I. Design Background
An ADC (Analog-to-Digital Converter) is an indispensable key component in electronic systems. It converts continuous analog signals into digital signals, enabling digital processing and analysis. ADCs play a crucial role in signal conversion, measurement and data acquisition, control system input, and communication and signal processing. Their widespread application promotes the intelligent and precise control of electronic equipment across various industries, and is one of the key factors driving modern technological progress. Digital voltmeters and ammeters combine ADC technology with circuit measurement principles, accurately converting analog voltage and current signals into digital displays for easy reading and analysis by electronic engineers. This device not only improves the accuracy and efficiency of circuit measurements but also helps engineers better understand circuit behavior, serving as a powerful assistant in electronic design and troubleshooting, and playing a vital supporting role in the work of electronic engineers. In product applications, digital voltmeters ensure the accuracy and safety of circuit design, while also providing strong support for product quality control and subsequent maintenance. Learning to design and build a digital voltmeter and ammeter
using a benchtop digital multimeter (Agilent 34401A)
is highly beneficial for improving one's professional skills. This digital voltmeter and ammeter project covers multiple aspects, including microcontroller circuit design and implementation, signal acquisition and processing circuit design, user interface development and optimization, and product appearance design. It integrates knowledge from multiple fields such as electronics, microcontroller programming, circuit design, and industrial design. Considering the learning pace and knowledge absorption capacity of beginners, we have specially launched this introductory-level digital voltmeter and ammeter project, which is very suitable for beginners in electronics and those who want to learn more about microcontroller applications. This project has the following highlights:
it adopts a core board plus expansion board design concept and uses plug-in components, making learning simpler and exploration more in-depth;
the core board uses the domestic Wuhan Xinyuan Semiconductor CW32 as the main controller, while also being compatible with other similar development boards; however, the CW32 has advantages.
The project is highly comprehensive and practical, and after completion, it can be used as a desktop instrument;
the project has abundant learning materials, including circuit design tutorials, PCB design, code programming learning, and training for engineers' debugging skills.
II. Hardware Design
1. Power Supply Circuit
LDO (Low Dropout Linear Regulator) Selection This project uses an LDO as the power supply. Considering that most voltmeter products are used in industrial scenarios with 24V or 36V power supplies, the SE8550K2 with a maximum input voltage of up to 40V was selected as the power supply. The main reason for not using a DC-DC step-down circuit to handle the large voltage drop is to avoid introducing DC-DC ripple interference during the design process, and the secondary reason is to reduce project costs.
2. MCU Selection Analysis
To reduce the learning cost for everyone, this project uses the LCSC CW32F030C8Tx development board (core board) as the main controller, but this does not mean that we will talk less about this section. From the perspective of training engineers, the correct selection of the main controller is very important, as it relates to the overall advantage of the project. Regarding the voltmeter and current meter, the author used STM32/CW32 and some other 32-bit microcontrollers for some debugging and testing. This comparison is only with the STM32F103C8T6 as a reference for device selection, primarily aimed at providing ideas and improving understanding.
Avoid blind selection. When selecting an MCU (Microcontroller Unit) for this project, multiple aspects need to be considered to ensure the chosen MCU meets project requirements.
Clearly define your project needs: Understand the required computing power, including clock speed, processor core type, and whether a floating-point unit is needed.
Identify the required I/O ports and important peripherals, such as ADC peripherals. Since this is a development board project, primarily for debugging and learning, there are no strict limitations on the number of I/O ports: i.e., the associated costs are not considered.
Key advantages of the CW32 in this project
: Wide operating temperature range: -40~105℃;
Wide operating voltage range: 1.65V~5.5V (STM32 only supports 3.3V systems)
; Superior interference immunity: HBM ESD 8KV; All ESD reliability meets the highest international standard (STM32 ESD 2KV)
; Project focus - Better ADC: 12-bit high-speed ADC, achieving ±1.0LSB INL 11.3ENOB; Multiple Vref reference voltages... (STM32 only supports VDD=Vref);
Stable and reliable eFLASH technology.
A detailed explanation of these advantages will be provided in the chapters on ADC sampling and related extensions.
The main characteristics of the CW32 ADC: This project requires a focus on the 4 reference voltage sources. (Content from the "CW32x030 User Manual")
3. Voltage Sampling Circuit:
The voltage divider resistors in this project are designed to be 220K+10K, therefore the voltage division ratio is 22:1 (ADC_IN11).
The voltage divider resistor selection
is designed to measure the maximum voltage. For safety reasons, this project uses 30V (the actual maximum display value can be 99.9V or 100V).
The ADC reference voltage is 1.5V in this project, and this reference voltage can be configured through the program.
To reduce the power consumption of the sampling circuit, the low-side resistor (R7) is usually chosen as 10K based on experience.
Then, the high-side resistance of the voltage divider resistor can be calculated using the above parameters.
The required voltage division ratio is calculated, i.e., the ADC reference voltage. The input voltage is designed; using known parameters, 1.5V/30V = 0.05 can be calculated.
The high-side resistance is calculated as the low-side resistance/voltage division ratio; using known parameters, 10K/0.05 = 200K can be calculated.
A standard resistor is selected: a resistor slightly higher than the calculated value of 200K is chosen. We usually choose E24 series resistors; therefore, in this project, 220K, which is greater than 200K and closest to the calculated value, is selected.
If, in actual use, the voltage to be measured is lower than 2/3 of the module's design voltage (66V), the voltage divider resistor can be replaced and the program modified to improve measurement accuracy. The following example illustrates this:
Assuming the measured voltage is no higher than 24V and other parameters remain unchanged,
calculations show 1.5V/24V = 0.0625, 10K/0.0625 = 160K. 160K is a standard E24 resistor and can be directly selected, or a higher value 180K can be chosen with some redundancy.
If, in actual use, the voltage to be measured is higher than the module's 99V design voltage, a different resistor can be selected. To expand the voltage measurement range, you can choose to replace the voltage divider resistor or modify the reference voltage. The following example illustrates this:
Assuming the measured voltage is 160V, we can choose to increase the voltage reference to expand the range.
Given that the voltage division ratio of the selected resistor is 0.0145, we can calculate 160V * 0.0145 = 2.32V using the formula. Therefore, we can choose a 2.5V voltage reference to expand the range (increasing the range will reduce accuracy).
Considering the potential fluctuations in the measured power supply, a 10nF filter capacitor is connected in parallel with the low-side voltage divider resistor in the circuit design to improve measurement stability.
(Range switching )
In this project, an additional voltage sampling circuit was added. Therefore, we can discuss the significance of range switching for improving measurement accuracy. Multimeters often have multiple range settings to achieve more accurate measurements. By adjusting different ranges, the optimal measurement accuracy of the measured point within the corresponding range can be obtained.
This project requires a combination of hardware and software to implement this function. When we first use the ADC_IN11 channel mentioned earlier to measure voltages below 30V, if the measured voltage is within 0~3V, then we use the ADC_IN9 channel for measurement. At this time, due to the reduced voltage division ratio, the measurement accuracy is greatly improved. There are many ways to implement range switching; the development board design provides more design possibilities.
4. Current Sampling Circuit
This project uses a low-side current sampling circuit for current detection. When learning the common ground between the low-side of the sampling circuit and the development board's meter interface, please do not solder R0!!!
The design analysis
for this project involves a sampling current of 3A, and the selected sampling resistor (R0) is 100mΩ. The selection of the sampling resistor mainly needs to consider the following aspects:
the maximum value of the pre-designed measurement current;
the voltage difference caused by the 3A current sensing resistor in this project; and
the power dissipation of the current sensing resistor, which should generally not exceed 0.5V. A suitable package should be selected based on this parameter. Considering the power dissipation (temperature) issue under high current, a 1W metal wire-wound resistor package was chosen
. The voltage amplification factor across the current sensing resistor is also important. Since no operational amplifier is used to build the amplification circuit in this project, the factor is 1.
The current sensing resistor value can then be calculated using the above parameters
. Since no amplifier circuit is used, a larger sampling resistor is needed to obtain a higher measured voltage for measurement.
Considering that a larger resistor would result in a larger voltage drop and higher power consumption, an unlimited selection of a larger resistor is not feasible.
This project uses a 1W package resistor, corresponding to a power consumption of 1W.
Based on the above data, a 100mΩ current sensing resistor was selected. According to the formula, 3A * 100mΩ = 300mV, 900mW can be calculated.
To cope with different operating environments, especially high-current scenarios, the R0 resistor can be replaced with constantan wire or a shunt. The replacement can be selected according to the actual application scenario. For safety and educational purposes, this project will not discuss measurements exceeding 3A in detail, but the principle is the same.
5. Digital Tube Display
This project uses a digital tube as the display unit.
This project uses two 0.28-inch three-digit common-cathode LED displays as the display device. Compared to a display screen, LED displays offer better visibility in complex environments. The brightness of the LED displays can be increased by using smaller current-limiting resistors, depending on the specific needs of the application environment. Furthermore, LED displays have better mechanical properties and are not as easily damaged by external forces as display screens. They are widely used in industrial applications where stability and reliability are crucial. From a development board learning perspective, this makes it easier to learn electronic measurement principles and related development in a targeted manner.
In this project, actual testing showed that the current-limiting resistors (R1~R6) for the LED displays were configured to 300Ω. The corresponding brightness for both red and blue LED displays was good and the brightness was soft and not glaring.
Strictly speaking, the current-limiting resistors should be added to the segments; adding them to the digits would affect the display effect. Our actual design places them in the digits to save a few resistors, but the impact on the display is not significant. Therefore, we add them to the digits for convenience.
The
driving principle of LED displays mainly involves controlling the switching state of each segment of the LED display to display numbers, letters, or symbols. The following is a detailed explanation of the driving principle:
Basic Structure of a Digital Tube:
A digital tube typically consists of seven or eight LED segments (eight segments in this project). Each segment represents a part of the digital tube and can display numbers 0-9, letters AF, etc.
Digital tubes come in two types: common cathode and common anode. The difference lies in whether the common terminal COM (the end connecting all LEDs) is connected to the negative or positive terminal of the power supply.
Driving Methods:
Segment Selection: The desired number or character is displayed by controlling the on/off state of each segment of the digital tube. Each segment corresponds to a control signal; when the control signal is on, the segment lights up, and vice versa. (a, b, c, d, e, f, g, dp)
Bit Selection: The digital tube to be displayed is selected by controlling the bit lines of the digital tube. Bit line control sets the bit line of the digital tube to be displayed to a high level, and the bit lines of other digital tubes to a low level. By continuously switching the state of the bit lines, the display switching between multiple digital tubes can be achieved.
Driving Circuit:
The driving circuit for a digital tube can be implemented using hardware circuits, such as integrated circuits like digital signal processors (DSPs), microcontrollers (MCUs), or shift registers, to generate control signals suitable for the LEDs.
These control signals can be in the form of pulse width modulation (PWM) signals, serial data signals, etc. By controlling the frequency, width, and amplitude of these signals, the brightness of the digital tube can be controlled, thereby displaying the desired numbers or letters.
Software Control:
In addition to hardware driving circuits, the driving of digital tubes can also be implemented through software control. By programming to generate control signals suitable for the digital tubes, more flexible and complex display effects can be achieved, such as scrolling or alternating display of numbers.
Driving Common Cathode and Common Anode Digital Tubes:
For common cathode digital tubes, the common cathode pin is connected to the negative terminal of the power supply, and the control pin is connected to the output pin of the control chip. When a certain number needs to be displayed, the control chip outputs the corresponding encoded signal to the control pin, causing the corresponding LED segment to light up.
For common anode digital tubes, the working principle is similar to that of common cathode digital tubes, except that the common anode pin is connected to the positive terminal of the power supply, and the control pin is connected to the output pin of the control chip.
Encoded Display:
In order for the digital tube to display the corresponding numbers or characters, the segment data port must output the corresponding character encoding. For example, to display the number "0", the character code for a common anode seven-segment display is 11000000B (i.e., C0H), while the character code for a common cathode seven-segment display is 00111111B (i.e., 3FH). The specific code depends on the actual seven-segment display.
Dynamic and Static Display:
Seven-segment displays can use either static or dynamic display methods. In static display, each of the eight segments of each seven-segment display is connected to an 8-bit I/O port address. As long as the I/O port outputs a segment code, the corresponding character is displayed and remains unchanged. Dynamic display, on the other hand, lights up each segment of the seven-segment display one by one, achieving simultaneous visual display through rapid switching.
In summary, the driving principle of seven-segment displays is to control the switching state of each segment of the seven-segment display to display numbers, letters, or symbols, and to achieve display switching between multiple seven-segment displays through segment selection and digit selection. Furthermore, the driving of seven-segment displays can be implemented through hardware circuits or software control, and common cathode or common anode seven-segment displays can be selected as needed.
This project actually uses dynamic scanning display to drive the seven-segment display.
To estimate the current required for the digital tube display,
this project actually uses dynamic scanning to drive the digital tubes. Therefore, at any given time, only a maximum of 8 segments of the digital tube (or LEDs) can be lit, or in other words, only one digit can be lit. According to the design, the required driving current is approximately 11mA, which is the high-level voltage of the I/O port: 3.3V ÷ 300Ω.
At this point, it is important to ensure that the selected MCU has sufficient current-source/current-sinking capability.
Analysis of the datasheet shows that the CW32 has no issues. (Some chips do not work.)
6. LED Indicators
This project additionally designed a power indicator and an I/O operation indicator.
LD_PWR is the power operation indicator
. Since the chip's I/O often has a greater current sinking capability than a current pulling capability, LED1 is designed to be active low (on).
To reduce the current consumption of the LED, some LED brightness is sacrificed, the number of component parameters is reduced, and the current-limiting resistor for the LED is selected as 10K.
7. Button Circuit Design
There are various design methods for the button control circuit. Thanks to the fact that the CW32's I/O port can be configured with pull-up and pull-down resistors internally, the button control circuit on the outside of the chip does not need to be configured. One end of the button is connected to the MCU's I/O, and the other end is grounded. When the button is pressed, the I/O is pulled low.
8. TL431 Circuit Design for Voltage Measurement and Calibration:
This project adds an extra TL431 circuit to provide a 2.5V reference voltage. This can be used to provide an external voltage reference for the chip to calibrate the AD converter. From a product design perspective, due to the inherent ADC performance advantages of the CW32, this circuit is not necessary. This circuit is designed on the development board to learn the relevant application principles.
The TL431 is a relatively "old" device, a classic, and widely used one, still found in many electronic products.
Many beginners may be encountering this device for the first time, so we will briefly explain its principles to help everyone better apply the TL431.
TI defines it as a "Precision Programmable Reference." On the first page of the references, we can focus on several key characteristics.
Precision: Precision indicates that its output voltage is very accurate. I used a ±0.5% accuracy TL431, which measured 2.495V on the board at room temperature. Compared to common Zener diodes, the accuracy is vastly different. In the application circuit diagram, the TL431 is represented by a Zener diode symbol.
Adjustable Output Voltage: The adjustable output voltage is between Vref and 36V. In our project, we use the output Vref voltage, which is approximately 2.5V. Therefore, we use 2.5V in the description, which is approximately equal to Vref.
Sinking Current Capability: This refers to how much current the output voltage pin can provide. This is greatly influenced by the resistance value (R13) in the application circuit. It should not be less than 1mA. If there is no need for sinking current, do not design the current to be too high, as this will cause unnecessary power consumption.
Project Introduction
: This is a color silkscreened expansion dock
project. Features:
4-port USB hub, providing four USB 2.0 downstream ports, backward compatible with USB 1.1 protocol specifications,
supporting high-performance MTT mode, providing an independent TT for each port to achieve full-bandwidth concurrent transmission, with a total bandwidth four times that of STT.
DC input port, eliminating worries about insufficient power supply from the computer's built-in USB ports.
Maximum 3A output current, even for charging (when using the DC interface).
Project Parameters:
USB HUB controller chip uses CH334
synchronous buck converter; TPS563201, 3A output current, compact and powerful,
providing one DC007 and one Type-C power port, one USB-C upstream port, and four USB-A downstream ports.
[Image of the actual product]
CH334DS1.PDF
tps563201.pdf
2024-10-19 16-12-43.mp4
PDF_[Color Silkscreen] USB-HUB Based on CH334P.zip
Altium_[Color Silkscreen] USB-HUB Based on CH334P.zip
PADS_[Color Silkscreen] USB-HUB Based on CH334P.zip
BOM_[Color Silkscreen] USB-HUB Based on CH334P.xlsx
91559
The smallest Daplink ever - with 485 communication
This project is an extension of the open-source mini daplink V2 project by Xifan Fangjiang. The Kicad project has been ported and adapted to JLC, and the TTL serial communication has been changed to the 485 communication mode. Thanks to Xifan Fangjiang for his selfless open-source spirit.
Project Overview:
This project is a modified version of Daplink V2 by the developer "Xifan Fangjiang". While retaining the original mini size design, it adds a 485 communication circuit, facilitating debugging and testing in fields such as industrial automation and manufacturing. Its size is only about the size of a USB-A cable (roughly the size of the top of a data cable). If you do not require 485 communication, you can try to understand, learn, and replicate Xifan Fangjiang's original project, which is attached.
ARM official DAPLink project address: https://github.com/ARMmbed/DAPLink
Heze official DAPLink project address: https://gitee.com/hanszeng/daplink
Project features:
Supports SW mode debugging and downloading, supports 485 communication; --241019
Theoretically, this design is compatible with four types of downloaders. ST-Link and DAPLink have been tested; only the relevant firmware needs to be flashed. --241019
Notes:
The main controller can use multiple series of F103 models. Different models require different firmware flashing. If you are capable of compiling the project yourself, you can use the official ARM project for modification. --241019
The ST-Link firmware does not have onboard LED drivers, so the LEDs will not light up when using ST-Link. An upgrade is required after flashing the ST-Link firmware; the specific method will be mentioned later. --241019 The
ST-Link firmware has a virtual USB drive, but no virtual serial port. This means you can use it as a downloader and download via virtual USB drive, but it cannot be used as a serial port. This issue is currently unresolved; perhaps a more advanced firmware is needed? —241019
J-Link theoretically supports this, so I suggest everyone give it a try. Feel free to add your suggestions in the comments section and contribute to the open-source community. —241019
The pinout in this version is rather messy, as required by my project. If you find it unsuitable or inconvenient, please feel free to modify it further, but remember to open-source it so everyone can learn from it. —241019
Different downloader firmwares have inconsistent support for chips with different kernels. Pay attention to the firmware's applicability and flash it according to your own needs.
Possible problems and solutions:
For some flashing steps and firmware upgrade issues, please refer to this article: https://blog.csdn.net/weixin_42880082/article/details/127293349
St.'s official ST-Link upgrade guide: https://www.st.com/resource/zh/release_note/DM00107009-.pdf
Article on operating the virtual serial port supported by STLink 2.1: https://blog.csdn.net/weixin_42880082/article/details/127963348
For space-saving purposes, the USB interface should be a recessed design. Using other interfaces may lead to incompatibility issues and unstable soldering. However, it's worth trying; you might discover a new idea.
How to use the SW interface to flash firmware into the programmer?
QA: JLink users can use JFlash, STLink users can use STMCUBOPROGRAMER, and DAPLink users can use OpenOCD or PYOCD command lines. Specific operations are not detailed here; please search online.
Sign --DF241019 ----- Recorded on 20241019
Programmer Usage:
The pins on the chip side of the front are used for flashing other chips. A is the A signal in the 485 communication signal pair. Note that the 5V power supply is not isolated; it can power the target via USB, or it can introduce electrical shocks from the target into the USB. This means that introducing high voltage from the pins will damage the USB device! !! Please be extremely careful not to connect the wires incorrectly!!!
It is recommended to use only the dio, clk, and gnd wires for debugging. During debugging, the target board needs to be powered by other components.
The pins on the reverse side of the programmer are for programming the firmware and for the B signal of the 485 communication. Pay attention to the arrow direction and do not connect the wires incorrectly.
For feedback and answers to questions
, please leave a message in the comments section if you encounter any hardware difficulties or questions. The author will try to reply as soon as possible.
STLinkV2.J28.M18.bin
air32_daplink_v2.hex
air32_daplink_v1.hex
air32_daplink_v1_iap.hex
air32_daplink_v2_iap.hex
ARM official DAPLink.zip
Original project DAPLink-V2.zip
PDF_The smallest Daplink in history - with 485 communication.zip
Altium - The smallest Daplink ever - with 485 communication.zip
PADS - The smallest Daplink ever with 485 communication.zip
BOM_The smallest Daplink ever - with 485 communication.xlsx
91560
Replica ESP32-C3-DevKitC-02
Replica Espressif ESP32-C3-DevKitC-02 development board
This is a replica of Espressif's ESP32-C3-DevKitC-02 development board, with dimensions and definitions identical to the original. It also uses a 0603 package for easy manual soldering.
Schematic reference source: [Espressif ESP32-C3-DevKitC-02](https://docs.espressif.com/projects/esp-dev-kits/zh_CN/latest/esp32c3/esp32-c3-devkitc-02/index.html)
![IMG_20241019_145707.jpg]
![IMG_20241019_145613.jpg]
10.28 Update: Fixed a silkscreen error; this does not affect actual use.
VID_20241019_150009.mp4
VID_20241019_154653.mp4
PDF_Replica ESP32-C3-DevKitC-02.zip
Altium_Replica ESP32-C3-DevKitC-02.zip
PADS_Replica ESP32-C3-DevKitC-02.zip
BOM_Replica ESP32-C3-DevKitC-02.xlsx
91561
A step-down module based on TPS5450 to convert 10V~31V to 5V.
The market offers a wide variety of power supply modules, with inconsistent quality and a high failure rate. Therefore, it is necessary to design a suitable DC-DC power supply module.
The TPS5450 is a high-output-current PWM converter integrating a low-resistance, high-side N-channel MOSFET. The board, featuring the listed characteristics, also includes a high-performance voltage error amplifier (providing high regulation accuracy under transient conditions), an undervoltage lockout circuit (to prevent startup before the input voltage reaches 5.5V), an internally integrated slow-start circuit (to limit inrush current), and a voltage feedforward circuit (to improve transient response).
The input voltage range is 10V to 31V,
and the output voltage is 5V.
Using the calculated formula, R1=15.8K and R2=5.1K, the output voltage is made equal to 5V.
Output accuracy: No-load output 5.00%,
Full-load output 4.99%. The
output accuracy meets design requirements
. High-frequency electrolytic capacitors and TVS converters help improve dynamic response.
This buck module's ripple under load is basically within requirements, not exceeding 60mV.
The conversion efficiency fluctuates around 85% at various output currents.
PDF_10V/31V to 5V step-down module based on TPS5450.zip
Altium_10V/31V to 5V step-down module based on TPS5450.zip
PADS_TPS5450-based 10V/31V to 5V step-down module.zip
BOM_Based on TPS5450, implementing a 10V/31V to 5V step-down module.xlsx
91562
ESP32-S2 Development Board
ESP32-S2-WROVER-I Development Board
The ESP32-S2-WROVER-I development board exposes all I/O pins and adds 3x6 WS2812B RGB LEDs.
PDF_ESP32-S2 Development Board.zip
Altium_ESP32-S2 development board.zip
PADS_ESP32-S2 Development Board.zip
BOM_ESP32-S2 Development Board.xlsx
91563
LED light panel
This introductory project helps children become familiar with the use of JLCPCB EDA.
1. Introduction:
Are you ready to begin learning hardware circuits? Hardware learning is inseparable from PCB design, so learning to use JLCPCB EDA for PCB layout is essential. Starting with a simple LED circuit, you will learn some basic usage methods of the JLCPCB EDA editor, PCB circuit design, and PCB board fabrication, etc.
2. Schematic: The schematic
uses three LEDs connected in a common cathode configuration, using a header pin as the power input. When the input is high, the LED conducts. The header pin can be connected to the development board to create an LED running light effect using a microcontroller.
3. PCB and Soldering:
When designing the board outline, you can import DXF files to make the outline more than just a square shape. You can add your favorite silkscreen or images to the board; you can also open windows to make the pattern silver for a more sophisticated look.
Components are very easy to find: three free LEDs, three free resistors, and one header pin. Soldering may be difficult for beginners, but the circuit content is simple and the soldering difficulty is low, making it very suitable for beginners.
dfe3f33b5ee7515da839ce9c896d7903.mp4
c2f80915044043a74ddb40de8d63dab2.mp4
PDF_LED Light Board.zip
Altium_LED Light Board.zip
PADS_LED Light Board.zip
BOM_LED Lighting Panel.xlsx
91564
electronic
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