Multifunctional test oscilloscope pen

1. Project Description
      : The CW32F030C8T6 is used as the main controller, powered by a battery, with a 0.96-inch screen display. It can communicate with a host computer via Bluetooth. Analog switches are used to switch input and output. The input voltage range is 0~+17V, and the output is 0~+6V DC.
Main functions include: 1. Voltage measurement and threshold judgment; 2. PWM and DC output; 3. Continuity detection with adjustable threshold resistance; measurement of diode forward voltage; 4. Simple oscilloscope function.
 
2. Main Functions
  : 1. Voltage Measurement and Threshold Judgment
        : Supports input from 0~+17V. A red light illuminates when the voltage is higher than the set threshold, and a blue light illuminates when it is lower than the threshold. The screen displays the measured voltage.
  2. PWM and DC Output:
        Supports direct PWM output with adjustable frequency and duty cycle. The PWM signal is filtered before being used as the DC output, with a DC output voltage of 0~+6V. The DC output also serves as the reference voltage for the comparator, used for the oscilloscope's trigger level and frequency measurement.
  3. Continuity Detection: Adjustable threshold resistor.
        The LM1117GSF-ADJ is used as a current source to measure the diode's forward voltage. A resistance below the threshold indicates conduction, indicated by a buzzer and blue light. The screen displays the forward voltage during diode measurement.
  4. Simple Oscilloscope Functions
      : Oscilloscope Menu Explanation: SC, SH, and TR on the right are the control menus. The three middle positions at the bottom display data, and the single letters on either side indicate status.

  SC: When SC is selected, pressing the middle button highlights SC in green. The up and down buttons control the waveform's scaling on the y-axis, and the left and right buttons control the waveform's scaling on the x-axis, controlled by the ADC clock frequency.
  SH: When SH is selected, the waveform can be moved along the x and y axes.
  TR: When TR is selected, the up and down buttons set the trigger level, the left button sets rising and falling edge triggering, and the right button sets single and multiple triggering.

 
3. Circuit Description
 
  1. Power
    On: Press the middle button, PW_ON is pulled low, Q1 conducts, BAT supplies power to the buck chip, the main control chip powers on, the pin connected to PW_CT is pulled high, Q2 conducts, the green light illuminates, and the middle button can be released to complete the power-on process.
    Power Off: Press and hold the middle button for 2 seconds, the PW_CT pin is pulled low, Q2 is cut off, release the middle button, Q1 is cut off, and the power-off process is complete.
 
  2.
       

    The analog switch chip HT4053A used for boost is 18V. To allow for some margin, the system voltage is designed at 17.5V, using MT3608 for boost. When laying out the PCB, pay attention to the isolation between analog ground and digital ground,
    the inductor should be close to the chip, and the feedback circuit should be away from interference sources.
 
  3. Output Circuit
      : There will be a voltage drop when the PWM filter is converted to DC. After being amplified by 2 times by the amplifier, the output is 0~+6V, and then after a first-order filter, it is output or directly fed into the comparator.
 
  4.
      The DC output of the comparator circuit serves as the reference voltage for the hysteresis comparator. The inverting terminal is the input voltage, which can be used to measure the frequency of the input signal. Note that the timer must be selected in rising or falling edge mode and the settings must be inverted.
 
  5. The current source
    uses an LM1117GSF-ADJ, with a control current of 2mA. R55 is the bleeder resistor for C31. The 17.5V is stepped down to 5V by an LDO and input to the LM1117GSF-ADJ.
   
  6. Bluetooth
        allows communication with a host computer. Bluetooth remote control or mouse/keyboard macro functions may be added later.
 
4.
        For ease of debugging, the resistor connected to PW_ON is grounded to keep the chip constantly powered.
 
    The PWM output shows spikes on both rising and falling edges; this is still being studied.
 
    A screen rotation function has been added to facilitate left- or right-handed use.
 
  More demos on Bilibili: https://www.bilibili.com/video/BV1vb4y1M7PK
 
My thoughts: Through this training camp, I was introduced to amplifiers, comparators, and DC-DC converters for the first time, and also gained a basic understanding of the principles of oscilloscopes. It was truly a very rewarding experience. Thank you!