AVR PC Beeper

Replace boring POST beep with Imperial March or Morrowind theme!

Features

• 2 boards with integrated speaker, which play selected tune on boot
• 4 modes (controlled by 2 switches):
  • (0b00) - passthrough, POST beep is played as-is
  • (0b01) - Star Wars Imperial March
  • (0b10) - Morrowind theme (aka Nerevar Rising / Call of Magic)
  • (0b11) - Russian anthem
• Adjustable volume (blue potentiometer)

Hardware

To detect POST signal AVR microcontroller reads motherboard speaker ground pin -SP. I've created 2 devices in different form factors. Both are based on ATtiny85 microcontroller (simply because I had these lying around, you may use a different one).

Schematic for both boards is mostly the same (mini-ITX board doesn't have SW3 switch):

PCI board

Large board which plugs directly into PCI port. Has an external panel, which exposes 2 toggle switches (SW1 and SW2) and a potentiometer shaft (P1). Note that when installed, back panel may be flipped. To select passthrough/tune correctly, orient the panel so that volume shaft is the left side.

This board also has a dedicated dip switch (SW3) which disables POST trigger. When this dip switch is ON, avr doesn't read motherboard speaker pin (-SP). Instead, it plays selected tune once after being powered. This means the tune may be played after waking from sleep mode. This dip switch is ignored when passthrough is selected.

Mini-ITX board

Tiny board, suitable for mini-ITX builds where space is at premium. Tune/passthrough is selected with 2 on-board dip switches (SW1 and SW2). Unlike PCI build, there is no dip switch to disable POST trigger (SW3). The board must be manually connected to a 5v power source with wires.

Pin order (top-down, board is positioned so that pins are on the left side):

1. +5V - power source, you can use speaker+ pin on the motherboard
2. -SP - trigger pin, connects to speaker- pin on the motherboard
3. gnd - you can use ground pin from any free port on the motherboard

Known issue: when volume is set above ~90%, the board may start playing satanic screeches or otherwise behave strangely.

Software

How to build

Install required packages:

• avr-gcc
• avr-libc
• avrdude

Run make to build .hex file.

How to flash

You can use any AVR ISP programmer supported by avrdude. I am using Arduino as ISP, to use other programmer modify PROGR variable in Makefile.

Connect the programmer and run make flash PORT=<usbport> to upload .hex file to AVR. You may need superuser privileges, for example when using Windows Subsystem for Linux:

sudo make flash PORT=/dev/ttyS3

Revisions

• rev. 2 (current)
• rev. 1 - first 2 boards, see corresponding branch