Holiday cards that blink and beep have always fascinated us. This is our hackable DIY version made with an ATtiny13A and a few LEDs - push the button to play a short light show in the tree. We're sending these to friends and family this year. It's a handmade, hackable gift, and it was a ton of fun to build. This instructable explains our design, then you can grab the open source files and build your own.
You can buy a copy of our card at Seeed Studio. Assembled cards are ($15), and a kit for adventurous solderers is $12.
You can also see this article with the original formatting at DangerousPrototypes.com.
Step 1: Hardware - ATtiny13A
A small ATMEL ATtiny13A microcontroller (IC1) is the brain of the circuit. One pin (PWM) blinks the lights, most of the other pins are used for programming and power. You could get similar effects with a 555 timer or discrete components, but our goal is to learn about a new microcontroller family and make something easy to hack.
The ATtiny needs a 10K pull-up resistor (R1) to hold the reset pin high, a mini tactile switch (S1) resets the ATtiny by temporarily connecting the reset pin to ground. A 0.1uF capacitor (C1) decouples the chip from the power supply.
Step 2: Hardware - Programming and battery
ATtiny microcontrollers are programmed through a six-pin In System Programming (ISP) connection. The ISP header is oriented towards the back of the card. We made a programming probe to avoid soldering a pin header on the board.
Power is supplied by a 3volt, 20mm lithium coin cell (BAT1) on the back of the PCB. The holder should work with 2025 or 2032 coin cells. The ATtiny will work over a range of voltages, down to 1.8volts.