BitCake – Electronic Birthday Cake
Features 9 LED candles that you can blow on, to make them flicker and go out, like you do with a real birthday cake! Each candle blinks with random period and phase that depends on the intensity of the air flow
Piezo sensor and a special air trap to detect air flow with astounding sensitivity using resonance effect
Atmel ATTiny44 microcontroller on board with 4 kilobytes of flash memory and 256 bytes RAM
Open source hardware and firmware. Can be re-programmed with an ICSP programmer or Arduino board via Arduino IDE
Size 42 x 42 x 18 mm, weight 26g
Powered by a single AAAA/LR61 battery (included)
3.3V step-up converter on board
Ultra low shutdown current (less than 1 ΅A in deep shutdown)
Hand-soldered using lead-free solder
The heart of the device is Atmel ATTiny44 microcontroller. Its built-in differential ADC channel with 20x gain is connected to a piezo sensor. The rest nine general input-output pins are connected to nine separate LEDs circuits.
A step-up DC-to-DC power converter is used to increase output voltage to 3.3V at the expense of increased current provided by the battery. For that purpose, Holtek 7733 integrated circuit is used. Its SOT-23-5 package has additional Chip Enable (CE) input that turns off the converter into deep shutdown with ultra-low supply current.
By pushing the button we open transistor to charge 10 ΅F capacitor that enables the step-up converter. At the same time a reset signal is sent to the microcontroller, so it starts to execute its program. The 10 ΅F capacitor slowly discharges via 10 MOhm resistor so that it will turn off the converter in 3 minutes.
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