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Lorex 4K Camera



Step Motor

A4988 Step Motor Driver
Microstep settings

Stepper motors typically have a step size of 1.8° or 200 steps per revolution, this refers to full steps. A microstepping driver such as the A4988 allows higher resolutions by allowing intermediate step locations. This is achieved by energizing the coils with intermediate current levels.
For instance, driving a motor in quarter-step mode will give the 200-step-per-revolution motor 800 microsteps per revolution by using four different current levels. The resolution (step size) selector pins (MS1, MS2, and MS3) allow you to select one of the five step resolutions according to the table below.

Microstep resolution Setting
MS1 MS2 MS3 Microstep resolution
Low Low Low Full step
High Low Low 1/2 step
Low High Low 1/4 step
High High Low 1/8 step
High High Hgih 1/16 step

All three inputs have internal 100 kΩ pull-down resistors, so leaving the three microstep selection pins disconnected results in full-step mode.

Differences between the A4988 and DRV8825

The DRV8825 is quite similar to the A4988 but there are some key differences:

  • The DRV8825 offers 1/32 microstepping, whereas the A4988 only goes down to 1/16-step. Higher microstepping results in smoother, quieter operation but is not always needed.
  • The current limit potentiometer is at a different location
  • The relation between the reference voltage and the current limit is different.
  • The DRV8825 requires a minimum STEP pulse duration of 1.9µs; the A4988 requires 1µs minimum.
  • The DRV8825 can be used with a higher voltage motor power supply (45 V vs 35 V). This means it is less susceptible to damage from LC voltage spikes.
  • The DRV8825 can deliver slightly more current than the A4988 without any additional cooling.

Note that the pinout of the DRV8825 is exactly the same as for the A4988, so it can be used as a drop-in replacement! Both can work with 3.3 and 5v.

Cytron LCD Keyboard

Cricut Maker


3D Printer and CNC

Personal interest



Keep Idea

  • Create an universal assemble and disassemble instruction for everything
    • Every product must provide disassemble instruction.


Warning: Kickstart project

Sharing my journey

2019-Jul-17 Status

I would like to share some interesting things when I try to start this non-profit STEM club (CMEE4K).

  • After I announced to look for volunteers, two PhD joined: one Math and one Physics.

We are still looking for a space (room) for meeting.

  • Some churches and their community center rejected us because it is not church related activity.
  • City's community center rejected us because it is conflict with their STEM program.
  • After submitted 'Community Use of School' form to school board for a month, no respond.
  • Currently, we still talking to a library and a culture center.

Digital Divide

We have talking to an Immigration Services and a Youth Centre, here are their situation.

  • Their young (or clients) are from low incoming family.
  • Their family cannot effort ~$110 material fee.
  • They don't have a computer, and possibly no home internet access.
  • We were talking about fundraising. However, CMEE4K has no history and track record.

My observation

  • The IB school STEM club has 10K+ equipment, and their parents can pay $200-$300 club fee without problem.
  • Toronto GTA has many commerce STEM clubs (companies). The parents pay $35-$45 per session.
  • Most of them assume that the students have his/her own laptop. It is a norm for them.
  • Schools selected the high mark students into their STEM club (for Robotic competition).
  • Government funded NGO have STEM program but hard to find them, and have limited spots.
  • CMEE4K is Opened for everyone. If we mixing the paid and the fundraise-support students, will there a social conflict?

I recognized that STEM education is costly. The Digital Divide is difficult for the kids from low income family to catch-up with the rest. Then, they cannot escape from the loop.

李永乐老师 如何才能摆脱贫穷?穷人和富人有什么差别?【2019诺贝尔经济学奖解读】2019-Oct-28

YouTube: 如何才能摆脱贫穷?穷人和富人有什么差别?
2019年诺贝尔经济学奖 如何才能摆脱贫穷.png

  • Ratio: when increase parent education, children will increase education time.
  • Learning disability: Translate the text book from English to their language.
  • Risk / threshold: There is the minimum living cost (threshold) for them to escape / accelerate.
  • Their financial concept: How they use their (low) income.

I like to share the vision of 任正非


  • 把教育做好,国家才有未来
  • 社会重视基础教育,让教师成为最伟大的职业,成为优秀青年的向往。
  • 这个时代对一个国家来说,重心是要发展教育,而且主要是基础教育,特别是农村的基础教育。没有良好的基础教育,就难有有作为的基础研究。
  • 振兴教育不在房子,在于老师。
  • 物质不是最主要的,人才是最主要的,人类灵魂的工程师应该得到尊重,这个国家才有希望。
  • 任正非说:我认为,社会就是应该有口号“用最优秀的人去培养更优秀的人”,“我们再穷也不能穷老师”。

Diff country computer eduction.jpeg

My record