[Complete design] One to four TTL2.0

## Question requirements:

This project is one-to-four TTL designed to facilitate the debugging of smart factory control systems. Its function can be completely independent to realize automatic downloading of two ESP8266 and ESP01 and automatic downloading of two STC microcontrollers or downloading for ARDUINO.

## Question analysis:

Dual TTL download, using the HUB chip, plus four CH340C to realize the data transmission function. At the same time, the author found that D+D- is the prerequisite for the control chip to work very well. For this purpose, the patch switch control module is used to work, and at the same time, it leads to Indicator lights make it easy to observe the current debugging status.

In order to ensure safety, a 3D shell is drawn, which can be prototyped in Jialichuang's 3D Monkey.

Flowchart of the plan

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## Schematic design description

tips: Explain the design schematic diagram of the module in the work. It needs to be accompanied by a schematic diagram, preferably with a physical diagram. Each module needs to be explained. If no design is required, please indicate the source of acquisition.
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This automatic download circuit can realize the automatic reset of the microcontroller when the computer downloads the program. Its working principle is that when data is transmitted, RTS is pulled low for at least 100ms. After power on, +3.3V pulls up the base voltage of Q1 through the R20 resistor. At this time, Q1 is turned on to the ground, and the charge is released after passing through R11. At that time, the gate of U2 is low level, and the R17 resistor is a 10K pull-up resistor. At this time, the U2 gate will not be pulled high, so the U2 gate is low level after power-on, because U2MOS is turned on by the P-channel VGS low level (negative voltage). Vgs=Vg-Vs Because Vg is approximately 0V and Vs is +3.3V, the turn-on condition is reached. At this time, STC_VCC is 3.3V. The microcontroller works normally.

When the computer downloads the program, RTS is pulled low. At this time, the right side of the capacitor C3 is 3.3 high level. The left side is pulled low, so the capacitor is in a "short circuit" state for a moment. When the capacitor is fully charged, it is in a disconnected state. . In the short circuit state, Q1 cannot reach the turn-on voltage. Due to the presence of the R1710K resistor, the collector voltage is high during the charging process of the capacitor, and U2 is cut off. At this time, the STC_VCC voltage is low. When fully charged, Q1 is turned on and U2 When it is turned on, STC_VCC is 3.3V, so C3 uses a 22uf capacitor. The larger the capacitance, the longer the power-down time of the microcontroller. D3 is a voltage stabilizing diode to prevent voltage abnormalities. The resistor of the RTX string is used to achieve impedance matching, and the diode on TXD prevents the CH340C voltage from flowing back and causing the microcontroller to fail to reset normally.

The automatic download circuit is currently used without problems. ![image.png] When ESP32S2 does not have an RST interface, connect EN on the ESP32S2 board to the download circuit.


When the RES pin ESP001SIO0 is grounded, it enters download mode. GPIO0 remains low at the rising edge of EN (also called RST). Ping (this schematic diagram RST and EN are linked together)


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Serial port download indicator

## PCB design instructions

Tip: Write some design instructions for the PCB here, such as: PCB layout, wiring, line width, spacing Other design considerations:
PCB design should consider VCC traces, thicker ones are better.

There was a time when the wires on the 3A circuit board started to smoke, but it didn't burn out.

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This FPC socket, please be sure to pay attention to the order of the lines before using this package and schematic diagram! Don’t let all the dozen or so wires turn upside down! I did the opposite once.

## Software description

tip: The software can be nested using code blocks. There is no need to describe all software parts. Just describe the important parts.
**Code block:**

```
No software description```

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Physical display Description

tips: Actual pictures of the work, and descriptions can be added to the pictures.
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## Precautions

: Here are some precautions that need to be paid attention to in the production of the work (you can omit it if you don’t have it)
FPC seat It is recommended to use solder paste and a hot air gun to solder at a temperature of 230 degrees to 260 degrees. I used a teppanyaki, and the whole dormitory window was directly opened for ventilation. I was almost evicted from the dormitory

## Demo video

tip: Just upload the attachment to the demo video. The attachment can only be long-distance uploaded files of up to 50M. Files larger than 50M can be placed in On other network disks or video websites, just put the address link here

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Tips for uploading other attachments: Works participating in the event must upload project-related program attachments to the open source platform or personal code storage cloud. The maximum attachment support is 50M upload (please do not upload in Lichuang workspace, there are restrictions)