Introduction

I don’t need to elaborate on what it is used for and how to use it. Taobao has a lot of similar products.

Function: Output 50Hz pulse, pulse width adjustable from 0.5ms to 2.5ms.

working principle

The first part is actually the same model as the LM358 breathing light circuit.

U1.2 and its peripheral components form a low-pass filter, and the op amp may be used as a constant current source to charge and discharge the capacitor, so the triangle wave will be straighter than the oscillating triangle wave of NE555.

RV1 adjusts the charge and discharge current, thereby changing the triangular wave frequency.

U1.1 and peripheral components form a non-inverting Schmitt trigger, and the trigger level is the divided voltage of R4 and R5.

The second part is a comparison circuit

The second part is to compare the triangle wave with a reference voltage to generate PWM.

The waveform will be added later. Please refer to SPWM for the specific implementation process.

Debugging results

Note that some SMD components are used and soldered on the back of the actual product. In reality, there are components, not without soldering.

Component selection

Some people may think that these circuits are a bit extravagant compared to Taobao kits.

But in fact, if the quantity is large, placing orders yourself will not be much more valuable than Taobao.

As a soldering learning board, it is recommended to choose the cheapest electronic components. Can support domestic chips.

Because the component fails, the process of troubleshooting further tests whether you have a thorough grasp of the principles.

related suggestion

The potentiometers and chips between these circuits are universal. If a certain circuit is damaged, the east wall can be removed to repair the west wall.

Sorted from simple to difficult, teachers are welcome to use them in teaching, but we hope that the URL of this open source page will be added to the courseware to show respect, thank you.

Analog circuit

1. NE555 Ambilight RGB driver
2. LM358 infrared sensor faucet circuit
3. NE555 dormitory magic lamp driver circuit
4. LM358 running water breathing lamp
5. LM358 pickup delay circuit
6. LM358 refrigerator closing reminder circuit
7. LM358 steering gear tester circuit
8. NE555 steering gear tester circuit
9. Dual-way Wien bridge sine wave generating circuit
10. NE5532 infrared reflective switch plus bandpass filtering
11. NE5532 music spectrum light

power circuit

1. Transistor constant voltage and constant current linear power supply
2. MC34063 single inductor buck-boost power supply
3. MC34063 temperature controlled fan
4. MC34063 light control lighting
5. LM358 constant voltage and constant current power supply

Digital circuits

1. CD4017 music doorbell
2. 74LS00 builds JK flip-flop
3. CD4013 three-person answering machine
4. CD4017 running water lamp clock