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Why Are All These Resistors Thru-Hole? Isn’t SMD Cooler?

SMD is cooler….when a machine does all the work. At the prototyping phase (and assuming you don’t have all the fancier tools specific to the tiny world of SMD), SMD parts take longer to solder, often require a heat gun to remove, and offer no convenient place to hook your oscilloscope probe to. Bodge wires with any hint of durability are much more difficult and time-consuming in SMD land. In short, compared to thru-hole resistors, SMD resistors are a total pain if a person is engaged in an epic battle. If your battle isn’t all that epic, it won’t matter, but who the hell meddles with non-epic battles?

I learned this the hard way in my senior Capstone project back in engineering school. I had a 100mm x 100mm PCB board with a gigazillion components on it. We used a simple voltage divider before an op-amp to scale our voltage for reading with an ADC. All I had to do was swap out 2 resistors to accommodate us moving up to a much larger voltage. This is something that would have taken me 1-2 minutes if I had all the right tools and 2-3 minutes almost the right tools with thru-hole. My school wasn’t equipped for SMD parts. I had to bring in my heat gun from home. Because the board layout was so tight, even with plenty of Kapton tape to protect the good components, I ended up blowing off 4 or 5 extra components off the board. (I was in a rush. That didn’t help.) Of course, these were specific SMD components and I was crawling around the floor looking for them. In the end, the whole mess could have been avoided if I had just used thru-hole resistors.

Obviously, most of the best chips these days are SMD and many of them offer no DIP-style thru-hole option. In those cases, I’ll gladly use the SMD chip and then break it out with 2.54mm header pins and such to allow for maximum protectivity in battle.

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Serial USARTs On STM32 Blue Pill With Arduino Code in PlatformIO

Here’s the “Hello World” edition of getting access to USART2 and USART3 on an STM32 Blue Pill in PlatformIO using the Arduino framework.


/* lib_deps = NONE
  # Using a library name

-------- Platform.ini Settings----------
[env:bluepill_f103c8]
platform = ststm32
board = bluepill_f103c8
#board = bluepill_f103c8
framework = arduino
upload_protocol = stlink
lib_compat_mode = soft

*/

#include "Arduino.h"
HardwareSerial Serial2(USART2);   // PA3  (RX)  PA2  (TX)
HardwareSerial Serial3(USART3); // PB11 (RX)  PB10   (TX)

void setup() {
Serial.begin(19200);   // PA10  (RX) PA9 (TX) 
Serial2.begin(19200);  // PA3  (RX)  PA2  (TX)
Serial3.begin(19200);  // PB11 (RX)  PB10   (TX)

Serial.println("Serial: 1");
Serial2.println("Serial2: 2");
Serial3.println("Serial3: 3");
}

void loop() {
Serial.println("Serial: 1");
Serial2.println("Serial2: 2");
Serial3.println("Serial3: 3");
delay(1000);
}
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STM32 Blue Pill ADC Values Too Low in PlatformIO

 

I kept getting values that were way too low when feeding an ADC on the STM32 Blue Pill 3.3V. I should have been getting values that were around 4000 and instead I was closer to 800.

Solution
1) The default ADC in the Arduino library is set to 10-bit resolution. This is what you normally get with analogRead(). To change it, put this in your setup(). Read more about it here: https://www.arduino.cc/reference/en/language/functions/zero-due-mkr-family/analogreadresolution/

analogReadResolution(12);

Notes
— This would have been a much easier problem to solve if i had been getting values of around 1000. It turns out that my ADC pin wasn’t getting exactly 3.3V. There was a voltage drop in my system – I’ve got a huge mess currently hooked to the Blue Pill – that knocked it down to around 3V. Normally, calculating bit resolution in decimal is 2^x – 1. So 2^10 – 1 = 1023.

— PlatformIO had nothing to do with the error. I’m new to PlatformIO and never know if my issues are due to the STM32’s specific needs, the Arduino library, or some kind of PlatformIO specific issue. It seems that as long as the hardware is setup correctly and
#include <Arduino.h>
is at the top of the program/sketch/whatever, PlatformIO has no ill effects. The problems I have had aren’t the fault of PlatformIO but from adapting libraries intended for AVR to STM32F1.

 

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Genuine STM32 Blue Pill vs CS32F103C8T6 Clone

I’m troubleshooting a synth design and looking at the data on the SPI bus.  I have 10 STM32 clones (CS32F103C8T6) of the STM32F103C8T6 around and decided to try them out since they have the correct USB resistor.

I was getting the following error in PlatformIO.

Warn : UNEXPECTED idcode: 0x2ba01477

To get the clone to work, I had to change stm32f1x.cfg which I found in C:\Users\YOUR_WINDOWS_USER\.platformio\packages\tool-openocd\scripts\target\

I changed set _CPUTAPID 0x1ba01477 to set _CPUTAPID 0x2ba01477.  If I need to go back to the real Blue Pill, I’ll have to change this back again.

I started with the clone and then switched to the real one.  The scope shows some interesting results.  This is data from the SPI bus.  The circuit is 100% identical in both cases.

CS32F103C8T6 Clone SPI Data

Genuine STM32F103C8T6 SPI Data

I’m not sure if the clone just can’t handle the speed or if there’s some kind capacitance slowing it down.  Regardless, the SPI output of the clone is so bad that I’ll have to check the timing diagrams for my SPI-receiving chip.  I don’t have this problem with the genuine STM32.

If anyone knows a solution to get the clone to behave, please tell me.  Otherwise, I’ll have to view these Chinese clones as WAY too expensive once time is factored in.

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bCNC Safe Z

bCNC comes with a feature to move the spindle up to a safe z height.  If you right-click on the “Safe Z” button it looks like this.

G90 G0Z(safe)

The default is 3.  In my case, it was 3 millimeters.  I wouldn’t call that safe at all.  I use clamps that are much thicker/taller than 3mm and most have bolts that stick up closer to 75mm.  I had big trouble figuring how to change the definition of Z(safe).  More importantly, I didn’t like the G90 in the code above.  G90 relies on my working coordinate system.  In my mind, the Safe Z should take the spindle as far up as possible.  This happens to be an absolute positioning thing.  I’ll back off 5mm just to be safe.

I entered this code in the Safe Z window

G53 G0 Z-5

It should look like this.

Now when I press Z, no matter how stupidly I’ve set the working Z0 coordinate, I know the spindle will raise up to it’s maximum (almost).

  • I use a homing cycle.
  • I’m using mm for my units.

Adjust accordingly.