使用惠斯通电桥Wheatstone bridge 搭建柔性电子器件测量平台

安装依赖

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pip install pyvisa
pip install PyVISA-py
pip install pyvisa-py
pip install matplotlib numpy

查看电脑上可使用的端口

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import pyvisa

rm = pyvisa.ResourceManager()

print(rm.list_resources())

示例输出：

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('ASRL/dev/cu.debug-console::INSTR', 'ASRL/dev/cu.MilkyWays::INSTR', 'ASRL/dev/cu.Bluetooth-Incoming-Port::INSTR', 'USB0::1689::874::C101038::0::INSTR')
/Users/lianbin/mambaforge/envs/gpib-waveform/lib/python3.9/site-packages/pyvisa_py/tcpip.py:121: UserWarning: TCPIP::hislip resource discovery requires the zeroconf package to be installed... try 'pip install zeroconf'
  warnings.warn(

控制gui编写，使用Trae，只用了一天完成所有code编写

在这里很多非常精华的点可以记录，找时间整理，收获颇丰

oscilloscope 遇到的问题

– 写入速度很慢，无法及时写入信号，可能直接传入wavform有关系

处理速度优化

示波器传输速率似乎太慢无法满足要求，改用arduino

让我解释一下 Arduino 的参考电压选项：

使用 arduino 作为oscilloscope

(需要添加示意图)

  1. 默认情况（不设置 analogReference）：

    • 使用 5V 作为参考电压
    • ADC 范围：0-1023 对应 0-5V

  2. 使用 EXTERNAL：

    • 需要在 AREF 引脚上提供外部参考电压
    • 如果没有连接，读数会不稳定或保持在最大值

建议修改代码如下：

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const int CHANNELS[] = {A0, A1, A2};  // 模拟输入引脚
const int SAMPLE_INTERVAL = 50;       // 采样间隔(ms)

void setup() {
  Serial.begin(115200);  // 高波特率
  // 使用默认的5V参考电压
}

void loop() {
  for (int i = 0; i < sizeof(CHANNELS)/sizeof(CHANNELS[0]); i++) {
    int value = analogRead(CHANNELS[i]);
    float voltage = value * (5.0 / 1023.0);  // 转换为实际电压值
    Serial.print(voltage, 3);  // 输出3位小数的电压值
    Serial.print(",");
  }
  Serial.println();
  delay(SAMPLE_INTERVAL);
}

主要修改：

  1. 移除了 analogReference(EXTERNAL)

  2. 添加了电压转换计算

  3. 输出实际电压值而不是原始 ADC 值
    如果您之后需要使用外部参考电压，请确保：

  4. 正确连接 AREF 引脚到稳定的参考电压源

  5. 参考电压值不超过 5V

  6. 添加去耦电容到 AREF 引脚

问题总结：

使用低通滤波 (rc low pass) 做信号过滤，选用 4.7kohm R 0.15uF C 来进行设计，截止频率225.75 Hz左右，达到设计要求

四通道中有一个通道响应明显滞后

通道2在接通开路电压后，应该如其他通道一般迅速到达哦5v而现在是缓慢增长，电容充电过慢的嫌疑

原因：电桥的探测信号线接触异常，松动，压紧解决

导出干净的requirement 文件

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pip freeze | grep -v "@" | grep -v ".whl" > requirements.txt

实现了线性纳米线控制（使用电压阈值

Reference

DIY Arduino Oscilloscope | Arduino Project Hub

知识点记录：

Understanding Key Components for Arduino Oscilloscope Project

Analog-to-Digital Converters (ADCs)

An ADC converts continuous analog signals (like voltage) into discrete digital values that your microcontroller can process. Think of it as a translator between the analog world (your input signals) and the digital world (Arduino).

Key ADC Specifications to Consider:

  1. Resolution: Measured in bits (8-bit, 10-bit, 12-bit, etc.)

    • Arduino Uno/Nano: 10-bit (1024 values from 0-1023)
    • Arduino Due: 12-bit (4096 values from 0-4095)
    • External ADCs like ADS1115: Up to 16-bit

  2. Sampling Rate: How many conversions per second

    • Arduino Uno/Nano: ~10,000 samples/second maximum
    • Arduino Due: ~1,000,000 samples/second maximum
    • ESP32: ~2,000,000 samples/second maximum

  3. Input Range: The voltage span that can be measured

    • Arduino boards typically handle 0-5V or 0-3.3V
    • For your oscilloscope, you might need to detect signals outside this range

External ADC Options for Your Project:

  • ADS1115: 16-bit precision, but slower (~860 samples/second)
  • ADS1015: 12-bit, faster (~3,300 samples/second)
  • MCP3208: 12-bit, 8 channels, SPI interface (~100,000 samples/second)

Operational Amplifiers (Op-Amps)

Op-amps are versatile analog components that will help you condition your input signals before they reach the ADC.

Why You Need Op-Amps:

  1. Signal Conditioning: Adjusting voltage levels to match ADC input range
  2. Impedance Buffering: Preventing your measurement circuit from affecting the signal
  3. Filtering: Removing unwanted noise
  4. Amplification: Boosting weak signals
  • MCP6004: Quad op-amp (4 channels), rail-to-rail operation, works with 5V supply
  • LM324: Affordable quad op-amp, but not rail-to-rail
  • TL074: Good for audio frequencies, low noise
  • AD8607: Precision, low-noise, but more expensive

Basic Op-Amp Circuit for Your Project:

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Input Signal ----[R1]----+----[R2]----+
                          |            |
                          |            |
                          +---[Op-Amp]---> To Arduino ADC
                                |
                                |
GND --------------------------+

This is a basic non-inverting amplifier where gain = 1 + (R2/R1).

For a 4-channel system, you’ll need one op-amp circuit per channel. The MCP6004 contains four op-amps in one package, making it ideal for your application.

Direct Port Manipulation (DPM) and Finding Addresses

DPM lets you directly access microcontroller registers for faster I/O operations than using standard Arduino functions.

Finding Register Addresses:

  1. Consult the microcontroller datasheet:

  2. For Arduino Due specific to ADC registers:

    • ADC->ADC_MR: ADC Mode Register (controls ADC behavior)
    • ADC->ADC_CHER: ADC Channel Enable Register (enables specific ADC channels)

  3. For Arduino Uno/Mega:

    • ADMUX: ADC Multiplexer Selection Register (selects input channel)
    • ADCSRA: ADC Control and Status Register A (controls ADC operation)

Example of Finding and Using These Addresses:

For Arduino Due, the registers are already defined in the SAM3X library headers. You can directly use:

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ADC->ADC_MR |= 0x80;  // Set FREERUN mode
ADC->ADC_CHER = 0x0F; // Enable channels 0-3

For Arduino Uno/Mega, you would use:

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ADMUX = (ADMUX & 0xF0) | (channel & 0x0F); // Select ADC channel
ADCSRA |= (1 << ADSC);  // Start conversion

Understanding 0xFF and Hexadecimal Notation

0xFF is a hexadecimal (base-16) representation of the decimal number 255 (or binary 11111111).

Hex Notation Explained:

  • 0x prefix indicates a hexadecimal number
  • Hex uses digits 0-9 and letters A-F (representing values 10-15)
  • Each hex digit represents 4 bits

Common Hex Values in Microcontroller Programming:

  • 0xFF = 255 (all 8 bits set to 1)
  • 0x00 = 0 (all 8 bits set to 0)
  • 0x0F = 15 (lower 4 bits set to 1, upper 4 bits set to 0)
  • 0xF0 = 240 (upper 4 bits set to 1, lower 4 bits set to 0)

How It’s Used in Your Code:

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// In binary packet creation:
packet[0] = (timestamp >> 24) & 0xFF; // Extract highest 8 bits

Here, & 0xFF is a bitwise AND operation that masks out all but the lowest 8 bits, ensuring you only get one byte of data.

Direct Memory Access (DMA)

DMA is a feature that allows data transfers between memory and peripherals without using the CPU, freeing it for other tasks.

Benefits for Your Oscilloscope Project:

  1. Higher Throughput: Can continuously stream ADC samples to memory
  2. Reduced CPU Load: CPU doesn’t need to manually fetch each sample
  3. More Consistent Timing: Sampling isn’t affected by other code execution
  4. Background Operation: Your main code can process data while new samples are being collected

Using DMA with Arduino Due:

The Arduino Due (with SAM3X8E) supports DMA through its Peripheral DMA Controller (PDC).

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// Basic DMA setup for ADC on Arduino Due
void setupADC_DMA() {
  // Enable the PMC for the ADC
  pmc_enable_periph_clk(ID_ADC);
  
  // Reset and configure ADC
  adc_init(ADC, SystemCoreClock, ADC_FREQ_MAX, ADC_STARTUP_FAST);
  adc_configure_timing(ADC, 0, ADC_SETTLING_TIME_3, 1);
  adc_configure_trigger(ADC, ADC_TRIG_SW, 0);
  
  // Configure channels
  adc_enable_channel(ADC, ADC_CHANNEL_0);
  adc_enable_channel(ADC, ADC_CHANNEL_1);
  adc_enable_channel(ADC, ADC_CHANNEL_2);
  adc_enable_channel(ADC, ADC_CHANNEL_3);
  
  // Set up DMA buffer
  adc_dma_buffer[0] = {0};
  
  // Configure PDC (DMA controller)
  PDC_ADC->PERIPH_PTCR = PERIPH_PTCR_RXTDIS | PERIPH_PTCR_TXTDIS; // Disable PDC
  PDC_ADC->PERIPH_RPR = (uint32_t)adc_dma_buffer;  // Receive pointer
  PDC_ADC->PERIPH_RCR = BUFFER_SIZE;              // Receive counter
  PDC_ADC->PERIPH_PTCR = PERIPH_PTCR_RXTEN;       // Enable receiver
  
  // Enable ADC interrupt when buffer is full
  adc_enable_interrupt(ADC, ADC_IER_ENDRX);
  NVIC_EnableIRQ(ADC_IRQn);
}

For ESP32 (Alternative with Better DMA):

The ESP32 has excellent DMA capabilities through its I2S peripheral, which can be repurposed for ADC sampling:

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#include "driver/i2s.h"
#include "driver/adc.h"

#define SAMPLE_BUFFER_SIZE 1024

// Setup I2S with DMA for ADC reading
void setup_i2s_adc() {
  i2s_config_t i2s_config = {
    .mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_RX | I2S_MODE_ADC_BUILT_IN),
    .sample_rate = 20000,               // 20kHz sampling rate
    .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,
    .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
    .communication_format = I2S_COMM_FORMAT_I2S_MSB,
    .intr_alloc_flags = ESP_INTR_FLAG_LEVEL1,
    .dma_buf_count = 4,
    .dma_buf_len = SAMPLE_BUFFER_SIZE,
    .use_apll = false,
    .tx_desc_auto_clear = false,
    .fixed_mclk = 0
  };
  
  i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL);
  i2s_set_adc_mode(ADC_UNIT_1, ADC1_CHANNEL_0); // GPIO36
  i2s_adc_enable(I2S_NUM_0);
}

Putting It All Together for Your Oscilloscope

For your 4-channel oscilloscope with 10ms signal detection and sub-1s latency requirements, I recommend:

  1. Hardware: Arduino Due or ESP32 for their better ADC capabilities and DMA support
  2. Signal Conditioning: One MCP6004 quad op-amp configured for appropriate scaling
  3. Sampling Strategy: Use DMA for continuous acquisition
  4. Data Transfer: Binary packet format for efficient USB communication

The key to meeting your performance requirements will be optimizing both the sampling rate (which needs to be at least 100Hz for 10ms resolution) and the data transfer protocol to maintain latency under 1 second.

Would you like me to elaborate further on any of these aspects or provide a more complete implementation example?

Understanding AREF (Analog Reference) Function in Microcontrollers

AREF, which stands for Analog REFerence, is a critical function in microcontrollers that establishes the voltage reference point for analog-to-digital conversions. This reference voltage directly affects the accuracy and range of your analog sensor readings.

How AREF Works

When a microcontroller like Arduino reads an analog signal, it compares the input voltage to a reference voltage. The analog-to-digital converter (ADC) then maps this voltage to a digital value within its resolution range (typically 0-1023 for 10-bit ADCs).

For example, with a 5V reference:

  • 0V input → digital value 0
  • 2.5V input → digital value 512 (approximately half)
  • 5V input → digital value 1023 (maximum)

However, if you change the reference to 3.3V:

  • 0V input → still digital value 0
  • 1.65V input → digital value 512
  • 3.3V input → digital value 1023

AREF Sources in Arduino

Microcontrollers typically offer several reference voltage options:

  1. DEFAULT: Usually 5V (or 3.3V on 3.3V boards)
  2. INTERNAL: An internal reference (often 1.1V on ATmega chips)
  3. EXTERNAL: Voltage applied to the AREF pin (must be between 0V and VCC)

Why Use Different References?

Changing the reference voltage helps optimize precision for specific measurement ranges:

  • For small voltage measurements: Using a lower reference (like 1.1V internal) gives better resolution for small voltages.
  • For precise measurements: An external high-quality voltage reference can provide more accurate readings than the sometimes noisy power supply.
  • For battery-powered projects: Using internal reference avoids measurement drift as battery voltage decreases.

How to Use AREF in Arduino

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`// Set the analog reference to external 
analogReference(EXTERNAL); // Then read as normal 
int sensorValue = analogRead(A0);`

When using external reference, you must connect a stable voltage source to the AREF pin. This voltage must not exceed the microcontroller’s operating voltage (VCC).

Practical Implementation Tips

  1. Never change reference with AREF connected: Always disconnect external references before changing the reference mode to avoid damaging the microcontroller.
  2. Add capacitor for stability: A small capacitor (0.1μF) between AREF and GND can help stabilize the reference voltage.
  3. Precision matters: For higher accuracy, use precision voltage references like TL431 or dedicated reference ICs.
  4. First readings may be inaccurate: The ADC may need time to adjust after changing reference, so discard the first few readings.
  5. Match reference to sensor range: For a sensor outputting 0-3V, using a 3.3V reference will provide better resolution than a 5V reference.

Common Applications

  • Battery voltage monitoring: Using internal reference to measure battery voltage relative to a known value.
  • Temperature sensors: Many temperature sensors output small voltage changes that benefit from a lower reference.
  • High-precision instrumentation: Using a precision external voltage reference for consistent, accurate measurements.
  • Custom analog circuits: Creating specialized measurement ranges for specific analog sensors.

Understanding and properly utilizing AREF is essential for building precise analog measurement systems, especially in applications requiring high accuracy or working with specialized sensor ranges.

common use component prefix

Common IC Prefix Reference Chart

Prefix Manufacturer Represents Examples
LM National Semiconductor/TI Linear Monolithic LM741 (op-amp), LM555 (timer)
NE/SE Signetics (now NXP) NE = Commercial, SE = Military grade NE555 (timer), SE555 (high-reliability timer)
TL Texas Instruments Texas Linear TL071 (JFET op-amp), TL084 (quad op-amp)
UA/μA Fairchild Micro Amplifier UA741 (op-amp)
MC Motorola (now NXP) Motorola Commercial MC6800 (microprocessor), MC1458 (dual op-amp)
CD RCA/Various CMOS Digital CD4017 (counter), CD4066 (switch)
SN Texas Instruments Standard Numeric SN74LS00 (logic gate)
74/54 Various TTL Logic Family (74=commercial, 54=military) 7400 (NAND gate), 7404 (inverter)
MAX Maxim Integrated Maxim part MAX232 (RS-232 driver)
AD Analog Devices Analog Devices part AD620 (instrumentation amp)
ICL Intersil Intersil Commercial Linear ICL7660 (voltage converter)
OP Analog Devices/TI Operational Amplifier OP07 (precision op-amp)
CA RCA/Harris Commercial Amplifier CA3130 (CMOS op-amp)
XR Exar Corporation Exar part XR2206 (function generator)
LT Linear Technology (now ADI) Linear Technology part LT1001 (precision op-amp)
DS Dallas Semiconductor (now Maxim) Dallas Semiconductor part DS1307 (RTC)
IR International Rectifier IR part IRF540 (MOSFET)
HA Harris Semiconductor Harris Analog HA5102 (video amp)
KA Samsung/Korea Korea/Samsung Analog KA2206 (audio amp)
STK Sanyo/Panasonic Sanyo Thick Film Hybrid STK4141 (audio amp)
ULN TI/ST/Others Unisonic Linear Network ULN2003 (Darlington array)
AM AMD Advanced Micro Devices AM9511 (arithmetic processor)
MK Mostek Mostek part MK4116 (DRAM)
MM National Semiconductor Monolithic Memory MM5387 (clock chip)
HD Hitachi Hitachi Device HD44780 (LCD controller)
LS Various Low-power Schottky TTL 74LS04 (inverter)
HC Various High-speed CMOS 74HC00 (NAND gate)
AT Atmel/Microchip Atmel Technology ATmega328 (microcontroller)
PIC Microchip Peripheral Interface Controller PIC16F84 (microcontroller)
ADS Texas Instruments Analog-Digital Solutions ADS1115 (ADC)
FM Fairchild Fairchild Microdevices FM25L04B (FRAM memory)

Additional Common Prefixes for Discrete Components

Prefix Type of Component Examples
1N Diodes 1N4148 (signal diode), 1N4007 (rectifier)
2N Transistors 2N2222 (NPN), 2N3906 (PNP)
BC European Transistors BC547 (NPN), BC557 (PNP)
BD European Power Transistors BD139 (NPN), BD140 (PNP)
BF European RF Transistors BF199 (NPN)
IRF Power MOSFETs IRF510 (N-channel), IRF9540 (P-channel)
BAT Schottky Diodes BAT54 (Schottky)
TIP Power Transistors TIP31 (NPN), TIP32 (PNP)

Comprehensive IC Prefix Reference Chart

Digital & Analog Converters (DAC/ADC)

Prefix Manufacturer Represents Examples
DAC Various Digital-to-Analog Converter DAC0800 (8-bit DAC), DAC8408 (quad 8-bit DAC)
ADC Various Analog-to-Digital Converter ADC0804 (8-bit ADC)
MAX Maxim Maxim DACs/ADCs MAX5353 (10-bit DAC), MAX11613 (ADC)
MCP Microchip Microchip DACs/ADCs MCP4725 (12-bit DAC), MCP3008 (10-bit ADC)
PCM TI Audio DAC PCM1792 (audio DAC)
ADS TI Analog-Digital Solutions ADS1115 (16-bit ADC), ADS1298 (medical ADC)
LTC Linear Technology (now ADI) Linear Tech Converters LTC2624 (quad DAC)

Part Number (PN) Conventions

Manufacturer PN Format Meaning Example
Texas Instruments SN74LS00N SN=Standard, 74=Family, LS=Series, 00=Function, N=Package SN74LS00N (NAND gate, DIP package)
Microchip PIC16F877A-I/P PIC16=Family, F=Flash, 877A=Model, I=Temp Range, P=Package PIC16F877A-I/P (8-bit MCU, Plastic DIP)
Analog Devices AD8605ART AD=Company, 8605=Model, A=Grade, R=Package, T=Tape & Reel AD8605ART (Precision op-amp)
ST Microelectronics STM32F103C8T6 STM32=Family, F1=Series, 03=Line, C8=Flash size/pins, T6=Package STM32F103C8T6 (32-bit ARM MCU)
NXP MPXV7002DP M=Motorola, P=Pressure, X=Transducer, V=Voltage, 7002=Model, DP=Package MPXV7002DP (Pressure sensor)

Additional Common Prefixes

Prefix Manufacturer Represents Examples
ISO Various Isolation ISO7240 (digital isolator)
INA TI/Burr-Brown Instrumentation Amplifier INA128 (instr. amp)
REF Various Voltage Reference REF02 (5V reference)
PN Various PN Junction (Transistors) PN2222 (NPN transistor)
2SA/2SC Japanese 2SA=PNP, 2SC=NPN 2SC5200 (NPN power transistor)
DG Vishay/Siliconix Analog Switch DG408 (multiplexer)
OPA TI/Burr-Brown Operational Amplifier OPA627 (precision op-amp)
ICL Intersil Intersil Commercial Linear ICL7135 (ADC)
CS Cirrus Logic Cirrus Semiconductor CS4398 (audio DAC)

Where to Find This Information

  1. Manufacturer Datasheets and Websites:

  2. Component Distributors:

  3. Electronics Reference Sites:

  4. Books and References:

    • “The Art of Electronics” by Horowitz and Hill
    • “Linear & Digital IC Applications” by Carr
    • Electronics component handbooks from major manufacturers

  5. Online Tools: