# Note-arduino and ESP32 serial with custom pins

**URL:** <https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438>\
**Category:** Uncategorized\
**Created:** [November 8, 2024, 2:57am UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438 "2024-11-08T02:57:40Z")\
**Posts on this page:** 13\
**Page:** 1

<div class="post-metadata">

**Author:** ![devElert](https://avatars.discourse-cdn.com/v4/letter/d/8e8cbc/32.png) [@devElert](https://discuss.blues.com/u/devElert)\
**Post date:** [November 8, 2024, 2:57am UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/1 "2024-11-08T02:57:40Z")

</div>

We recently had to switch our project from using I2C to using serial for communicating with the Notecard.

Naturally, I anticipated this would be pretty straightforward, but unfortunately that was far from the experience I got.

The ESP32 family offers flexible pin assignments to peripherals, such as the UARTs, allowing peripherals to be used with almost any choice of IO pins. Our choice was guided by the available pins, whether they can be controlled by the uLP processor and other hardware constraints.

`note-arduino` tries to own the `Serial` instance, calling `Serial.begin()`/`Serial.end()` and then `Serial.begin()`. This happens during the call to `Notecard.begin()` where the serial connection is reset.

This obviously works fine when the default pins are used, but not when custom pins are used.

HardwareSerial on ESP32 has a `setPins()` method which allows the developer to override the default pins. Unfortunately, this configuration is cleared when `HardwareSerial.end()` is called, resulting in the default pins being used rather than the pins intended.

The workaround is to create a subclass of `NoteSerial` that handles the serial port, with knowledge of how to correctly set it up.

```auto
class NoteSerialConfig : public NoteSerial {
    unsigned rxPin;
    unsigned txPin;
    HardwareSerial& serial;
public:
    NoteSerialConfig(HardwareSerial& hw) : serial(hw), rxPin(-1), txPin(-1) {}

    void setPins(unsigned rxPin, unsigned txPin) {
        this->rxPin = rxPin;
        this->txPin = txPin;
    }

    bool begin() {
        serial.begin(9600, SERIAL_8N1, rxPin, txPin);
        return true;
    }

        / ************************************************************************** /
    /*!
        @brief Determines if the Notecard Serial port has data available.
        @return The number of bytes available to read.
    */
    / ************************************************************************** /
    virtual size_t available(void) {
        return serial.available();
    }

    / ************************************************************************** /
    /*!
        @brief Read a byte from the Notecard Serial port.
        @return A single character byte.
    */
    / ************************************************************************** /
    virtual char receive(void) {
        return serial.read();
    }

    / ************************************************************************** /
    /*!
        @brief Resets the serial port.
        @return `true` if the Serial port is available.
    */
    / ************************************************************************** /
    virtual bool reset(void) {
        serial.end();
        return begin();
    }

    / ************************************************************************** /
    /*!
        @brief Writes a message to the Notecard Serial port.
        @param buffer
                  The bytes to write.
        @param size
                  The number of bytes to write.
        @param flush
                  Use `true` to flush to Serial.
        @return The number of bytes transmitted.
    */
    / ************************************************************************** /
    virtual size_t transmit(uint8_t * buffer, size_t size, bool flush) {
        size_t result = serial.write(buffer, size);
        if (flush) {
            serial.flush();
        }
        return result;
    }
};

```

Unfortunately this is mostly boilerplate code, since `NoteSerial_Arduino` is a final class and can’t be extended. If it weren’t final, only the begin() method would need to be overridden.

You can use a global instance of this if `Notecard.end()` is not called, or allocate one dynamically, when `Notecard.end()` is used, which attempts to deallocate the instance.

```auto
// globals
HardwareSerial notecard_serial(1);   
NoteSerialConfig noteSerialConfig(notecard_serial);
Notecard notecard;

```

During `setup()`, we can then set up the pins for the serial connection, and pass it to Notecard:

```auto
    noteSerialConfig.setPins(PIN_NOTECARD_RX, PIN_NOTECARD_TX);
    notecard.begin(&noteSerialConfig);

```

Ideally `note-arduino` would be a little more friendly with non-default serial settings, but for anyone who’s struggling with this, I hope this workaround helps.

---

<div class="post-metadata">

**Author:** ![zfields](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.blues.com/zfields/32/29_2.png) [@zfields](https://discuss.blues.com/u/zfields)\
**Post date:** [November 8, 2024, 1:46pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/2 "2024-11-08T13:46:18Z")

</div>

Hi @devElert ,

The problem comes from the ESP32’s not standard `Serial::begin()` implementation.

`note-arduino` passes a callback to `note-c` that relies on the `Serial::begin()` and `Serial::end()` functions to properly reset the Serial peripheral.

A better description and solution are provided in the following post:

> [@Note-arduino library: could you add Rx, Tx pin options to Notecard.begin()](https://discuss.blues.com/t/note-arduino-library-could-you-add-rx-tx-pin-options-to-notecard-begin/2344/15):
>
> Hi @mark_pdx, Thanks for sharing that. Yes, that is part of my problem. I have the ESP32-S3-WROOM-1-N8R2, configured as a ESP32-S3-DevKitC-1. The chip itself is equivalent to the Adafruit Feather ESP32-S3 2MB PSRAM, but the pins are routed differently on the ESP32-S3-DevKitC-1 than they are on the Feather and the board is not behaving correctly as a result. I’m curious something similar is causing your attempt at using SoftwareSerial to manifest as a runtime error. I will purchase a the Ada…

Please have a look, and see if it will suit your needs.

Best,  
Zak

---

<div class="post-metadata">

**Author:** ![zfields](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.blues.com/zfields/32/29_2.png) [@zfields](https://discuss.blues.com/u/zfields)\
**Post date:** [November 8, 2024, 3:03pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/3 "2024-11-08T15:03:43Z")

</div>

Hi again @devElert,

We were workshopping a workaround, and we decided it would be best for you to temporarily eliminate the Reset callback in your application by using the following strategy:

```cpp
extern serialResetFn hookSerialReset;
hookSerialReset = NULL;

```

Then as an official solution in the next release of `note-arduino` (coming soon), we are going to update `note-c` and `note-arduino` to have “getter” functions for the callbacks.

This would allow you to do something similar to the following…

```cpp
serialTransmitFn transmit;
serialAvailableFn available;
serialReceiveFn receive;

NoteGetFnSerial(NULL, &transmit, &available, &receive);
NoteSetFnSerial(NULL, transmit, available, receive);

```

You could pass in `NULL` as the reset callback (shown above), or implement a custom reset callback that manages your custom pin selection.

Cheers,  
Zak

---

<div class="post-metadata">

**Author:** ![zfields](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.blues.com/zfields/32/29_2.png) [@zfields](https://discuss.blues.com/u/zfields)\
**Post date:** [February 25, 2025, 5:27pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/4 "2025-02-25T17:27:03Z")

</div>

To follow up, `note-arduino` has now been updated to support the syntax shown above.

`note-arduino` version 1.6.4 will be available from the Arduino Library Manager shortly.

---

<div class="post-metadata">

**Author:** ![devElert](https://avatars.discourse-cdn.com/v4/letter/d/8e8cbc/32.png) [@devElert](https://discuss.blues.com/u/devElert)\
**Post date:** [April 7, 2025, 11:01pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/5 "2025-04-07T23:01:35Z")

</div>

I tried using this in with the 1.6.6 release, but unfortunately wasn’t able to get it to work.

```auto
   HardwareSerial notecard_serial(1);

setup() { 
...
    // set up the GPIOs to use for UART1. These are remembered until end() is called.
   notecard_serial.setPins(boardPins.PIN_NOTECARD_TX_P, boardPins.PIN_NOTECARD_RX_P);
    

    serialTransmitFn transmit;
    serialAvailableFn available;
    serialReceiveFn receive;
    // get the original serial functions, and clear the reset function so that the configuration of the UART isn't overitten.
    NoteGetFnSerial(NULL, &transmit, &available, &receive);
    NoteSetFnSerial(NULL, transmit, available, receive);
    notecard.begin(notecard_serial);

```

During `notecard.begin()` the serial hooks are reset to their default values, including the reset function.

```auto
void Notecard::begin(NoteSerial * noteSerial_)
{
    noteSerial = noteSerial_;
    platformInit(noteSerial);
    if (noteSerial) {
        NoteSetFnSerial(noteSerialReset, noteSerialTransmit, // <--- here
                        noteSerialAvailable, noteSerialReceive);

        // Set the default debug serial throttling
        J *req = NoteNewRequest("card.aux.serial");

```

---

<div class="post-metadata">

**Author:** ![devElert](https://avatars.discourse-cdn.com/v4/letter/d/8e8cbc/32.png) [@devElert](https://discuss.blues.com/u/devElert)\
**Post date:** [April 9, 2025, 11:35pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/6 "2025-04-09T23:35:17Z")

</div>

Btw, I’m not in a hurry to get a fix for this - I’m happy to continue using a subclass of NoteSerial (code in the first post) that handles begin() and end() as needed.

---

<div class="post-metadata">

**Author:** ![zfields](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.blues.com/zfields/32/29_2.png) [@zfields](https://discuss.blues.com/u/zfields)\
**Post date:** [April 14, 2025, 8:22pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/7 "2025-04-14T20:22:11Z")

</div>

Ah, yes. I see the problem.

To create a proper solution, it will take both changes to `note-c` and `note-arduino`.

I will get to work on that and report back.

Thanks for bringing this up!  
Zak

---

<div class="post-metadata">

**Author:** ![JakobStruebing](https://avatars.discourse-cdn.com/v4/letter/j/8edcca/32.png) [@JakobStruebing](https://discuss.blues.com/u/JakobStruebing)\
**Post date:** [September 10, 2025, 1:57pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/8 "2025-09-10T13:57:08Z")

</div>

Any Update on this? I am facing the same issue and im wondering if i should wait for a change in the library or attempt one of the fixes people did

---

<div class="post-metadata">

**Author:** ![zfields](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.blues.com/zfields/32/29_2.png) [@zfields](https://discuss.blues.com/u/zfields)\
**Post date:** [September 18, 2025, 3:42pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/9 "2025-09-18T15:42:10Z")

</div>

Hello @JakobStruebing ,

Welcome to the Blues forum! I’m so sorry I missed your question.

Yes and no, we did update `note-c` and I attempted to update `note-arduino`, but I missed an important piece. I will push an update out shortly.

In the interim, you should be able to call `Notecard::begin()` before you update the callbacks, and that would ensure your preference is saved. In the next release, the order will no longer matter.

Happy hacking,

Zak

---

<div class="post-metadata">

**Author:** ![zfields](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.blues.com/zfields/32/29_2.png) [@zfields](https://discuss.blues.com/u/zfields)\
**Post date:** [September 24, 2025, 12:47pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/10 "2025-09-24T12:47:04Z")

</div>

Hello all,

I’ve released a new version of `note-arduino`, and now `Notecard::begin()` should no longer reset any callbacks you’ve supplied directly.

Be sure to let me know if this doesn’t resolve your issue.

~Zak

---

<div class="post-metadata">

**Author:** ![devElert](https://avatars.discourse-cdn.com/v4/letter/d/8e8cbc/32.png) [@devElert](https://discuss.blues.com/u/devElert)\
**Post date:** [October 1, 2025, 4:46am UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/11 "2025-10-01T04:46:56Z")

</div>

I understand what you say, but that is some rather dense language. Could you please share an example that’s been tested on the ESP family of chips?

---

<div class="post-metadata">

**Author:** ![zfields](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.blues.com/zfields/32/29_2.png) [@zfields](https://discuss.blues.com/u/zfields)\
**Post date:** [October 1, 2025, 1:42pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/12 "2025-10-01T13:42:12Z")

</div>

Hello @devElert ,

I finally slowed down and looked at the example you provided above.

```cpp
setup() { 
...
    // set up the GPIOs to use for UART1. These are remembered until end() is called.
   notecard_serial.setPins(boardPins.PIN_NOTECARD_TX_P, boardPins.PIN_NOTECARD_RX_P);
    

    serialTransmitFn transmit;
    serialAvailableFn available;
    serialReceiveFn receive;
    // get the original serial functions, and clear the reset function so that the configuration of the UART isn't overitten.
    NoteGetFnSerial(NULL, &transmit, &available, &receive);
    NoteSetFnSerial(NULL, transmit, available, receive);
    notecard.begin(notecard_serial);

```

I completely overlooked that the current behavior of `Notecard::begin()` will set all `NULL` values to the default serial callbacks. So in your case, you would want to call `Notecard::begin()` before your calls to `NoteGetFnSerial()` and `NoteSetFnSerial()`.

```cpp
    notecard.begin(notecard_serial);
    NoteGetFnSerial(NULL, &transmit, &available, &receive);
    NoteSetFnSerial(NULL, transmit, available, receive);

```

This would allow the default values to be set, then you would immediately unset them. I expect this will solve your problem.

A better solution yet is to initialize the callbacks to an invalid pointer, instead of `NULL`. Then I will be able to differentiate unset pointers from a pointer deliberately set to `NULL`, as in your case.

---

<div class="post-metadata">

**Author:** ![devElert](https://avatars.discourse-cdn.com/v4/letter/d/8e8cbc/32.png) [@devElert](https://discuss.blues.com/u/devElert)\
**Post date:** [January 20, 2026, 9:04pm UTC](https://discuss.blues.com/t/note-arduino-and-esp32-serial-with-custom-pins/2438/13 "2026-01-20T21:04:28Z")

</div>

Hi Zak,

Circling back to this after testing note-arduino 1.8.2. It’s working well, with no need for the custom code I posted at the start of the thread. 🎉

We do supply a reset function so that the UART can be re-initialized when needed by note-c, with the pins correctly set.

Thanks for implementing this!