---
title: "Node UIO library"
space: "Node UIO"
url: "https://docs.modbee.org/node-uio/library"
updated: "2026-10-25"
---

# ModBee Node UIO board library

Board support for the ModBee Node UIO, an ESP32-S3 industrial I/O module for
35 mm DIN rail.

![ModBee Node UIO](/files/gitimg-3badb7c3b10c3feef69e0e638cb6bf4e74f6ed57.webp)

Hardware only: digital and analog I/O, pulse counting, the HAT power enable,
the button and status LED, Wi-Fi bring-up, sleep and wake, and the I2C
expansion bus. No communication protocol is built in. Modbus, the ModBee
protocol and anything else run alongside as their own libraries.

## The board

| | |
| --- | --- |
| Microcontroller | ESP32-S3FH4R2, up to 240 MHz, 4 MB flash, 2 MB PSRAM |
| Digital inputs | 8, 5-24 V DC, opto-isolated, two groups of four with separate commons |
| Digital outputs | 8, 5-24 V DC, opto-isolated high-side (sourcing) MOSFET; 100 mA per output from the board supply, 500 mA with a separate supply |
| Analog inputs | 4, ADS1115 16-bit; 0-20 mA as shipped, 0-10 V per channel by solder bridge |
| Analog outputs | 2, GP8413 15-bit; 0-10 V as shipped, 0-20 mA per channel by solder bridge |
| Serial | 2 x RS485 |
| Expansion | 2 x Grove I2C (3.3 V), two 8-pin stackable HAT headers |
| Power | 5-24 V DC. USB-C powers the logic only; the analog outputs need at least about 9 V |
| Mounting | 35 mm DIN rail, 118 x 58 x 45 mm |

Whether an analog channel measures or drives voltage or current is a solder
bridge, not a setting. [docs/HARDWARE.md](/node-uio/hardware) has the pinouts,
the GPIO map, the power rails and every solder bridge, all taken from the
[schematic](https://github.com/mod-bee/modbee-node-uio/blob/main/node-uio/schematics/modbee-node-uio.pdf).

## Using it

```cpp
#include <NodeUioAPI.h>

void setup() {
  uio().begin();
  uio().setInputRange(0, UIO_CURRENT);   // AI01 as shipped: 0-20 mA
  uio().setOutputRange(0, UIO_VOLTAGE);  // AO01 as shipped: 0-10 V
}

void loop() {
  uio().update();

  bool on = false;
  uio().digitalIn(0, on);
  uio().setDigitalOut(0, on);

  float milliamps = 0.0f;
  uio().analogIn(0, milliamps);
  uio().setAnalogOut(0, milliamps / 2.0f);   // 0-20 mA in, 0-10 V out
}
```

Everything goes through one class. [docs/API.md](/node-uio/api) is the
reference, and `examples/NodeUioBasic` is a complete sketch.

## With OpenPLC

The OpenPLC function blocks for this board live in
[modbee-openplc](https://github.com/mod-bee/modbee-openplc). They wrap this
library, so a program and a sketch see the same behaviour.

## Building

PlatformIO, from this directory, builds the example:

```bash
pio run -e lolin_s3_mini
```

To use the library in your own project, see
[Installing](/node-uio#installing) in the repository README.

## Layout

```
src/
  NodeUioAPI.{h,cpp}        the public interface
  NodeUioTypes.h            enumerations, limits and scaling
  NodeUioBoard.{h,cpp}      the driver behind it
  NodeUioExpansion.{h,cpp}  the I2C expansion module framework
  NodeUioPulse.h            pulse count to rate
  lib/                      vendored drivers: ADS1X15, GP8XXX
examples/  docs/  schematics/  images/
```

`src/` is the include root, so a vendored driver is reached as
`#include <lib/ADS1X15/ADS1X15.h>`.

## Licence

AGPL-3.0, see [LICENSE](https://github.com/mod-bee/modbee-node-uio/blob/main/node-uio/LICENSE). The vendored drivers keep their own MIT
licences, in their folders: ADS1X15 by Rob Tillaart, and GP8XXX, a modified
copy of DFRobot's DFRobot_GP8XXX.