[Upgraded version] Portable 8cm cooling fan

It has been verified and meets the free requirements and can be used directly on the board.
Principle: Control the duty cycle of the PWM signal output by the NE555 through a potentiometer to achieve speed regulation of the 4-wire fan.
Finished product (V2.1):
Function:
1. Independent switch controls the main power supply, that is, the speed regulating circuit. If the CONTROL switch (V2.2) or SPD switch (V2.1-) is turned to "OFF", the fan will run at full speed. .
2. Three 2835 (V2.2) or 5730 (V2.1-) lamp beads indicate the operating status (POWER/PWR_LED is the power indicator light, which lights up when the power is turned on; SPEED/SPD_LED is the pulse signal output by the fan speed feedback pin, the speed The faster, the faster the flashing speed; PWM/PWM_LED is the output signal of the NE555 chip, the brighter the light, the higher the duty cycle, and the faster the fan speed).
The reserved screw holes for the 3.8cm fan can directly fix the fan to the board.
4. Single chip design, NE555 is the only multi-pin chip (SOP8).
5. Reserve the + and - pads (located at the lower front). When the PWR switch is turned on, the battery voltage will be output. You can connect a voltmeter or power indicator module to monitor the battery status at any time (for the convenience of welding, there is no battery protection designed. circuit, so it is recommended to install a power monitoring device. When the fan speed slows down significantly, stop using it immediately and charge it in time. This circuit design is suitable for scenarios where you have an 18650 charger and excess 18650 lithium batteries at home. It can also be used for external power supplies (batteries). The box is not soldered, only the + and - pads are soldered. When using the + and - pads as power input, the reverse connection protection function will be lost. If the power supply is connected reversely, it may cause a plume of smoke, including but not limited to the fan and NE555).
6. Stepless speed regulation, wind power can be controlled at will (this function is only applicable to 4-wire PWM speed-regulated fans, and three-wire fans can only operate at full speed).
7. Use the dedicated 2510 terminal for the fan to prevent the fan power supply from being connected reversely. If you don’t have a 2510 terminal at home and don’t want to buy one, you can use an ordinary 2.54mm pin header instead (note: don’t connect it reversely!!!).
8. All 8cm fans are common (the fan in the picture is a 4500-turn four-wire CPU cooling fan with AVC size 8025 (80mm*80mm*25mm), and the TB price is about 8 yuan).
9. You can use a welded board and an empty board to form the shell without 3D printing (the upper board in the picture below is welded, and the fan wire passes through the gap below the battery box and above the bottom plate. The bottom board is an empty board without any components. It is recommended to use 2 screws to fix the top board with soldered components and 1 screw to fix the bottom board without soldered components).
There are two screws on the front:
there is only one screw on the back (the other hole is a magnetic bead, which can also be said to be a buck ball):
the battery can be replaced by rotating the back cover:
the buck ball (magnetic bead) can be on the back cover There is a crisp "snap" sound when rotated in place:
classic NE555 speed regulation circuit:
additional battery power display module (because there is a problem with the pad network of the V2.1 version, the + and - pads reserved on the front cannot be used, So I used enameled wire to fly the power display module to the solder joint of the switch on the back, and finally lit up the power display module (the voltage drop problem of the enameled wire has not been considered yet):
Close-up of the screw:
 
V2.1 update instructions:
1. Added switch The ON and OFF silkscreens on the side and the Slow and Fast silkscreens of the potentiometer are clear at a glance.
2. Fixed the problem of wrong direction of potentiometer.
3. Added SS34 Schottky diode to prevent reverse connection of the battery.
-------------------------------
V2.2 update instructions:
1. Fixed the problem of + and - pads connecting to the wrong network .
2. Fixed the problem of wrong pad network next to fan 2510 pin.