working principle

clock source

The power frequency electromagnetic radiation is collected by the antenna and shaped by NE555 into a 50Hz square wave.

Frequency division

U2 divides 50Hz by 10 to become 5Hz, and then U3 divides 50Hz by 5 to become 1Hz, which is used to provide second travel time later.

Display and hexadecimal

This is a second display circuit, and U4 divides it by 10. And display the ones digit of the second.

U5 divides the frequency by 6 to couple the minutes to the next level.

Hexadecimal and display

U9 divides the hour by two, and is reset by an AND gate composed of D1, D2, and R5.

When 12 o'clock, RST is high, U8 is reset, hour0 outputs high again, hour00 flips again, providing signals for AM and PM later.

Low brightness at night

From 6 am to 6 pm, !Q output is low, and it is full brightness at this time. On the contrary, it is only half the brightness.

In the implementation process, at 6 o'clock, the AND gate is enabled and the status of morning and afternoon is transmitted to the subsequent RS flip-flop to achieve the self-locking function.

Continuous triggering of keys

When the button is pressed, the previous 5Hz will be output to the clock terminal of CD4017 through the button for counting. In order to prevent the two output ports from being short-circuited, a 10k resistor is added to limit the current.

Usage details

Because most schools now replace fluorescent lamps with LEDs and do not have inductive ballasts, the power frequency radiation signal in the training room is relatively weak.

It is possible that 50Hz cannot be received at certain locations and angles. It is recommended to place it near a socket or extend the antenna when using it.

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