> For the complete documentation index, see [llms.txt](https://headtracker.gitbook.io/head-tracker-v2.2/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://headtracker.gitbook.io/head-tracker-v2.2/getting-started/wiring/ppm-input.md).

# PPM Input

### PPM Input

{% hint style="danger" %}
If you have a PPM signal that is higher than 3.3Volts you will need a voltage divider to reduce the signal. Otherwise you **!Will!** damage your BLE Nano 33.
{% endhint %}

Hook up as shown in the diagram below. To calculate R1 use the following formula.![](https://raw.githubusercontent.com/wiki/dlktdr/HeadTracker/media/ppm/VoltageDividerEquation.png)

For 5V PPM signal, R1 = (5\*10,000)/3.3 - 10,000 = 5151ohms Round the value **UP** to the nearest commonly available resistor, which is 5600ohm or 5.6k

For 7V PPM Signal, R1 = 7\*10,000/3.3 - 10,000 = 11,212 ohms ==> **Rounded Up** ==> 12,000ohm or **12Kohm**

It's better to have R value too big, this will result in a lower voltage on the output to our nano, which is okay as it should still be detected as a high level even if the pulse is lower than 3.3v.

{% hint style="info" %}
To be extra careful you could put a Zener diode in parallel with the 10K resistor. The Cathode (which is the side with the line) should attach D9, the other end to gnd. This will clamp any voltage that might climb above 3.3v.
{% endhint %}

![](https://1791219135-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-Md5nSb70RWQSfl1nJPs%2F-MfWjnFHdZcI6D6NO-HV%2F-MfWjp-DBZCKKGCc0_1k%2Fimage.png?alt=media\&token=dd9cc47b-8372-4d49-bab8-b739ea55004d)