【DigiKey Creative Contest】Multi-channel Micro Gas Chromatography Acquisition Unit-2. Hardware Design

sunduoze

【DigiKey Creative Contest】Multi-channel Micro Gas Chromatography Acquisition Unit-2. Hardware Design [Copy link]

 

3 Hardware Design

3.1 Main Hardware Components

3.1.1 Controller and communication unit

ESP32 is a low-cost, high-performance microcontroller chip developed by Espressif Systems, mainly used in Internet of Things (IoT) applications. ESP32 inherits the characteristics of its predecessor ESP8266 and improves on performance, power consumption and functionality. Here are some important features and introductions of ESP32:

1. Dual-core processor: ESP32 is equipped with two processor cores, which can be used for application processing and Wi-Fi network protocol stack management respectively, improving the overall performance and response speed of the system.
2. Wi-Fi and Bluetooth connectivity: ESP32 supports 2.4GHz Wi-Fi connectivity, which is suitable for wireless network communications. In addition, it also integrates Bluetooth 4.2/5.0 technology, which can be used to connect to other Bluetooth devices or implement Bluetooth Mesh networks.
3. Rich interfaces: ESP32 provides a variety of general-purpose input and output interfaces (GPIO), SPI, I2C, UART, etc., making it easy to connect with other hardware devices and sensors to meet the needs of various application scenarios.
4. Low-power design: ESP32 is designed with power optimization in mind and supports multiple low-power modes, enabling long-term operation in battery-powered applications.

1. ADC Analog-to-Digital Converter

The system uses ADI's EVAL-AD7606CFMCZ evaluation board to implement the ADC function. The AD7606C-18 is an 18-bit, 1 MSPS SAR-ADC (all channels) with an input buffer with a minimum analog input impedance (RIN) of 1MΩ, which can eliminate the previous front-end circuit design and greatly facilitate the collection of parallel data. At the same time, the ADC mode (differential, single-ended) and range can be switched through register configuration, which greatly simplifies the Front-End design cost and simplifies the complexity of system design.

This design uses single-wire SPI to communicate with it to save pin usage (it is not actually necessary, and the communication rate will be limited)

In addition, the evaluation board integrates the ADR4525 Class B reference source with a temperature drift performance of 2 ppm/°C.

The low frequency output noise of 1.25μV pp greatly reduces the overall system error and noise.

Since the chip has 8-channel acquisition function, in order to fully utilize its channels, in addition to the detector signal, auxiliary voltage and current measurement functions are reserved, and the system has different detector power supply voltage monitoring functions. The following is the actual channel configuration information:

Evaluation board jumper cap configuration:

3.1.3 USB to Serial (One-click burning of ESPxx without external transistors)

CH343 is a USB bus adapter chip, which realizes USB to high-speed asynchronous serial port, supports automatic identification and dynamic adaptation of communication baud rate of 115200bps and below, and provides common MODEM communication signals, which are used to expand asynchronous serial port for computer, or upgrade ordinary serial port equipment or MCU directly to USB bus. Through RTS pin and DTRTNOW pin, ESPxx's EN pin and IO00 pin are connected, and flow control is used to realize automatic burning of program.

3.1.4 Other peripherals

1. OLED
   This system uses OLED (SSD1306) as an auxiliary display screen to facilitate user function switching
   
2. Spiral coding button, which is used to interact with OLED UI, greatly facilitating debugging and use

3.2 Power Supply Design

3.2.1 Power Requirements

• The DID & PID in the system require a power supply of 5.6V or above, and the AD7606C EVAL board also requires a power supply of 5V or above.
• The TCD detector requires an 18-20V power supply.
• MCU, OLED and other peripherals all require 3.3V power supply

3.2.2 Power Management

The system uses the Type-C interface and the PD protocol to communicate with the adapter through the cc line, outputting 20V voltage to power the entire system. The buck circuit is used to step down the voltage to 5.6V to power the DID and PID detectors and the AD7606C EVAL board; the ultra-low noise and ultra-high PSRR LDO and programmable resistors are used to generate 18-20V programmable voltage output; the LDO is used to convert 5.6V to 3.3V to power the MCU and peripherals.

1. TYPE-C and PD
   This system uses FUSB302B to achieve USB Type-C detection, including connection and orientation, with less programming. The design can achieve power delivery of up to 60 W.
   
2. Adjustable power supply for TCD
   This power supply uses ADI's LT3045 ultra-low noise and PSRR LDO to provide power to the detector. Due to actual needs (the design here exceeds its typical value but does not exceed its absolute maximum value), it is required to have a small range of voltage regulation function, so AD5272 is used to adjust the maximum voltage (maximum 20kOhm)
   
3. 20V to 5.6V Buck circuit and 5.6V to 3.3V LDO

3.2.3 Current acquisition (measurement range: 0.1A – 9.8A)

The current acquisition part uses the INA290A3 current monitoring amplifier that supports high common-mode voltage. The voltage across the Vishay Y14730R00500B0R ±5ppm/°C 5 mOhms ±0.1% 3W precision resistor is amplified 100 times and sent to ADC-CH8 for acquisition (here the universal interface of ADI's op amp evaluation board is used to connect to the ADC board). Theoretically, a minimum resolution of 76.3uA can be achieved (the actual design connector pin1 does not correspond to pin1 of the ADI board, and ADC-CH8 should be configured for 0-5V unipolar sampling to achieve a current resolution of ~38uA).

3.3 Physical Design

3.3.1 Internal Connections

In order to facilitate the use of boards and repeated development, the board stacking method is adopted. The actual connection is achieved using SMB connectors, plug-in connectors and cables, pin headers and female headers.

3.3.2 External Interface

PID and DID both use Type-C interface (no foolproofing here, but the PD adapter will not be damaged when inserted), and TCD is connected with XH-2.54 connector. In order to facilitate the use of boards and repeated development, the board stacking method is adopted. The actual connection is achieved using SMB connectors, plug-in connectors and cables, pin headers and female headers.

3.3.3 Others

【DigiKey Creative Contest】Multi-channel Micro Gas Chromatography Acquisition Unit-1. Introduction and System Solution

lugl4313820

In order to facilitate the use of boards and repeated development, the board stacking method is adopted. The actual connection is achieved using SMB connectors, plug-in connectors and cables, pin headers and female headers.

Looks very neat!

秦天qintian0303

The DuPont line is used for functional verification, the adapter board is used for prototype testing, and finally the finished board is designed.

sunduoze

Qintianqintian0303 posted on 2024-1-5 14:58 Dupont line connection for functional verification, adapter board connection for prototype testing, and finally the design of the board product

Hahahaha, this is basically the idea.