For easy programming and serial communication, the board integrates a CH340B USB-to-serial converter, allowing direct connection to any USB-equipped computer without the need for external adapters. The Challenger T3217 comes pre-programmed with the Optiboot bootloader, enabling convenient firmware upload and rapid iteration directly over USB.

In addition, the board features a dedicated Li-Po battery connector and onboard charger circuit, allowing the Challenger T3217 to operate as a fully portable platform. When connected via USB Type-C, the integrated charger automatically manages battery charging while powering the system. This makes the board ideal for battery-driven embedded applications, portable sensors, and low-power IoT devices.

True to the design principles of the Challenger platform, the T3217 features a clean and minimalistic layout with high-quality components and a robust power design. Whether you are exploring low-power control systems, building automation projects, or developing compact IoT devices, the Challenger T3217 provides a dependable foundation with excellent electrical performance and expandability.

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Key Features

• Microcontroller: Microchip ATtiny3217 (8-bit AVR® core, 20 MHz internal oscillator)
• Memory: 32 KB Flash / 2 KB SRAM / 256 B EEPROM
• I/O: All 20 I/O pins fully accessible via Challenger+ header connectors
• Interfaces: 1× USART, 1× SPI, 1× I²C, 10-bit ADC, 8-bit DAC, timers, comparator, event system
• USB Connectivity: USB Type-C interface with CH340B USB 2.0 to UART transceiver
• Bootloader: Pre-installed Optiboot for firmware upload via USB
• Battery Support: Built-in Li-Po charger and 2-pin battery 1.25mm pitch connector for portable operation
• Operating Voltage: 3.3 V logic level (USB or Li-Po powered)
• Form Factor: Challenger+ standard (compatible with Challenger accessories and expansion boards)
• Dimensions: 50.8 mm × 22.86 mm (Feather-compatible outline)
• Weight: ≈ 9 g

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Short introduction to the board

PCB
The Challenger+ board format is based on a popular form factor called “Feather” created and maintained by an American company called Adafruit. The entire specification for the Feather format is available here. The size of the PCB for the module is 50.80mm x 22.86mm but the entire module is a little bit bigger as the Type C USB connector protrudes about 1 mm outside the board. The Challenger+ uses another much smaller battery connector to allow the board to be integrated in more confined spaces.

Headers
On each of the longer sides of the PCB there are holes intended for soldering pin header connectors. If you don’t want to use connectors for some reason you can also solder a wire directly into the hole, making a permanent connection to your external device. If you go this way please make sure that the wires are fixed in place, otherwise vibrations can cause the wire to brake at the soldering point.

BConnect
The BConnect interface is a compact 4-pin connector designed by iLabs to provide a simple and reliable link between the Challenger+ board and compatible expansion modules. It carries power, ground, and UART/I2C communication signals, allowing for both data transfer and power delivery through a single flat flex cable. The connector uses a low-profile design to ensure secure and correct insertion, making it ideal for compact or embedded applications.

The Challenger T3217 board implements both a sink and the source connector which allows you to operate it both as a BConnect I2C master and a I2C slave. Using SoftwareSerial you can of course also implement connections to BSerial compatible modules.

LED’s
On each side of the USB connector there is a small indicator LED placed. The LED which is marked CHG is the charge control indicator. This red LED will shine whenever the connected battery is being charged, and when the battery is fully charged the LED will turn off again. If you haven’t connected a battery to the board this LED will not come on at all.

On the other side of the USB connector there is a user programmable green LED. This LED is connected to pin PIN_PA6 and can easily be controlled by the user program.

Hardware details

Challenger Header Pin Mapping (ATtiny3217)

The Challenger headers expose selected GPIO, communication interfaces, power, and reference signals from the onboard ATtiny3217 microcontroller. Pin naming follows the Arduino-style convention where applicable.

Digital I/O Pins

Header Name	MCU Pin	Mapped ATtiny3217 Function	Description
D5	PC4	GPIO	General-purpose digital I/O
D6	PC5	GPIO	General-purpose digital I/O
D9	PB4	GPIO	General-purpose digital I/O
D10	PB5	GPIO	General-purpose digital I/O
D11	PB6	GPIO	General-purpose digital I/O
D12	PB7	GPIO	General-purpose digital I/O
D13	PA7	GPIO	General-purpose digital I/O

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Analog / GPIO Pins

Note: A5 is not usable as analog input on this board due to internal connections.

Header Name	MCU Pin	Mapped ATtiny3217 Function	Description
A0	PA0	AIN0 / GPIO	Analog input or digital I/O
A1	PA1	AIN1 / GPIO	Analog input or digital I/O
A2	PA2	AIN2 / GPIO	Analog input or digital I/O
A3	PA3	AIN3 / GPIO	Analog input or digital I/O
A4	PA4	AIN4 / GPIO	Analog input or digital I/O
VREF	PA5	VREFA / GPIO	Analog reference input

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Serial Interfaces

Header Name	MCU Pin	Mapped Function	Description
TX	PB2	USART TX	UART transmit
RX	PB3	USART RX	UART receive
SCK	PC0	SPI SCK	SPI clock
SDI	PC1	SPI MOSI	SPI master out
SDO	PC2	SPI MISO	SPI master in
SDA	PB1	TWI SDA	I²C data
SCL	PB0	TWI SCL	I²C clock

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ATtiny3217 pin function table

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Power and Control Pins

Header Name	Connection	Description
+3V3	Regulated rail	3.3 V output from onboard LDO
VBUS	USB input	USB supply voltage
VBAT	Battery input	Li-ion / LiPo battery voltage
GND	Ground	System ground
EN / RESET	PA0 / RESET	External reset / enable
UPDI	PA0	Programming / debugging interface

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Summary Notes

• All header pins are directly connected to the ATtiny3217 unless otherwise noted.
• Level translation is used on USB-UART paths; headers are 3.3 V logic only.
• The pinout is compatible with Challenger ecosystem headers, but functionality depends on firmware configuration.
• External peripherals must not drive pins beyond VDD + 0.3 V.
• The UPDI functionality is disabled on shipped units and the GPIO/Analog functionality is enabled.

Hardware Overview

Power System

The Challenger T3217 can be powered either through the USB Type-C connector or from a connected single-cell Li-Po battery. The power system automatically switches between USB and battery operation, ensuring seamless transitions without user intervention.

A high-efficiency linear charger circuit manages the charging of the connected Li-Po cell whenever USB power is present. The charge current is factory-set to provide safe and reliable charging for small- to medium-capacity batteries commonly used in embedded and IoT applications. A built-in status indicator LED provides visual feedback during charging and full-charge states.

The board operates entirely at 3.3 V, with both the ATtiny3217 and peripheral circuits powered from the regulated system rail. USB 5 V input is routed only to the charger and voltage regulator section, protecting the MCU and I/O pins from overvoltage.

USB Interface

The integrated CH340B USB-to-UART converter provides a reliable communication bridge between the ATtiny3217’s serial interface and the host computer. It supports standard baud rates up to 2 Mbit/s and enables direct programming and serial console access over a single USB Type-C connection.

When connected to a computer, the board enumerates as a standard serial (COM) port compatible with Windows, macOS, and Linux systems. The preloaded Optiboot bootloader allows firmware updates directly via USB without requiring external programmers or adapters, streamlining development and debugging.

Battery Connector

A standard 2-pin JST-PH connector provides connection for a single-cell Li-Po battery. The battery voltage is continuously monitored by the on-board charger circuit, which manages charge and discharge cycles automatically. The system can be operated solely from the battery, or from USB while charging.

I/O Headers

All microcontroller I/O pins are routed to the dual Challenger+ header connectors, providing full access to every digital and analog function of the ATtiny3217. Each header is clearly labeled for quick identification of GPIO numbers and peripheral assignments.

The pinout follows the Challenger+ standard, ensuring compatibility with a wide range of existing Challenger accessories, shields, and expansion boards. This makes the Challenger T3217 an ideal platform for modular development and rapid prototyping.

RESET

The reset on this board is a little bit different from other micro controller boards in our lineup. The reset line on the header pin connector and the reset button is tied to the enable pin on the LDO that is supplying the 3.3V to the board. This means that every HW reset cycle will be a “Power On” reset and with a complete clear of the RAM contents. If you need to have something survive between resets it means that you will have to store it in EEPROM.

Indicators

• Charge LED (CHG): Illuminates during battery charging; turns off when charging is complete.
• User LED: Connected to a general-purpose I/O (PIN_PA6) pin for application use.

Power down/sleep modes

The ATTiny3217 microcontroller features several sleep modes designed to minimize power consumption when full operation is not required. These modes allow flexible control of system power, enabling battery-powered applications to extend operating time significantly.

In the Idle mode, the CPU clock is stopped while peripherals such as timers, communication interfaces, and the event system remain active. This mode offers a quick wake-up time and is ideal when continuous peripheral operation is needed.

In Standby mode, the main system clock is halted, but selected asynchronous peripherals—such as the Real-Time Counter (RTC) and event system—can continue running. This mode strikes a balance between low power consumption and functional availability, and is well suited for periodic wake-up tasks.

The Power-Down mode provides the lowest current consumption by shutting down all system clocks. Only external interrupts, the watchdog timer, or the RTC can wake the device from this state. This mode is typically used when the application remains inactive for extended periods or during deep-sleep cycles in battery-powered systems.

Wake-up from any sleep mode restores normal operation within a few microseconds. The sleep control is fully managed in software through the CPU’s SLPCTRL register, allowing developers to dynamically select the most efficient mode at runtime.

Mode	Conditions (per datasheet)	Measured on Challenger T3217 board @ ~25 °C	Typical MCU @ 25 °C	Max MCU @ 25 °C	Notes
Idle	System clock = OSCULP32K (32.768 kHz)	38 uA (UART and RTC running)	2.9 µA	15 µA	CPU halted, peripherals clocked; current depends strongly on clock/peripherals.
Standby (RTC on, ext crystal)	RTC @ 1.024 kHz from XOSC32K (CL=7.5 pF)		0.69 µA	—	Lowest standby with external 32 kHz crystal driving RTC.
Standby (RTC on, internal ULP)	RTC @ 1.024 kHz from OSCULP32K	3.7 uA	0.71 µA	3.0 µA	Internal 32 kHz RC; also specified up to 6 µA (85 °C) / 8 µA (125 °C).
Power-Down	All peripherals stopped	2.5 uA	0.10 µA	2.0 µA	Same as Standby when everything is stopped; also 5 µA (85 °C) / 7 µA (125 °C).

Microcontroller Specifications — ATtiny3217

Parameter	Specification	Notes
Core	8-bit AVR® CPU (tinyAVR 1-Series)	Based on AVR® core with improved peripheral interconnect
Operating Frequency	Up to 20 MHz (internal oscillator)	No external crystal required
Flash Memory	32 KB	Non-volatile program memory
SRAM	2 KB	Volatile working memory
EEPROM	256 bytes	Non-volatile data storage
I/O Pins	Up to 22 programmable I/O pins	All routed to Challenger+ headers
Operating Voltage Range	1.8 V – 5.5 V	Board fixed at 3.3 V logic
ADC	10-bit, up to 150 ksps	Up to 8 analog channels depending on package
DAC	8-bit, single-channel	Buffered output, routable to pin
Analog Comparator	1 comparator with flexible input mux
Timers/Counters	3 × 16-bit TCA/TCB	One TCA (with PWM) + two TCBs
USART Interfaces	1 × USART (can operate as UART, LIN, or RS-485)	Used by Optiboot and CH340B. Can be used by the applications when the USB cable is disconnected.
SPI Interface	1 × SPI (master/slave)	Alternate pin configuration
I²C Interface	1 × TWI (I²C compatible)
Event System	Yes (up to 8 channels)	Peripheral interconnect without CPU load
Configurable Custom Logic (CCL)	2 lookup-table units (LUTs)	For simple hardware logic functions
Watchdog Timer	1 × WDT with windowed mode
Brown-out Detection (BOD)	Programmable thresholds
Clock Sources	20 MHz oscillator, 32.768 kHz RTC oscillator	External 32 kHz crystal optional
Real-Time Counter (RTC)	Independent low-power 16-bit counter	Supports wake-up from sleep
Sleep Modes	Idle, Standby, Power-Down	Optimized for low-power operation
Typical Active Current	≈ 2.5 mA @ 3.3 V, 1 MHz	From Microchip datasheet (typical)
Package Type	24-pin SOIC / 24-pin VQFN	Board uses 24-pin VQFN variant

Schematic