# UART

<figure><img src="/files/zbazOx7JDYsTmucXDNU3" alt=""><figcaption></figcaption></figure>

There is a TX and RX pin on all Head Tracker boards that can be used for SBUS or CRSF. There is currently three options supported.

### **SBUS in + out**

<figure><img src="/files/i6uChmQwwAqFFHobRF0z" alt=""><figcaption></figcaption></figure>

* Some radios support SBUS as a Trainer option, this is a digital system, fast and accurate. If you have it available it's preferred over PPM.
* It will allow you to transmit 16 channels on the **TX pin**
* You can also receive 16 channels on the **RX pin**
  * Receive can be used if you need to connect more than one Head Tracker to your radio. It can support a much faster update rate.
* Invert - These will invert the SBUS signal either RX or TX.&#x20;
  * On the **Nano33BLE series** of boards there is a limitation on the NRF52840 processor SBUS input requires you to solder D5 and D6 together for invert to work. **If your unsure if you need not-inverted** just solder them together when assembling, it won't hurt anything.
  * The **DTQSYS** board has this done internally, please ignore the message. It will be corrected in the next GUI.

### **CRSF Input**

<figure><img src="/files/NnNWF2IAPgFKs7yOyLE8" alt=""><figcaption></figcaption></figure>

* Allows you to receive channels using the CRSF protocol. There are no options to configure here. CRSF should be attached to the TX and RX pins. Not sure of a use for this yet but it's here is someone wants it :tada:
* Could be used to hook two Head Trackers together wirelessly using a ELRS TX & RX, but since you can't transmit and receive at the same time would need to have a wired connection to the radio.

### **CRSF Output**

<figure><img src="/files/SWfIQwhsz3hhUSA59GgH" alt=""><figcaption></figcaption></figure>

* **Update Rate**&#x20;
  * This is the rate the channels are updated at. **Leave this at the maximum** unless you have a custom application.
* **Use channel 5 as AUX1/ARM**
  * This option will force channel 5 to be always on at 2000us. <mark style="color:red;">**This is needed for an ELRS transmitter**</mark>. ELRS uses this channel for reasons listed ->[**Here**](https://www.expresslrs.org/software/switch-config/#why-do-you-keep-saying-put-arm-on-aux1). If your using **Crossfire** or **Tracer** leave this **un-checked**.
* **CRSF Output Level**

  * This will invert the TX pin signal, if your using a <mark style="color:red;">**JR Bay type transmitter**</mark>**&#x20;(Crossfire, Tracer or ELRS)** this <mark style="color:red;">**needs to be checked**</mark>. You should hook the <mark style="color:red;">**TX pin**</mark> on the Head Tracker to <mark style="color:red;">**S.PORT pin**</mark> on the JR module. <mark style="color:red;">**RX on the HT is not connected**</mark>. You will also connect **GND**(**HT**) -> **GND (Module)**. You will also need a way to power it on the VMAIN pin, that one is up to you :smile:

  <figure><img src="/files/hBlJzQx6sFT0a7G7OW0X" alt="" width="188"><figcaption></figcaption></figure>

  * If connecting to a **ELRS receiver** that has been **flashed to be a transmitter**, leave this box **un-checked**. For instance the Happy Model EP2 [ELRS Setup](/head-tracker-v2.2/getting-started/wiring/elrs-setup.md) which can be used as a trainer link.


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