Upgrade of Environmental Monitoring Instruments

My first open-source project, "Multi-parameter Miniature Environmental Quality Detector Based on ESP07S," received a lot of love and support, garnering 26,000 views in just six months. Many fans offered various suggestions, and many successfully replicated the project and shared
                                                                                                                                                                                                                         
their work in the comments. I'm very happy to see everyone's enthusiasm for this project. One fan in particular, Zhang from Qingdao University of Science and Technology, showed great interest in the project and made some improvements. He actively communicated with me privately, sharing his ideas. With his permission, I rebuilt a professional version of the open-source project and incorporated his improvements into it, sharing it with more embedded development enthusiasts. I thank Zhang again and hope that more like him will join in the future, making this project even more perfect. The main
 
improvements
                                                                                                                                                                                                                         
include: the middle layer control board, the bottom layer power board, the casing, and the assembly method.
 
1. Middle Layer Control Board
: When replicating the original project, Zhang discovered that when using a stencil to apply solder paste and soldering with a heating table, some vias on the middle layer control board PCB were too large to fit solder resist, causing solder paste to leak from the vias during melting, resulting in poor soldering. This is commonly known as "solder leakage." To solve this problem, he improved two versions of my original middle layer control board PCB design. (Version numbers are V1.0 and V1.1). Version V1.0 mainly modified the position and size of various vias. Except for the large-area ground pad and antenna pad, there are no vias on the other pads, which perfectly solves the problem of solder leakage caused by vias in the pads. The component layout and model of version V1.0 are basically the same as the original version. Version V1.1 inherits the fixes of version V1.0 and also optimizes PCB routing, some component layouts, some component packages, and adds reference silkscreen for all components to facilitate the soldering of each component.
 
The PCB plan of the mid-layer control board V1.0 and
the PCB plan of the mid-layer control board V1.1
are shown. Regarding the soldering method for the mid-layer control board, Zhang proposed a new approach: using Sn42Bi57Ag1 low-temperature solder paste with a melting temperature of approximately 148 degrees Celsius. First, solder all components on the front side of the PCB (the side where the ESP07S module is located). Then, apply solder paste to the back side and place all components there. Since the ESP07S module and Type-C interface on the front side of the PCB are at the same height, the soldered PCB can be placed face down on the heating platform for soldering the back side. When removing the PCB after soldering the back side, it must be done carefully and perpendicular to the heating platform. Do not shake it excessively during removal, otherwise components may shift or fall off. This method requires a high degree of precision in the soldering process and necessitates the use of a stencil for solder application. However, the soldering process is simpler and requires fewer tools and equipment. Regarding the control of the heating table temperature during soldering, for Sn42Bi57Ag1 low-temperature solder paste, when soldering the front side of the PCB, first stabilize the heating table temperature at 170 degrees Celsius, then place the PCB on it and solder the front side. Simultaneously, adjust the heating table to 200 degrees Celsius. When it reaches 200 degrees Celsius, remove the circuit board; the front side of the PCB is now soldered. For the back side of the PCB, first stabilize the heating table temperature at 180 degrees Celsius, place the PCB face down on the heating table, and then heat to 220 degrees Celsius until the solder paste on the back of the PCB melts. Then, remove the PCB vertically; the soldering is complete. This soldering method has been tested and, apart from being slightly slower, it generally does not result in component damage.
 
2.
For the bottom power board, Zhang replaced the 5V boost module (finished module) with a 5V boost circuit (onboard circuit), which is more user-friendly for fans who have common resistors and capacitors on hand, and also reduces material costs. The 5V boost circuit uses the SDB628DC-DC boost power chip manufactured by LCSC Semiconductor. The SDB628 integrates an 80mΩ power MOSFET, supports a minimum input voltage of 2V to a maximum of 24V, a fixed switching frequency of 1.2MHz, an internal 4A switching current limit, and a conversion efficiency of up to 97%. The datasheet for this chip can be found by searching for C77805 on the LCSC online store. For the soldering
 
instructions on the bottom control board PCB
, please refer to the soldering guide in "Multi-parameter Miniature Environmental Quality Detector Based on ESP07S". The recommended soldering order is as follows: first, use a heating plate to solder all components on the front of the PCB, then use a soldering iron or hot air gun to solder the two capacitors on the back. Note that if the middle control board is version V1.1, the overall thickness of the middle control board increases because the L2 inductor on the back of the V1.1 middle control board has been changed from a 1206L package to an L0630 package. This requires the battery size on the back of the bottom power board to be modified to 802025 to be compatible with the V1.1 middle control board.
 
3. Shell and Assembly Method:
Zhang improved the front shell of the original shell by optimizing the screen window and buttons, and readjusting the layout of the heat dissipation holes. A recessed groove was added to the screen window area to hold the OLED display in place, which eliminates the need to paste the OLED display. The recessed groove also completely covers the non-displaying part of the OLED display, improving the overall visual experience. The document includes comparison images of
 
the front cover and buttons . The BOM (Revised).xlsx file contains the original sensor cover BOM, the original top-layer 0.96-inch OLED screen BOM, the V1.1 version mid-layer control board BOM, and the revised bottom-layer power board BOM. The V1.0 mid-layer control board has essentially the same components and layout as the original; refer to the BOM (Original).xlsx file. Users of the V1.1 version mid-layer control board should replace the battery on the back of the bottom-layer power board (whether original or revised) with an 802025 battery. The battery connection is the same as the 902025 battery connection in the BOM; simply select the (802025-300mAh) option to purchase. A simulated assembly demonstration video is also included.