STM32F411CEU6+ESP8266 dual-purpose board

3D rendering:

Physical map:

ps: The photo quality is really not that good. The real thing is really more beautiful than this photo. Please refer to the 3D rendering.

Peripherals:

1. The onboard CH340 can either download programs to 8266 or serve as a serial port for STM32. The directly connected serial port 1, that is, PA9 and PA10, can be selected through a jumper cap to be used as STM32 serial port output or 8266 automatic download.
2. The board has a 128Mbit SPI flash, CS-PA4, MISO-PB4, SCK-PA5, MOSI-PA7.
3. The high-speed crystal oscillator is 25MHz, the low-speed crystal oscillator is 32.768k
4. Insert all the jumper caps to the left for 8266 to download the program, and insert them all to the right: 8266 is connected to the serial port 2 of the STM32, and CH340 is connected to the serial port 1 of the STM32.

Devices and packages:

1. All capacitors, resistors and LEDs on the board are packaged in 0603, which requires manual patching.
2. The package of STM32F411CEU6 is QFN48, and the pad is stretched by 0.4mm for the convenience of manual patching.
3. Only the bottom of the antenna of ESP12F is not covered with copper, and the board is not cut. It is actually proved to be unnecessary. It is mainly for development purposes and the signal will not be particularly weak.
4. In 2021, there should be no one using Microusb, so I switched to TYPE-C, mainly because it is really difficult to find Microusb.

Pin:

1. All the basic pins of F411 are lead out, (except for PC14 and PC15) and an external low-speed crystal oscillator is connected. Most people really don’t use these two pins.
2. In order to facilitate wiring, the onboard programmable LED pins were changed from the commonly used PC13 to PA12, mainly because the layout was convenient at that time.
3. Not all pins of ESP8266 are lead out. According to the official documentation, the pins that can be used are lead out. The specific pins are (GPIO4, GPIO5, GPIO12, GPIO13, GPIO14, GPIO16, ADC)

Replenish:

1. I have always had a question about the automatic download part of ESP12F. I looked at some nodemcu schematics. Some of them connect DTR to the EN pin, and some of them connect DTR to the RST pin. I don’t know what to say in between. I don’t know, Arduino’s automatic download requires the development board to be set to nodemcu, otherwise the automatic download will not be successful, and the first download may also be unsuccessful, so I added a button to the GPIO0 pin, just like nodemcu. After my testing, After downloading it manually once, it can be downloaded automatically. I have seen many open source projects that have not mentioned this. Newcomers like us can easily suspect that it is a problem with the circuit design.
2. Regarding the question of why jumper caps are used, I have looked for an alternative before, which is to use DIP switches. I also made a board to verify and found that the effect is not particularly good, because I chose a 1.27 pitch DIP switch. Although the code switch occupies a smaller volume, it is not convenient to use every tweezers or pen on hand. Flying lead pads are even more inconvenient.
3. Friends who are planning projects may encounter a problem, that is, the program cannot be downloaded. I have encountered this before, and I once suspected that it was a problem with the circuit design. In fact, other programs were written into the F411 chip I bought. Moreover, the external crystal oscillator used in the previous program is not 25MHz, which will cause the chip to lock up. The solution is actually very simple. First download a flyMCU, and then perform the following steps: power off -> press and hold the BOOT0 button on the board before powering on -> power on -> open flyMCU -> click on the search serial port on the toolbar, and select the serial port connected to the development board , the default baud rate is 115200 -> click to clear the chip. Then you can happily program.
4. Regarding the question of why STMF411CEU6 was chosen, the main reason is that this chip is particularly cheap. Now c8t6 is almost three digits, and it is still so strong. Secondly, none of the F103 series can beat it, but among this chip So there is a reason why it is so cheap. If you are using DWT_CYCCNT for precise delay, don’t use it. This is what ucOS uses. The DWT_CYCCNT of STM32F411CEU6 is very unstable and basically cannot be used. If you don’t use DWT_CYCCNT, it doesn’t matter. . 100MHz main frequency, program storage: 512kB, SRAM: 128kB, except that there are relatively few routines, it is way ahead of STM32F103C8T6.

Light a lamp: