🐭 stUART

by Francis Studios

Current version is v1.0 🟢

Release date : 2025.07 📅

❓ What is stUART?

Stuart is an i2c communication protocol, that uses 2 wires to interface between two circuits (CLK and DATA) and send 8 bit frames (similarly to UART) but this is a simplistic "very stupid" method for simple embedded applications.

This repository contains the C/C++ library implementation for microcontrollers or programmable chip(set)s.

⌨️ Usage

It starts with Arduino. Currently only arduino environment is supported by this library. In the future I plan to extend this for other MCUs and maybe FPGAs.

1. Clone this repo to your system (see clone option up above)
2. Copy the repository to Documents/Arduino/libraries/ folder (or wherever you installed your Arduino IDE)
3. Include it in your project #include <stuart.h>
4. Connect two uController devices together (currenly Arduino is supported) [Select two GPIO pins for CLOCK and DATA]
5. Check the example files below
6. Upload transmit and receive onto different devices
7. Have fun :)

🔌 API reference

1) 🏁 .begin()

void stUART::begin(int timeFrame, int CLOCK, int DATA);

This function must be used in the setup() section of your code. This should only be called once and accepts the timeFrame (milliseconds) and the CLOCK pin number and DATA pin number.

2) 📡 .transmit()

bool stUART::transmit(int message);

With this method you can transmit any number that can fit in an 8 bit frame (from 0x00 to 0xFF a.k.a. 0-256 in decimal)- for larger numbers my suggestion is to break it up to digits and transmit in a digit based, or two digit based system - whatever fits your needs.

This function returns a boolean depending on if the transmission procedure is ready to start. Here is an example:

if (stUART::transmit())
      stUART::transmit(message[i]);

If transmit returns with true, you can start transmitting your message

Here is the full transmit example: Let's imagine, that you want to transmit the large number of 1234 (decimal) over this protocol. First you have to splice it up to singe (or double) digits and create a list or array of it and transmit those single/double digits like shown

#include <stuart.h>

void setup() {
  stUART::begin(100, 6, 5);
}

void loop() {
  int message[4] = { 1, 2, 3, 4 };

  for (int i = 0; i < 4; i++) {
    if (stUART::transmit())
      stUART::transmit(message[i]);
  }
}

Example file: 📁 arduino_send.ino

2) 📶 .receive()

int stUART::receive();

This method returns an integer number transmitted via the 8bit frame.

The largest number you can fit in the 8bit frame is 0b11111111 which equals to 255 decimal (this shouldn't surprise you, basic computing knowledge) so this function returns 256 in any case where the frame is not ready yet. So you can check your transmission package state like so:

void loop() {
  int result = stUART::receive();
  if (result < 0xFF) Serial.println(result); //check if frame is ready
}

here is a recieve example:

#include <stuart.h>

void setup() {
  Serial.begin(9600);
  stUART::begin(100, 6, 5);
}

void loop() {
  int result = stUART::receive();
  if (result < 0xFF) Serial.println(result);
}

and the example file below:

Example file: 📁 arduino_receive.ino

Equivalent arduino project: 📁 reader.cpp

📁 Files

💭 Theoretical knowledge

In this section I'm attempting to explain how this communication protocol works

Preconception: I wanted a simple communication protocol that can simply transmit a few numbers between microcontrollers, and I'm using Attiny45 and that kinda stuff in this project, so we would like to keep the number of pins required to the minimum

• ⏰ CLOCK : the clock line is by default low unless someone wants to speak. If a member tries to speak up, it pulls the CLK line high for timeFrame x 5 ms then a clock pulse for every single data bit which can be high or low

• 💾 DATA : data is transmitted on the data line during every clock pulse which can be digital high or digital low. Data is organized into frames. A frame consists of the 5 timeFrame long call signal and 8 bits of data which is then converted into an integer.

• 🪟 TIME_FRAME : time frame is a delay time in milliseconds of how long a pulse should last. Choose this wisely, knowing the limitations of your target system.