> For the complete documentation index, see [llms.txt](https://beyond-robotix.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://beyond-robotix.gitbook.io/docs/can-ecosystem/l431-can-node.md).

# CAN Node

A standalone STM32L431 CAN node for converting sensors to DroneCAN

## Overview

This is a standard form factor variant of our Micro Node for projects which require less customisability but still with lots of features accessible, and the handy debug port for developing Arduino DroneCAN applications.

With its mounting holes & 2.54mm header it can be integrated robustly into your projects.

{% embed url="<https://www.beyondrobotix.com/products/can-node>" %}

* Debug interface for easy Arduino DroneCAN development (Serial+SWD)
* M2 18x20mm mounting holes
* LED indicators
* JST-GH connector interfaces
  * 1x CAN interface with two CAN connectors for daisy chaining
  * 1x Serial
  * 1x i2c
* 2.54mm pitch general breakouts including:
  * CAN (same interface as the JST-GH)
  * Additional serial
  * 5 ADCs
  * 6 PWMs
  * i2c (same interface as JST-GH)
  * 5v
  * 3.3v
* Power input dioded + fused

<div><figure><img src="https://1239082692-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FdPR57GIwyNGpujTZHIUm%2Fuploads%2FgwPdBdvCSveKThu2E98K%2Fwhite-Photoroom(1).png?alt=media&amp;token=b515b61b-c826-4a43-ac52-4a4215e86456" alt="" width="375"><figcaption></figcaption></figure> <figure><img src="https://1239082692-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FdPR57GIwyNGpujTZHIUm%2Fuploads%2Fr1wW4pJnhkzdRmmioMJA%2Fwhite-Photoroom(2).png?alt=media&amp;token=b092a2f9-8cc9-471b-a828-8f28154a5acf" alt="" width="375"><figcaption></figcaption></figure></div>

## Specifications

| Item       | Detail                                                                                     |
| ---------- | ------------------------------------------------------------------------------------------ |
| MCU        | STM32L431                                                                                  |
| Flash      | 256 KB total                                                                               |
| CAN        | 1x CAN1 (Classic CAN, no CAN FD)                                                           |
| Crystal    | 8 MHz external oscillator                                                                  |
| Dimensions | 18 x 20 mm (see [Mounting holes & Board dimensions](#mounting-holes-and-board-dimensions)) |

## Firmware

The board is primarily designed to be used with our **Arduino DroneCAN** library, so you can write your own firmware around your sensor with minimal boilerplate. It also ships with **AP\_Periph** firmware by default, ArduPilot's ready-made DroneCAN peripheral firmware, for when no custom firmware is needed.

### Arduino DroneCAN

The recommended way to build custom firmware for this board. Handles the DroneCAN plumbing for you, so integrating a new sensor is usually a small amount of code.

{% content-ref url="/pages/M2zud63qLgUMPxkA6gng" %}
[Arduino DroneCAN](/docs/can-ecosystem/arduino-dronecan.md)
{% endcontent-ref %}

### AP\_Periph (default shipped firmware)

Every board ships with a generic AP\_Periph build by default. It requires no code and supports a wide range of common sensors out of the box.

#### Default firmware features

* **Servo/PWM output** — 6 channels, see [PWM](#pwm) below
* **GPS** — moving-baseline support, Septentrio SBF driver enabled, output on Serial 3 by default
* **Airspeed (I2C)** — MS4525 sensor as default type
* **Battery monitor** — analog voltage/current sensing, disabled by default, enable via DroneCAN parameters
* **Relay output**
* **Serial ESC passthrough**

#### Servo / PWM outputs (channels 1–6)

| Pin  | RCOut Channel (OUTn\_) |
| ---- | ---------------------- |
| PA0  | 1                      |
| PA1  | 2                      |
| PA8  | 3                      |
| PA9  | 4                      |
| PA10 | 5                      |
| PA11 | 6                      |

Outputs 1–2 are driven by TIM2 (general-purpose timer), outputs 3–6 by TIM1 (advanced timer).

| Parameter               | Purpose                                      | Notes                                                                                             |
| ----------------------- | -------------------------------------------- | ------------------------------------------------------------------------------------------------- |
| `OUTn_FUNCTION`         | Assigns output function to channel *n* (1–6) | `0` = Disabled. See `SRV_Channel::Aux_servo_function_t` for full list (e.g. Motor1, RCIN1, GPIO). |
| `OUTn_MIN` / `OUTn_MAX` | PWM endpoint range (µs)                      | Per channel                                                                                       |
| `OUTn_TRIM`             | Trim/neutral PWM (µs)                        | Per channel                                                                                       |
| `OUTn_REVERSED`         | Reverse output direction                     | Per channel                                                                                       |
| `ESC_RATE`              | Update rate for ESC/motor outputs            | Default 400 Hz                                                                                    |
| `ESC_PWM_TYPE`          | Output protocol (OneShot/DShot/etc.)         | Default 0 (normal PWM)                                                                            |

Relay/GPIO output can reuse these same pins (GPIO 50–55) when the corresponding `OUTn_FUNCTION` is set to `-1`/GPIO instead of a servo function.

### ADC

The following pins can be used as ADCs. The channel is what is used to identify the pin in AP\_Periph, for example for the `BATT_VOLT_PIN`

| Hardware Pin | ADC Channel |
| ------------ | ----------- |
| A0           | `5`         |
| A1           | `6`         |
| A4           | `9`         |
| B0           | `15`        |
| B1           | `16`        |

{% hint style="danger" %}
The maximum voltage of the ADC pins is 3.3V.
{% endhint %}

#### Battery monitor

| Parameter         | Purpose                                                       | Default           |
| ----------------- | ------------------------------------------------------------- | ----------------- |
| `BATT_MONITOR`    | Monitor type (`0`=Disabled, `4`=Analog Voltage+Current, etc.) | `0` (disabled)    |
| `BATT_VOLT_PIN`   | ADC pin for voltage sense                                     | `5` (maps to PB0) |
| `BATT_VOLT_MULT`  | Voltage divider scale                                         | `21.0`            |
| `BATT_CURR_PIN`   | ADC pin for current sense                                     | `6` (maps to PB1) |
| `BATT_AMP_PERVLT` | Current sensor scale (A/V)                                    | `40.0`            |

Set `BATT_MONITOR` to a nonzero type to enable; the pin/scale defaults above already match the onboard sense resistors/divider, but can be overridden per-install if a different sensor is wired.

#### Airspeed (I2C)

| Parameter    | Purpose       | Default                              |
| ------------ | ------------- | ------------------------------------ |
| `ARSPD_TYPE` | Sensor type   | `1` = MS4525                         |
| `ARSPD_BUS`  | I2C bus index | Auto-detected on the onboard I2C bus |

#### GPS

| Parameter          | Purpose                                                 | Default                 |
| ------------------ | ------------------------------------------------------- | ----------------------- |
| `GPS1_TYPE`        | GPS protocol/type                                       | Auto-detect on Serial 3 |
| `GPS_PORT`         | DroneCAN GPS output port index                          | `2`                     |
| `GPS_MB_ONLY_PORT` | Restrict moving-baseline pairing to a specific CAN port | `0` (disabled)          |

Moving-baseline and Septentrio SBF support are compiled in; no extra param is needed to enable the driver itself, only to select the correct `GPS1_TYPE`.

#### Firmware files and flashing

If there is no AP\_Periph bootloader present on the node (you've been using Arduino DroneCAN, for example) then the `with bootloader` .hex needs flashing with STM32CubeProgrammer using STLINK or UART.

If the AP\_Periph bootloader is already present, the .bin file can be used in the usual way through Mission Planner.

{% file src="/files/5MAE7yHtOrcNtvrm4BgO" %}

{% file src="/files/pjQDCrRCzj2St0jkZ1v6" %}

For general background on AP\_Periph on our nodes, see:

{% content-ref url="/pages/tqI6YEG36OVJmIvNEEFt" %}
[AP Periph](/docs/can-ecosystem/ap-periph.md)
{% endcontent-ref %}

## Mechanical

### CAD

Full CAD including connectors can be found here:

{% file src="/files/lIARwjJippRjdO42CZe2" %}

### Mounting holes & Board dimensions

Mounting holes are M2 (2.2mm diameter cutout)

Dimensions in mm:

<figure><img src="https://1239082692-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FdPR57GIwyNGpujTZHIUm%2Fuploads%2FYLTH8RczenCjsWVf5pkB%2Fimage.png?alt=media&amp;token=7db6849b-b73b-4a75-88ed-552133b8d88d" alt="" width="375"><figcaption></figcaption></figure>

## Pinout / Interfaces

### CAN

The CAN Node has 1 available CAN interface, which is pinned out to 2 JST-GH CAN ports, to allow CAN device chaining.

| Pin Number | Description |
| ---------- | ----------- |
| 1          | Vcc (5V)    |
| 2          | CANH        |
| 3          | CANL        |
| 4          | GND         |

### I2C

The CAN Node has 1 available I2C interface exposed to a JST-GH port.

{% hint style="warning" %}
The CAN Node V1.0 has no i2c pullups on board. I2C sensors attached to this interface will need pullups to function.
{% endhint %}

| Pin | Description |
| --- | ----------- |
| 1   | 5V          |
| 2   | SCL         |
| 3   | SDA         |
| 4   | GND         |

{% hint style="info" %}
The pins in the I2C JST-GH are common (the same interface) with the pins on the 2.54 mm header pins.
{% endhint %}

### Serial

The CAN node has 3 serial interface exposed. UART1 is exposed on the 2.54mm header pins, UART2 is exposed in the ST-LINK Debug header and UART3 is exposed on the JST-GH.

| Pin | Description |
| --- | ----------- |
| 1   | Vcc (5V)    |
| 2   | UART3\_TX   |
| 3   | UART3\_RX   |
| 4   | N/C         |
| 5   | N/C         |
| 6   | GND         |

## 2.54 mm Header

More interfaces can be accessed through the 2.54 mm header. Wires could be directly soldered to these pads, or header pins could be added.

The CAN interface is accessible through this header, as well as power input, allowing the board to be used purely through the header without needing the JST-GH connectors if desired.

The following interfaces aer pinned out on the headers:

* CAN interface (C\_L, C\_H)
* Power (5V, 3v3, 2x GND)
* UART1 (TX1, RX1)
* I2C interface (SDA, SCL)
* 9x GPIO/ADC/PWM

How to use the GPIO/ADC/PWM pins depends on the firmware. If you are using the default AP\_Periph - see [#ap\_periph-default-shipped-firmware](#ap_periph-default-shipped-firmware "mention"). If you are using Arduino DroneCAN - see [CAN Ecosystem](/docs/can-ecosystem.md#arduino-dronecan)

<figure><img src="https://1239082692-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FdPR57GIwyNGpujTZHIUm%2Fuploads%2FvGgxGPauPiZZNHgoRgAQ%2Fimage.png?alt=media&amp;token=fae12c8f-3f43-4d49-8d36-d557a0f80e11" alt=""><figcaption></figcaption></figure>

## Programming the board

### ST-Link

STM32 allows the ability to easily debug programs over SWDIO. This allows live variable inspection, breakpoints and more - which makes program development much easier!

The "STLINKV3" header is directly compatible with the [STLINK-V3MINIE](https://www.st.com/en/development-tools/stlink-v3minie.html). To upload code to the CAN Node, simply:

1. Connect the node to the STLINKV3
2. Click upload or debug in VS-Code!

The pins on the ST-LINK header could also be used with normal Arduino jumpers so a STLINKV2, or another SWD based debugger could be used. The pins are as follows:

<figure><img src="https://1239082692-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FdPR57GIwyNGpujTZHIUm%2Fuploads%2FPL3MPytGuF9zuHRXex45%2Fimage.png?alt=media&amp;token=8d65b019-97a8-45a8-a854-3fc46b811c3b" alt=""><figcaption><p>STLINK Header</p></figcaption></figure>

<table><thead><tr><th width="246">Pin Number</th><th>Description</th></tr></thead><tbody><tr><td>1</td><td><mark style="color:orange;">NC</mark></td></tr><tr><td>2</td><td><mark style="color:orange;">NC</mark></td></tr><tr><td>3</td><td>5V in</td></tr><tr><td>4</td><td>SWD</td></tr><tr><td>5</td><td><mark style="color:blue;">GND</mark></td></tr><tr><td>6</td><td>SWC</td></tr><tr><td>7</td><td><mark style="color:blue;">GND</mark></td></tr><tr><td>8</td><td><mark style="color:orange;">NC</mark></td></tr><tr><td>9</td><td><mark style="color:orange;">NC</mark></td></tr><tr><td>10</td><td><mark style="color:blue;">GND</mark></td></tr><tr><td>11</td><td><mark style="color:orange;">NC</mark></td></tr><tr><td>12</td><td><mark style="color:orange;">NC</mark></td></tr><tr><td>13</td><td>UART2_TX</td></tr><tr><td>14</td><td>UART2_RX</td></tr></tbody></table>