Before getting started, I thought it would be helpful to explain the features of the scary cat and and provide an overview of how it works. When first powering up the cat, its eyes will fade in and out for a short time before the servo motor resets the head position to face the front. The PIR sensor on the base of the unit then monitors for infrared movement/changes. When the sensor is triggered, the cat's head will move side to side, while the LED eyes slowly fade in and out. Concurrently, the ISD1820 sound record module will playback whatever sound was previously recorded. The cat has a built-in speaker and electret microphone. I simplified ISD1820 functions, such as recording and playback, by wire a couple of switches and the microphone to the enclosure. I programmed the scary cat using the Arduino IDE and decided to use an an ATtiny84 microcontroller instead of a full-blown Arduino. The circuit includes an ICSP programming header for users to modify/improve the code and upload it directly to the cat with the appropriate programmer. Finally, I included a TP4056 charging module to use a 3.7V rechargeable LiPO battery. The cutout in the base of the unit permits the charging LED to be monitored instead of having to remove the cover. That about sums it up!