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Helios64 Hardware Detailed Info (#27)

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* Add detailed hardware info for Helios64
    - Button
    - Ethernet
    - Front Panel
    - GPIO
    - I2C
    - Jumper
    - LED
    - M.2
    - PMIC
    - PWM Fan
    - RTC
    - SATA
    - SPI
    - UEXT
    - UPS
    - USB

* Cosmetic upgrade and adapt to latest mkdocs-material version

Co-authored-by: nurix <nurix@pnsnc.local>
Co-authored-by: Aditya Prayoga <aditya@kobol.io>
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Gauthier Provost 2020-04-20 16:06:24 +08:00 • committed by GitHub
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## PWM Introduction
PWM, or pulse width modulation is a technique which allows us to adjust the average value of the voltage that’s going to the electronic device by varying duty cycle of the power at a fast rate.
The term *duty cycle* describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on. When a digital signal is on half of the time and off the other half of the time, the digital signal has a duty cycle of 50% and resembles a "square" wave. When a digital signal spends more time in the on state than the off state, it has a duty cycle of >50%. When a digital signal spends more time in the off state than the on state, it has a duty cycle of <50%. Here is a pictorial that illustrates these three scenarios:
![PWM duty cycle](/helios64/img/pwm/pwm_duty_cycle_graph.png)
## PWM Fan Implementation
### Type-A
![Type A Curve](/helios64/img/pwm/fan_type_a_curve.jpg)
### Type-B
![Type B Curve](/helios64/img/pwm/fan_type_b_curve.jpg)
### Type-C
![Type C Curve](/helios64/img/pwm/fan_type_c_curve.jpg)
## PWM Fan Schematic
![!Fan Control Schematic](img/pwm/fan_control_schematic.png)
**Remarks**
| Description | Header P7 | Header P6 | Remarks |
|-----------|---------|-----------|---------|
| PWM pin | PWM0 | PWM1 | 5V tolerant |
| SENSE pin | GPIO4_C5 | GPIO4_C7 | no kernel module/userspace apps that make use of this pin yet |
| PWM Frequency | 25 kHz | 25 kHz | defined in device tree |
## PWM Fan Connector
![Fan Connector](/helios4/img/pwm/fan_connector.png)
Connector Pinout
| Pin | Function | Wire Color |
|-----|----------|------------|
| 1 | GND | Black |
| 2 | 12V | Red |
| 3 | Sense | Yellow |
| 4 | Control | Blue |