# AVR-HF ADX-MI3

> Pre-built digital mode QRP transceiver for amateur radio, supporting FT8, FT4, JS8, and WSPR on HF bands from 160m to 6m with ~5W output, OLED display, and single USB-C cable operation.

## Quick Facts

- **Brand:** JasonKits QRP
- **Board Type:** transceiver
- **Price:** ~$70
- **Product Readiness:** consumer
- **CPU:** AVR 8-bit single-core @ 16MHz
- **CPU Architecture:** AVR 8-bit
- **CPU Cores:** 1
- **RAM:** 2KB SRAM
- **Flash:** 32KB
- **USB:** USB-C (gold-plated, integrated hub)
- **Power:** 12V DC input with PTC fuse protection
- **Operating Voltage:** 5V
- **Operating Temp:** -40°C to +85°C
- **Antenna:** SMA
- **Display:** 0.91" OLED 128×32

## Open Source

- **Firmware:** Yes
- **Schematics:** Yes
- **PCB Layout:** Yes

## Compatible Firmware

arduino

## Use Cases

- amateur-radio
- digital-mode-hf
- qrp-portable-operation
- off-grid-communication
- rf-experimentation

## Components

- **ATmega328P** (mcu): Atmel ATmega328P 8-bit AVR RISC MCU running at 16MHz with 32KB flash, 2KB SRAM, and 1KB EEPROM. Controls all transceiver functions including frequency synthesis, band selection, OLED display, and CAT serial communication. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fww1.microchip.com%2Fdownloads%2Fen%2FDeviceDoc%2FAtmel-7810-Automotive-Microcontrollers-ATmega328P_Datasheet.pdf&ref=openhardware.directory&product=avr-hf-adx-mi3&source=md-export)
- **CD2003GP** (hf-receiver): Single-chip FM/AM radio receiver IC used as the front-end receiver for HF signal reception. Provides the receive signal path in this QRP transceiver design. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fgithub.com%2FWB2CBA%2FADX%2Fblob%2Fmain%2FCD2003.pdf&ref=openhardware.directory&product=avr-hf-adx-mi3&source=md-export)
- **Si5351** (clock-generator): Silicon Labs Si5351 I2C-programmable clock generator used as the variable frequency oscillator (VFO) for both transmit and receive frequency synthesis across all supported HF bands. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fwww.skyworksinc.com%2F-%2Fmedia%2FSkyworks%2FSL%2Fdocuments%2Fpublic%2Fdata-sheets%2FSi5351-B.pdf&ref=openhardware.directory&product=avr-hf-adx-mi3&source=md-export)
- **SSD1306** (display-driver): Solomon Systech SSD1306 OLED display controller driving a 128×32 pixel monochrome OLED screen for frequency display, band information, and operating mode status. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fcdn-shop.adafruit.com%2Fdatasheets%2FSSD1306.pdf&ref=openhardware.directory&product=avr-hf-adx-mi3&source=md-export)

## Protocols

- **I2C** (I2C): SDA: A4, SCL: A5
- **UART** (UART0): RX: PD0, TX: PD1
- **USB** (USB-C): USB-C connector (integrated hub with sound card and serial adapter)

## GPIO Map

| Pin | Name | Type | Functions |
|-----|------|------|-----------|
| PD0 | UART RX (CAT control) | UART | digital-input, digital-output |
| PD1 | UART TX (CAT control) | UART | digital-input, digital-output |
| PD2 | Band ID 3 | Digital | digital-input, digital-output |
| PD3 | Band ID 1 | Digital | digital-input, digital-output, pwm |
| PD4 | UI Pushbutton | Digital | digital-input, digital-output |
| PD5 | TX LED | Digital | digital-input, digital-output, pwm |
| PD7 | Analog Comparator | Analog | digital-input, digital-output |
| PB0 | RX Gate | Digital | digital-input, digital-output |
| PB1 | Band ID 2 | Digital | digital-input, digital-output, pwm |
| PB2 | Band ID 0 | Digital | digital-input, digital-output, pwm |
| ADC6 | Battery Voltage Monitor | Analog | adc |

## Description

## Overview

The AVR-HF ADX-MI3 is a compact, pre-built digital mode QRP transceiver designed for licensed amateur radio operators. Based on the open-source ADX (Arduino Digital Transceiver) platform originally designed by WB2CBA and enhanced by Scott Baker KJ7NLA, the MI3 represents the third iteration of the ADX-MINI family with significant improvements over its predecessors.

The transceiver supports FT8, FT4, JS8Call, and WSPR digital modes across HF bands from 160 meters to 6 meters using pluggable low-pass filter modules for band selection. It delivers approximately 5 watts of RF output on the 20-meter band and ships pre-built and air-tested with a 20-meter filter module installed. Additional band filter modules are available separately.

What sets the ADX-MI3 apart from earlier versions is its integrated design that combines a USB hub, USB sound card, and USB serial adapter for CAT control into a single USB-C connection. This means the entire station — audio in, audio out, and rig control — runs through one cable to the host computer running WSJT-X or similar software. The 128x32 OLED display replaces the LED indicators of the MI2, providing a cleaner user interface with one-button operation and a dedicated Tune Mode.

The hardware is built around an ATmega328P microcontroller, a CD2003GP receiver chip for the front end, and a Si5351 programmable clock generator for frequency synthesis. The Class-E RF amplifier topology keeps the design simple and efficient. The firmware is open source under the MIT license and can be modified using the Arduino IDE, making this an excellent platform for amateur radio experimentation and learning.

## Where to Buy

- [Tindie](https://openhardware.directory/r?to=https%3A%2F%2Fwww.tindie.com%2Fproducts%2Fjasonkits_qrp%2Favr-hf-adx-mi3-digital-mode-qrp-trx%2F&ref=openhardware.directory&product=avr-hf-adx-mi3&source=md-export) — $70.00

## Resources

- [product](https://openhardware.directory/r?to=https%3A%2F%2Fwww.tindie.com%2Fproducts%2Fjasonkits_qrp%2Favr-hf-adx-mi3-digital-mode-qrp-trx%2F&ref=openhardware.directory&product=avr-hf-adx-mi3&source=md-export)
- [github](https://openhardware.directory/r?to=https%3A%2F%2Fgithub.com%2Fscottlbaker%2FADX-MINI&ref=openhardware.directory&product=avr-hf-adx-mi3&source=md-export)
- [schematics](https://openhardware.directory/r?to=https%3A%2F%2Fgithub.com%2Fscottlbaker%2FADX-MINI%2Ftree%2Fmaster%2Fhardware%2FMI3%2Frev1.3%2Fgerbers&ref=openhardware.directory&product=avr-hf-adx-mi3&source=md-export)

## Tags

`qrp`, `amateur-radio`, `ham-radio`, `ft8`, `wspr`, `hf-transceiver`, `digital-modes`, `arduino`, `atmega328p`, `open-source`

## Images

![AVR-HF ADX-MI3](https://nbg1.your-objectstorage.com/openhardware-directory/entities/avr-hf-adx-mi3/e256548fad83.jpg)
![AVR-HF ADX-MI3](https://nbg1.your-objectstorage.com/openhardware-directory/entities/avr-hf-adx-mi3/11d280f06250.jpg)

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