Looking at the differences between the red board and the blue boards ...
The red board:
Good things about the red board:
- 1.5k pull up resistor on the PA12 pin (USB D+) which you can programatically drag down for automated USB reset.
- large power capacitors and LDO power (AMS1117 3.3v).
Problems with the red board:
- Silk screen is barely readable, the text is chopped off on some of the pins
- USB connector only has two anchor points and it is directly soldered on the surface
- Small reset button with hardly any resistance
The blue board:
Good things about the blue board:
- Four soldered anchor point on the USB connector. What you can't tell from this picture is that there is a notch in the pcb board and the USB connector sits down inside it some. This provides some lateral stability that takes some of the stress off the solder points. +2
(Actually there are now blue pills that have a two anchor point usb connector)
- It has nice clear readable silkscreen printing. +1
- It also a larger reset button.+1
- Often supplied with a 300mV regulator (rt9193-33gb)
Problems with the blue board:
- Probably won't work as a USB device if it has a 10k or 4k7 pull-up on PA12. You have to check the pull up on PA12 (USB D+). If it has a 10k or 4k7 pull-up resistor, you will need to replace it with a 1k5 one to use the native USB.
Nice features common to both:
- SWD pins broken out and easily connected (VCC, GND, SWDIO, SWCLK)
- USB 5V is broken out with easy access.
- User LED on PC13
- Power LED
- You can probably use more flash (128k) than officially documented for the chip (stm32f103c8t6 64k), I was able to load 115k of flash on mine and it seemed to work.
- Both boards have the same pinouts, you can use them interchangeably
Problems with both boards:
- No preloaded maple bootloader * to me this isn't really a problem as the entire 64k of flash is available for use. Also, every chip provides a factory ROM based serial boot.
- No user button
If people have any more comparisons or comments, please post on this thread.
Another style BluePill (note: pinouts valid for both Red and Blue boards)
http://reblag.dk/wordpress/wp-content/u ... iagram.pdf