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OTG HDMI Adapter
==========================================

.. image:: img/hdmi_adapter.jpeg

This USB HDMI adapter board is specifically designed for the Raspberry Pi 5. Its primary function is to reposition the USB and HDMI connections to align with the USB interface side of the Raspberry Pi, enhancing accessibility and cable management.

Additionally, the HDMI port is converted to a standard HDMI Type A interface, offering broader compatibility.


**OTG**

The OTG interface utilizes the USB Type-C port on the Raspberry Pi to enable OTG (On-The-Go) functionality. This feature adds an additional front-facing USB 2.0 port, making it convenient to quickly connect and use simple USB devices.

By default, OTG functionality is not enabled in the system. However, it is automatically activated after installing the Pironman 5 software. If needed, you can manually enable it by modifying the ``/boot/firmware/config.txt`` file:

.. code-block:: bash

  dtoverlay=dwc2,dr_mode=host


This line configures the USB controller to operate in host mode, which is required for OTG functionality. Be sure to reboot the system after making changes to the configuration file for them to take effect.



**1220RTC Battery Holder**

A 1220RTC battery holder is incorporated for convenient installation of an RTC battery. It connects to the Raspberry Pi's RTC interface via an SH1.0 2P reverse cable. 

The battery holder is compatible with both CR1220 and ML1220 batteries. If using an ML1220 (Lithium Manganese Dioxide battery), charging can be configured directly on the Raspberry Pi. Note that the CR1220 is not rechargeable.

**Enabling Trickle Charging**

.. warning::

  If you're using a CR1220 battery, do not enable trickle charging as it can cause irreparable damage to the battery and risk damaging the board.

By default, the trickle charging feature for the battery is disabled. The ``sysfs`` files indicate the current trickle charging voltage and limits:

.. code-block:: shell

    pi@raspberrypi:~ $ cat /sys/devices/platform/soc/soc:rpi_rtc/rtc/rtc0/charging_voltage
    0
    pi@raspberrypi:~ $ cat /sys/devices/platform/soc/soc:rpi_rtc/rtc/rtc0/charging_voltage_max
    4400000
    pi@raspberrypi:~ $ cat /sys/devices/platform/soc/soc:rpi_rtc/rtc/rtc0/charging_voltage_min
    1300000

To enable trickle charging, add ``rtc_bbat_vchg`` to ``/boot/firmware/config.txt``:

  * Open the ``/boot/firmware/config.txt``.
  
    .. code-block:: shell
    
      sudo nano /boot/firmware/config.txt
      
  * Add ``rtc_bbat_vchg`` to ``/boot/firmware/config.txt``.
  
    .. code-block:: shell
    
      dtparam=rtc_bbat_vchg=3000000
  
After rebooting, the system will display:

.. code-block:: shell

    pi@raspberrypi:~ $ cat /sys/devices/platform/soc/soc:rpi_rtc/rtc/rtc0/charging_voltage
    3000000
    pi@raspberrypi:~ $ cat /sys/devices/platform/soc/soc:rpi_rtc/rtc/rtc0/charging_voltage_max
    4400000
    pi@raspberrypi:~ $ cat /sys/devices/platform/soc/soc:rpi_rtc/rtc/rtc0/charging_voltage_min
    1300000

This confirms the battery is now under trickle charging. To disable this feature, simply remove the ``dtparam`` line from ``config.txt``.