drivers. First I tried running my puny motor at 2A with a 60cm 5V fan blowing at the driver. This kept the driver quite cool, which was a not interesting.
I was planning to run all 3 axis at the same time, but my heat sink was just a bit too tall and was touching the other driver :-(. I ordered slightly shorter ones, but they have to swim trough the pacific ocean first.
While I was enjoying torturing the poor motor at it’s rated limit. The thermal camera picked an unusual hot spot on the board. The reverse protection diode was cooking quite a bit. Serves me right for being lazy and not doing the reverse protection the proper way. Even with only one motor running, the diode was dissipating quite a bit of heat. I can’t imagine in what world this part is rated for 10A continuous current. Maybe it needs a small refrigerator attached.
Anyway I changed the schematics to use a proper P-channel MOSFET and a zener.
I added a small cooling pad on the PCB to help the transistor cool off. Hopefully this will not overheat with full 10A load.
I also decided to test one of the last remaining circuits on the board – the servo connectors. This proved to be quite the challenge. There was a serious contention for Timer #7 on the micro controller.
First Marlin’s temperature control was set to use Timer 7. This was not making the Servo module happy. I moved the temperature module to use Timer 8. Then I found that the SoftwareSerial code was also trying to hijack Timer 7. Moved that to Timer 12.
Finally the servo was working properly. I was able to set the position with the M280 command. I decided to quit while I was ahead.
More next week.
I was feeling elated by my success with the FYSETC mini 12864 panel and I tried my old “REPRAP Discount Graphics” panel. I thought “surely this should work as well it’s the same SPI graphics LCD after all”.
We you guessed it – work it did not. I tried software SPI, hardware SPI, nothing. Looks like I had to read the manual. Shame!!!
Here is what I found. The old “discount graphics lcd” is not quite the same chip. It uses ST7920 controller, which is a supreme oddball. It uses some very strange scheme and transfers data 4 bits at a time.
Then I remembered I had added support for hardware SPI for that chip since PrntrBoard V1. Why was it not working?
Well, it was because for some strange reason the data pins on the panel are not connected to the SPI interface on the EXP2 connector, so the u8g library has to use software SPI emulation and I didn’t add support for that.
So fixed that, now I have both hardware support and software emulation for the st7920 driver and here it is working:
Next I’m waiting on some 2004 LCD screens to arrive. These should be easier, since there is no hardware protocol involved.
First my woes with the TMC2209 driver boards are ongoing. The company making the PCBs called that they could not complete my last two prototype designs. The issue was that I didn’t pay attention to the fabrication capabilities and used the wrong design rules.
Long story short I had to re-wire part of the board to meet their spec and submit another order. Alas that meant I have to wait another two weeks for the boards to appear 🙁
In the mean time I was trying to test what I can with the rev1 prototype I had. I tested the heaters and thermistors are working. Now it was turn to my old nemesis – the LCD panel.
The software for these LCD panels is remarkably convoluted and not at all supported on STM32 series of MCUs. I had to write two more drivers for the U8G library, but finally some good progress:
I got the FYSETC mini 12864 panel to work. To finish the week, I also verified the SD-card interface is working.
Here is my first assembled prototype of the V2 board. I only had patience to solder 3 PCIe connectors and skipped on the Thermocouple and servo connectors for now.
Sorry about the “no clean” solder paste gunk around the fuses. I noticed it after I took the picture.
Here is a picture with the driver boards in the slots
And slightly different angle
Here I added a 40x10mm fan for scale comparison
I’m not set on the 40mm fans for cooling, I ordered some 60mm and some 50mm and will do some experimentation what would be the best combination.
Next, I’ll make some driver boards and start porting Marlin to test the contraption.
Many thanks to the awesome team at JLCPCB. I’m really impressed by the speed and the exceptionally low prices. I ordered a set of prototype boards for the V2 design on Oct 28th and they arrived today at my door. Total 8 days including shipping from China.
Here it is 150x105mm 2 layer board:
I ordered the 2660 drivers also from JLC, but I don’t like the red mask color:
The 2660 driver is 4 layer board with “gold fingers” – this is code for the board edge PCIe connector.
The purple board is the 2209 driver. That board is from ohspark. No much difference between the two, except the ENIG finish is standard on oshpark and the purple color is dope. The JLC board comes with a little chamfer around the connector, which is nice.
This is what the driver board looks like plugged in a PCIe slot.
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.
I did some simple thermal tests on the TMC2209 board. In theory these driver chips can supply up to 2A RMS current to the motors. Silent StepSticks with the same drivers are rated around 1.2 to 1.4A depending on the manufacturer.
The test setup
I used all passive cooling. Ambient temperature was 25C. I used a small 9x9x12mm heatsink on top of the driver chip. These are commonly used on the TMC2209 StepStick boards from China (FYSETC or BIGTREETECH). These are not great, but that is what I could fit in the space. I’ll try to move some of the capacitors to make space for a larger heatsink.
On the bottom I used a 20x14x6 heatsink. Not ideal, but that is what I had laying around. There is enough space for a much larger one (25x25x8 for example).
I used a Seek thermal camera “mounted” on a small microscope stand and connected to my old Nexus 5X phone.
First I tested it at 1A RMS current. I use several very slow speed motion commands (G1 Y250 F50 followed by G1 Y0). I found that slow speed motion is much more challenging to the driver heat wise.
After about 20 minutes it board heated to about 47C on the top:
The heatsink was barely warm to the touch. In my experiments the top of the drivers always heats up more than the bottom, probably because of the relatively large thermal mass of the PCB itself.
Next I ran the board at 1.4A RMS. This was more challenging test for the heat dissipation. It took a while for the temperature to stop rising. It stabilized at around 64C on the top:
And around 55C on the bottom:
In the picture the heatsink looks “cool” because the camera can not compensate for the different emissivity of the bare aluminum.
Both top and bottom heatsinks were considerably hot to the touch. Not “burn your fingers” hot, but “I cant keep my fingers longer that 5 seconds” type of hot.
In both cases I did not get any over-temperature warnings from Marlin. I would say 1.4A is the limit on convection heat dissipation of this board in this configuration.
The Seek camera has around +/ – 5C accuracy.
I did one last test at 1.8A RMS. This was on the extreme side of the capabilities of the board. The temperature of the driver kept climbing slowly. Once it reached around 75C on the top I got an overheat alarm in Marlin, so I turned the power off.
I’m confident with some active cooling the driver would be able to run at this setting, because it took quite some time to get to the alarm.