Project: MinuteDuino

Fall 2016

The MinuteDuino is a small board that is designed to play music. Sounds are synthesized on an AtMega328, amplified with an LM386, and can be heard through the on-board speaker or on your headphones (through a 3.5mm jack). Below you can find images of the design, project schematic, and details about the fab. This design was based off of the PartyDuino, a 'noise-making' board designed in 2010 by a team of ECE students and M5; more at the project site .

Images

The bare PC board.

The assembled MinuteDuino.

Schematic.

Notes about the design

  • Audio Amp & Negative Supply IC: the Arduino produces a 5Vpp signal out of each audio pin. The current drive capabilities of the arduino are low, certainly not enough to drive an 8-ohm speaker so we want to amplify the audio signal. We perform the amplification with the popular LM386 audio amplifier (datasheet). The gain of this amplifier ranges from 26-46dB so we need to attenuate the input signal so that we don't experience any clipping at the output of the amp; this is the purpose of R102 and R103 (they form a voltage divider). Additionally, to get some more voltage swing at the output I supply pin 4 (the 'GND' pin) with -5V DC; I call this net 'VS'. Since this amplifier is a single supply device we have to play a trick for it to work properly. After the input ac-coupling capacitor, C104, we must connect all devices to our new GND net (VS) so that the circuit operates as if VS were GND. This effectively creates a 0-10V DC supply for the amplifier.
  • Board fabrication: the board was fabricated at PCB Zone in New Zealand (Circuit Labs actually prints the pc board; they are the same company). This company is great for super quick turn PCB at very low prices.
  • Power LED: 5mA current is quite bright.