Programming & Connectors

This guide provides detailed information about programming the Multiflexmeter 3.7.0 board and explains all external connectors.

Programming Requirements

Required Hardware

To program the Multiflexmeter 3.7.0, you need:

Atmel-ICE (or compatible AVR ISP programmer)
- USBasp
- AVR Dragon
- Arduino as ISP
6-pin ISP cable (2x3 connector, 2.54mm pitch)
Power source (battery or external 3.3V supply)

Programming Connection

Connect your programmer to the J5 - ICSP Header on the board.

J5 - ICSP/ISP Programming Header

Location: Main board
Type: 2x3 pin header (male, 2.54mm pitch)
Purpose: In-System Programming for firmware upload

Pinout Diagram

  ┌─────────────┐
  │ 1  MISO  VCC  2 │
  │ 3  SCK   GND  4 │
  │ 5  RST   MOSI 6 │
  └─────────────┘

Pin Assignments

Pin	Signal	Direction	Description
1	MISO	←	Master In Slave Out (data from MCU to programmer)
2	VCC	→	+3.3V power (can power board from programmer)
3	SCK	→	Serial Clock (programming clock signal)
4	GND	-	Ground reference
5	RESET	→	MCU Reset (active low, pulled high on board)
6	MOSI	→	Master Out Slave In (data from programmer to MCU)

Connection to Atmel-ICE

The Atmel-ICE uses a standard 6-pin AVR ISP cable. Connect as follows:

Atmel-ICE          J5 Header
=========          =========
Pin 1 (MISO) ───── Pin 1 (MISO)
Pin 2 (VCC)  ───── Pin 2 (VCC)
Pin 3 (SCK)  ───── Pin 3 (SCK)
Pin 4 (MOSI) ───── Pin 6 (MOSI)
Pin 5 (RST)  ───── Pin 5 (RST)
Pin 6 (GND)  ───── Pin 4 (GND)

J4 - FTDI Debug Connector

Location: Main board
Type: 1x6 pin header (female socket, 2.54mm pitch)
Purpose: Serial UART debugging and monitoring

Pinout

Pin	Signal	Description
1	NC	No connection
2	TXD	UART Transmit from MCU (AVR_TX0)
3	RXD	UART Receive to MCU (AVR_RX0)
4	NC	No connection
5	NC	No connection
6	GND	Ground

FTDI Adapter Connection

Connect a standard FTDI USB-to-Serial adapter:

FTDI Adapter       J4 Header
============       =========
GND ────────────── Pin 6 (GND)
TXD ────────────── Pin 3 (RXD)  ← Cross connection
RXD ────────────── Pin 2 (TXD)  ← Cross connection
VCC ────────────── Leave disconnected

Serial Settings:

Baud Rate: 115200
Data Bits: 8
Parity: None
Stop Bits: 1
Flow Control: None

J3 - SMBus/I²C Connector

Location: Main board
Type: 2x3 pin header (male, 2.54mm pitch)
Purpose: External I²C/SMBus device connection

Pinout

  ┌─────────────┐
  │ 1  SCL  VCC  2 │
  │ 3  SDA  VCC  4 │
  │ 5  ALERT SCL 6 │
  └─────────────┘

Pin	Signal	Description
1	SCL	I²C Clock line
2	VCC	+3.3V Power output
3	SDA	I²C Data line
4	VCC	+3.3V Power output (duplicate)
5	SMBALERT	SMBus Alert signal (optional)
6	SCL	I²C Clock line (duplicate)

I²C Specifications:

Bus Speed: 80kHz (configured in firmware)
Pull-up Resistors: Onboard 4.7kΩ
Default Sensor Address: 0x36

J1 & J2 - Module Connectors

Location: Main board
Purpose: Sensor module expansion slots

J1 - Module Left (1x3 socket)

Pin	Signal	Description
1	SCL	I²C Clock
2	SDA	I²C Data
3	SMBALERT	SMBus Alert

J2 - Module Right (1x3 socket)

Pin	Signal	Description
1	VCC	+3.3V Power
2	SDA	I²C Data
3	SCL	I²C Clock

Programming Workflow

Step 1: Hardware Setup

Connect Atmel-ICE to your computer via USB
Connect the 6-pin ISP cable from Atmel-ICE to J5 on the board
Verify cable orientation (Pin 1 to Pin 1)
Power the board if not powering from programmer

Step 2: Configure Programmer

Set your programmer to 3.3V target voltage:

# Atmel-ICE automatically detects voltage from target board
# Verify with:
pio run -t upload --verbose

Step 3: Upload Firmware

Using PlatformIO:

# Build and upload
pio run -t upload

# Upload only (if already built)
pio run -t upload --target nobuild

Using AVRdude directly:

avrdude -p m1284p -c atmelice_isp -P usb -B 0.25 \
  -U flash:w:.pio/build/mfm_v3_m1284p/firmware.hex:i

Step 4: Program Fuses (First Time Only)

avrdude -p m1284p -c atmelice_isp -P usb \
  -U lfuse:w:0xFF:m \
  -U hfuse:w:0xD1:m \
  -U efuse:w:0xFF:m

Fuse Settings Explained:

LFUSE (0xFF): External crystal oscillator, no clock divide
HFUSE (0xD1): EEPROM preserved on chip erase, 2.7V brownout
EFUSE (0xFF): Brown-out detection enabled

Step 5: Verify Programming

Connect FTDI adapter to J4 and open serial monitor:

pio device monitor

You should see:

Build at: Oct 25 2025 00:13:00
Initializing...
EV_JOINING

Troubleshooting

Programming Issues

Problem: avrdude: initialization failed, rc=-1

Solution:

Check cable connections at J5
Verify programmer voltage is set to 3.3V
Ensure board is powered
Try slower programming speed: -B 2.0

Problem: avrdude: Expected signature for ATmega1284P is XX XX XX

Solution:

Wrong chip selected - verify -p m1284p in command
Check if board uses ATmega1284P (not 328P)
Verify oscillator is running (fuse settings)

Problem: Device not responding after fuse programming

Solution:

Fuses may have disabled external oscillator
Requires high-voltage parallel programmer to recover
Contact board manufacturer for recovery service

Serial Debug Issues

Problem: No output on serial monitor

Solution:

Verify FTDI connections (TX ↔ RX are crossed)
Check baud rate is set to 115200
Confirm firmware was compiled with debug output enabled
Verify GND connection between FTDI and board

Problem: Garbage characters on serial monitor

Solution:

Wrong baud rate - set to 115200
Check that board crystal is 16MHz as expected
Verify FTDI adapter is 3.3V compatible

Next Steps

Pin Mappings - Complete GPIO assignments
Hardware Specifications - Board technical details
Quick Start - Initial setup guide
Development Guide - Development workflow