Circuit Playground is chock-full of blinkies, sensors and electronic goodies. Since there's a lot going on, we're going to look at each piece one by one and talk about what it is and how to use it. This is a technically-oriented description for the Developer Edition and the people who are planning on writing code for Circuit Playground
All 8 non-power pads around the circuit playground have the ability to act as capacitive touch pads. Each pad has a 1Mohm resistor between it and digital pin #30. You can toggle this pin to control whether the resistor is a pullup or pulldown or floating. Note that this means that all the pads have a 2Mohm resistance between them.
You can also of course just use those pads for GPIO, we expose the hardware Serial (TX + RX), hardware I2C (SDA + SCL) and 4 gpio pins that can also do analog readings. They are the same exact pins as those on the Flora
Each Circuit Playground comes with 10 'NeoPixels' (technically, SK6812-3535 chips). These are connected to digital pin #17 and are powered by the 3.3V regulator. This is technically undervolting but we test them at this voltage and they work fine, if slightly tinted
There are three tactile pushbutton switches. One is the Reset button. Press this button once to reset, double-click to enter the bootloader manually.
The other two buttons are the Left and Right buttons, connected to digital #4 (Left) and #19 (Right) each. These have pull-down resistors installed so are, by default, LOW and when pressed read HIGH. This is to make if-then logic a little easier to read for beginners
There is a single slide switch near the center of the Circuit Playground. It is connected to digital #21 and will read LOW when slid to the left, and HIGH when in the right hand position
There is an analog light sensor, part number ALS-PT19, in the top left part of the board. This can be used to detect ambient light, with similar spectral response to the human eye.
This sensor is connect to analog pin #A5 and will read between 0 and 1023 with higher values corresponding to higher light levels. A reading of about 300 is common for most indoor light levels.
There is an NTC thermistor (Murata NCP15XH103F03RC) that we use for temperature sensing. While it isn't an all-in-one temperature sensor, with linear output, it's easy to calculate the temperature based on the analog voltage on analog pin #A0. There's a 10K resistor connected to it as a pull down.
You can make your circuit playground sing with the built in buzzer. This is a miniature magnetic speaker connected to digital pin #5 with a transistor driver. You can use PWM at varying frequencies to make basic tones.
A MEMS microphone can be used to detect audio levels and even perform basic FFT functions. You can read the analog voltage corresponding to the audio on analog pin #A4. Note that this is the raw analog audio waveform! When it's silent there will be a reading of ~330 and when loud the audio will read between 0 and 800 or so. Averaging and smoothing must be done to convert this to sound-pressure-level.
A LIS3DH 3-axis XYZ accelerometer is in the dead center of the board and you can use it to detect tilt, gravity, motion, as well as 'tap' and 'double tap' strikes on the board. The LIS3DH is connected to the hardware SPI pins (to leave the I2C pins free) and has the CS pin on digital pin #8 and an optional interrupt output on digital pin #7 (also known as IRQ #4)