# Circuit Playground Classic > All-in-one ATmega32u4 learning board with 10 NeoPixels, LIS3DH accelerometer, microphone, speaker, light and temperature sensors, and 8 capacitive touch pads in a circular 2-inch form factor. ## Quick Facts - **Brand:** Adafruit - **Board Type:** dev-board - **Price:** ~$19.95 - **Product Readiness:** developer - **CPU:** ATmega32u4 @ 8 MHz - **CPU Architecture:** AVR 8-bit - **CPU Cores:** 1 - **RAM:** 2.5KB SRAM - **Flash:** 32KB - **Power:** 5V via Micro-USB / AAA battery pack / 3.7V LiPo - **Operating Voltage:** 3.3V - **Dimensions:** 50.6mm diameter - **Weight:** 8.5g - **Antenna:** none ## Open Source - **Firmware:** Yes - **Schematics:** Yes - **PCB Layout:** Yes ## Compatible Firmware arduino ## Use Cases - educational-platform - wearable - prototyping - stem-education ## Components - **ATmega32u4** (mcu): 8-bit AVR microcontroller at 8MHz, 3.3V with native USB, 32KB flash, 2.5KB SRAM. — [Datasheet](https://openhardware.directory/r?to=http%3A%2F%2Fwww.atmel.com%2FImages%2FAtmel-7766-8-bit-AVR-ATmega16U4-32U4_Datasheet.pdf&ref=openhardware.directory&product=circuit-playground-classic&source=md-export) - **LIS3DH** (accelerometer): ST triple-axis MEMS accelerometer with tap detection and free-fall detection. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fwww.st.com%2Fresource%2Fen%2Fdatasheet%2Flis3dh.pdf&ref=openhardware.directory&product=circuit-playground-classic&source=md-export) - **SPW2430HR5H-B** (microphone): MEMS microphone for sound sensing and audio input. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fcdn-learn.adafruit.com%2Fassets%2Fassets%2F000%2F040%2F891%2Foriginal%2FSPW2430HR5H-B.pdf&ref=openhardware.directory&product=circuit-playground-classic&source=md-export) - **NCP15XH103F03RC** (thermistor): NTC thermistor for ambient temperature measurement. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fcdn-learn.adafruit.com%2Fassets%2Fassets%2F000%2F040%2F892%2Foriginal%2FNCP15XH103F03RC.pdf&ref=openhardware.directory&product=circuit-playground-classic&source=md-export) ## Protocols - **I2C**: SDA: D2, SCL: D3 - **UART**: TX: D1, RX: D0 - **SPI**: MOSI: D16, MISO: D14, SCK: D15 - **USB HID**: ## GPIO Map | Pin | Name | Type | Functions | |-----|------|------|-----------| | D0 | RX — UART Receive / Capacitive Touch | UART | digital-input, digital-output | | D1 | TX — UART Transmit / Capacitive Touch | UART | digital-input, digital-output | | D2 | SDA — I2C Data | I2C | digital-input, digital-output | | D3 | SCL — I2C Clock | I2C | digital-input, digital-output | | D16 | SPI MOSI | SPI | digital-input, digital-output | | D14 | SPI MISO | SPI | digital-input, digital-output | | D15 | SPI SCK | SPI | digital-input, digital-output | | D15 | A0 — Analog In / DAC / Capacitive Touch / PWM | — | analog-input, analog-output, digital-input, digital-output, pwm | | D4 | A1 — Analog In / Capacitive Touch / PWM | — | analog-input, digital-input, digital-output, pwm | | D5 | A2 — Analog In / Capacitive Touch / PWM | — | analog-input, digital-input, digital-output, pwm | | D12 | A3 — Analog In / Capacitive Touch / PWM | — | analog-input, digital-input, digital-output, pwm | | D24 | A4/SDA — Analog In / I2C SDA / Capacitive Touch | I2C | analog-input, digital-input, digital-output | | D25 | A5/SCL — Analog In / I2C SCL / Capacitive Touch | I2C | analog-input, digital-input, digital-output | ## Description ## Overview The Circuit Playground Classic is Adafruit's all-in-one educational microcontroller board built around the ATmega32u4 running at 8 MHz and 3.3V. It packs an astonishing array of hardware into a circular 2-inch (50.6mm) board designed to be worn, clipped, and coded by beginners and experts alike. The board features 10 mini NeoPixel RGB LEDs arranged in a ring, a LIS3DH triple-axis accelerometer with tap and free-fall detection, a MEMS microphone, a mini magnetic speaker, a phototransistor for light sensing, an NTC thermistor for temperature, and two push buttons plus a slide switch — all without needing any wiring. All eight I/O pads around the perimeter are alligator-clip friendly and support capacitive touch input, making it ideal for craft and wearable projects. The pads also offer analog input, PWM output, and hardware I2C and UART for connecting external sensors and modules. The Circuit Playground Classic is programmable via Arduino IDE and works with Adafruit's CircuitPlayground library, providing easy access to all onboard sensors. It was designed as the original version of the Circuit Playground platform before the Express model introduced CircuitPython support. ## Where to Buy - [Adafruit](https://openhardware.directory/r?to=https%3A%2F%2Fwww.adafruit.com%2Fproduct%2F3000&ref=openhardware.directory&product=circuit-playground-classic&source=md-export) — 19.95 ## Resources - [product](https://openhardware.directory/r?to=https%3A%2F%2Fwww.adafruit.com%2Fproduct%2F3000&ref=openhardware.directory&product=circuit-playground-classic&source=md-export) - [github](https://openhardware.directory/r?to=https%3A%2F%2Fgithub.com%2Fadafruit%2FAdafruit-Circuit-Playground-PCB&ref=openhardware.directory&product=circuit-playground-classic&source=md-export) - [wiki](https://openhardware.directory/r?to=https%3A%2F%2Flearn.adafruit.com%2Fintroducing-circuit-playground%2Foverview&ref=openhardware.directory&product=circuit-playground-classic&source=md-export) - [datasheet](https://openhardware.directory/r?to=http%3A%2F%2Fwww.atmel.com%2FImages%2FAtmel-7766-8-bit-AVR-ATmega16U4-32U4_Datasheet.pdf&ref=openhardware.directory&product=circuit-playground-classic&source=md-export) - [schematics](https://openhardware.directory/r?to=https%3A%2F%2Fcdn-learn.adafruit.com%2Fassets%2Fassets%2F000%2F031%2F914%2Fmedium800%2Fcircuit_playground_schem.png&ref=openhardware.directory&product=circuit-playground-classic&source=md-export) ## Tags `circuit-playground`, `atmega32u4`, `neopixel`, `educational`, `capacitive-touch`, `accelerometer`, `wearable`, `adafruit` ## Images ![Circuit Playground Classic](https://nbg1.your-objectstorage.com/openhardware-directory/entities/circuit-playground-classic/42b5ea0c5486.jpg) --- [View full device page](https://openhardware.directory/devices/circuit-playground-classic)