Hardware Specifications

Microcontroller

Specification	Value
MCU	ATmega1284P
Clock	8 MHz (external crystal)
Flash	128 KB
SRAM	16 KB
EEPROM	4 KB
Core	AVR 8-bit

Radio Module

Specification	Value
Module	RFM95
Chipset	Semtech SX1276
Frequency	868 MHz (EU868)
Modulation	LoRa spread spectrum
TX Power	Up to 14 dBm
Interface	SPI

Pin Mappings

LoRa Radio (SPI)

Function	Arduino Pin	ATmega1284P Port
NSS (Chip Select)	24	PB0
RST (Reset)	25	PB1
DIO0	2	PD2
DIO1	3	PD3
DIO2	4	PD4
DIO3	0	PD0
DIO4	1	PD1
DIO5	26	PB2
MOSI	-	PB5 (hardware SPI)
MISO	-	PB6 (hardware SPI)
SCK	-	PB7 (hardware SPI)

Peripherals

Function	Arduino Pin	Description
PERIF_PWR	20	Peripheral power control
BUZZER	17	Buzzer output (analog pin 3)
JSN_TX	10	JSN sensor TX
JSN_RX	11	JSN sensor RX
ONE_WIRE	12	OneWire bus

I2C / SMBus

The I2C bus uses the hardware TWI interface:

• SDA: PC1 (hardware)
• SCL: PC0 (hardware)
• Bus Speed: 80 kHz

The sensor module is expected at address 0x36.

Debug Interface

Function	Description
UART TX	Debug output at 115200 baud
UART RX	Serial input

An FTDI-compatible 6-pin header provides debug access.

Fuse Settings

Fuse	Value	Description
lfuse	0xFF	External crystal, full swing oscillator
hfuse	0xD1	JTAG disabled, SPI enabled, BOD @ 2.7V
efuse	0xFF	Brown-out detection

Fuse Programming

Incorrect fuse settings can brick the device. Only modify fuses if you understand the implications.

Power

• Operating Voltage: 3.3V
• Brown-out Detection: 2.7V threshold
• Power Control: Pin 20 controls peripheral power

Programming Interface

Method	Tool	Speed
ISP	USBasp	0.25 MHz
ISP	Atmel ICE	Default

Upload command:

pio run -t upload

Upload flags used:

• -e : Chip erase before programming
• -B0.25 : Slow ISP clock (0.25 MHz)

Board Definition

The PlatformIO board definition is located at boards/mfm_v3_m1284p.json:

{
  "build": {
    "mcu": "atmega1284p",
    "f_cpu": "8000000L"
  },
  "frameworks": ["arduino"],
  "platform": "atmelavr"
}

Hardware Design Files

KiCad design files are available in the hardware/ directory:

• mfm-v3-smd.kicad_sch - Schematic
• mfm-v3-smd.kicad_pcb - PCB layout
• mfm-v3-smd.kicad_pro - Project file

Requires KiCad 6.0 or later.