This article comes from the breadboard community teardown event!
Preface
The company gave away a waist massager during the holidays, but it was hardly used. After searching the price, it seemed that it was more than 100. I personally feel that it is a bit of a waste. It would be better to just send the money. I was curious about how its structure and control were done, so I took it apart and analyzed it, which can be regarded as making the best use of the remaining heat.
dismantle
Personally I think the appearance and color scheme are okay, relatively youthful.
Open the zipper and take apart the outer cloth. There is still a layer of gauze inside.
The buttons are fixed with Velcro
After taking apart the gauze, you can see the structure inside. The whole thing is a sponge.
You can see the following, the three leads of the battery, key board, and charging cable
The battery is installed in a component box. Double-sided tape is used to fix it. The outside is fixed with transparent tape. I also use scissors to open the wire trough. I use a cheap component box directly. I don’t have to open a mold to specially design the box. It’s considered a good idea. How come it's cheap?
Unscrew the screws on the massage head. The heating plate is located inside the massage head. The two spring contacts contact the two annular copper rings below. The copper rings are then wired to the PCB board. Here, because the heating plate needs to rotate on the massage head, the contact method of spring contact + copper ring is used to achieve rotation and conduct electricity.
On the motherboard, you can see several sockets for heating, motor, and battery.
I measured the battery voltage and found it was only 6.3V. Two 3.7V batteries connected in series should normally be above 7.4V, so it needs to be charged.
Continue to remove the 8 screws on the motor, and you can see the reduction gears on both sides. The motor is a 7.4V DC motor.
Main control circuit analysis
The MCU and battery charging chip on the motherboard have been polished, not sure about the model.
Two pieces of STC4614: N+P MOS tubes are used for motor control. The two pieces form an H-bridge driver, which can rotate forward and reverse.
Use the S8050 transistor with silk screen J3Y to control the MOS switch
The silk screen BE is a 12V unidirectional SMA transient suppression diode, which is used for MOS freewheeling.
The diode of M7 prevents voltage backflow
The 3.3V voltage regulator chip has also been polished and the model is uncertain.
Silk screen A0H MOS tube is used to control heating
Button LED circuit analysis
The button board design is quite interesting. There are three buttons and 5 LEDs that actually only use 4 wires + one GND.
This design reduces the number of signals and lines and is worth learning from.
If you press a button, you actually use the ADC to collect it.
When KEY3 is pressed only, the voltage at KEY is 0V.
When only KEY2 is pressed, the voltage at KEY is 3.3V*10K/20k=1.65V
When only KEY1 is pressed, the voltage at KEY is 3.3V*20K/30K=2.2V
Therefore, if the button is not pressed, the KEY voltage is 3.3V.
3 LED signals control 5 LED lights
One IO controls two LEDs. When the IO output is low and high, the two LEDs light up respectively. When the output is in the high-impedance state, neither light up (the combined turn-on voltage of the two LEDs connected in series is greater than VCC, but it may light up weakly. On the actual board It can also be observed), both LEDs output high-frequency square waves are on, so you can see that one IO can control the two-color light to display different colors.
The two above two-color LEDs are controlled in this way, and there is also a charging indicator LED that is controlled separately.
I have posted some LED light control circuits before
The ultimate tutorial, with specific experimental phenomena, 1 GPIO controls 2 LEDs to display 4 states, welcome to discuss! (click to read)
excellent! 1 GPIO controls 2 LEDs to display 4 states, what? You do not believe? (click to read)
In fact, there are also Charlie multiplexed circuits. There are special articles on the Internet for analysis, so I won’t go into details. You can also refer to them. (See the article on the public account)
Summarize
A distinctive feature of the structure is that the spring contacts realize rotating contact.
The design of button and LED control is worth learning from, using fewer signals to achieve multiple button collection and LED control.
The main control is mainly the H-bridge controlling the DC motor, nothing special.
Recommended in the past
[Hard-core dismantling ] Can the 2022 summer smart power saver save electricity?
Fake Macbook charger teardown : convincing on the outside but dangerous on the inside