Mrmoddom: Created MuTag project page with features, repository structure, usage, and contact info.

2025-05-07T12:03:37Z

Created MuTag project page with features, repository structure, usage, and contact info.

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{{Project
|Picture=Mutag v2 1.jpg
|Project Status=Finished
|Participants=Mrmoddom
}}
== MuTag v2.1 ==
The first MuHack's NFC keychain!

This is a custom PCB with the ATTiny44a microcontroller and an ST25 NFC ISO15 tag.

From the microcontroller, you can access the NFC tag via I²C, modify its configuration, and read/write data.

== Features ==
* '''MCU''': ATTiny44a
* '''NFC Tag''': ST25 NFC ISO15 (4 Kbit memory)
* '''Energy harvesting'''
* '''High-speed Mailbox''': 256 bytes
* '''4 LEDs''' in different colors
* '''Dimensions''': 20 × 60 mm

== Getting Started ==
In the Hardware folder, you'll find the PCB design files and electrical schematics.

<pre>
#define YELLOW_LED 0
#define GREEN_LED 1
#define BLUE_LED 2
#define RED_LED 3
</pre>

The LEDs are connected to:
* Yellow → PA0
* Green → PA1
* Blue → PA2
* Red → PA3

The NFC tag is on the I²C bus of the ATTiny:
* SDA → PA6
* SCL → PA4

The tag's GPO pin is connected to INT0 of the ATTiny (PB2).

=== Activating Energy Harvesting Mode ===
By default, the tag is in "on demand" mode. To set it to permanent energy harvesting mode:
# Install the ST25 NFC app from the Play Store: https://play.google.com/store/apps/details?id=com.st.st25nfc
# Scan the tag and go to "Register Management"
# Read the tag again; locate the register `EH_MODE` (0x01 = on demand)
# Set `EH_MODE` to 0x00 and press "Save" (default password = 0000)

== Programming the ATTiny44a ==
An external ISP programmer is required: we will use an Arduino Uno as the programmer.

# Upload the `ArduinoISP` sketch to the Arduino.
# Add this URL to the "Additional Boards Manager URLs" in the Arduino IDE preferences:
<pre>http://drazzy.com/package_drazzy.com_index.json</pre>
# Install "ATTinyCore" by Spence Konde and select:
{| class="wikitable"
|+ Settings
|-
! Option !! Value
|-
| Board || ATTiny24/44/84 (noBootloader)
|-
| Chip || ATTiny44(a) (v2.0 → select 24)
|-
| Clock || 1 MHz internal
|-
| BOD || Disabled
|-
| LTO || Enabled
|-
| EEPROM || Retained
|-
| millis()/micros() || Enabled
|-
| Programmer || Arduino as ISP
|}
# MuTag ↔ Arduino connections:
{| class="wikitable"
|-
! MuTag !! Arduino
|-
| VDD || 5 V
|-
| GND || GND
|-
| SCK || 13
|-
| MISO || 12
|-
| MOSI || 11
|-
| RST || 10
|}
*Note:* The through-hole pads on the MuTag are now 2.54 mm.

To start flashing, touch GND with the Arduino's reset pin a few seconds before hitting "Upload" in the IDE (or use "Upload using Programmer").

== Accessing the NFC tag via I²C ==
The internal memory of the ST25 tag is mapped as an I²C EEPROM at address `0x53`.
Example sketch: `Hello_MuHack.ino`.

== TODO ==
* Add 3D model of the PCB
* Find a bootloader for UART programming
* Evaluate removing the diodes
* Enlarge programming pads
* Change MCU to ATTiny44/84 (more memory)
* Remove the `RESET` pad

== Bootloader Notes ==
The Optiboot bootloader (Spence Konde) uses the AIN0/AIN1 pins (connected to the LEDs). Options:
* Remove the LEDs to use the pins for UART
* Recompile the bootloader with different pins

This project is designed as a keychain (single programming), so the LEDs were kept and the bootloader was not invested in.

== License ==
Copyright © 2023 MrMoDDoM
This project is licensed under the GNU Affero General Public License (AGPL-3.0).
See [[LICENSE.md]] for details.

== Links ==
* Project page on GitHub: https://github.com/MrMoDDoM/MuTag
* Google Play ST25 NFC App: https://play.google.com/store/apps/details?id=com.st.st25nfc

MuTag - Revision history

Mrmoddom: Created MuTag project page with features, repository structure, usage, and contact info.