Chiffchaff Card

Details

The chiffchaff is a very cute singing bird that is quite common in Hungary. I started this project because I really like the song of this bird and I wanted to create something in the "business card" form factor.

The heart of the build is the speaker which was salvaged from an old Nokia 3310 cellphone. It is driven by a single pin of the ATtiny45 through a low pass RC filter.

This microcontroller has only 4 kbytes of program space so it was a real challenge to fit the song of the bird in it. The original .wav file was first clipped, then encoded into a 1-bit bitstream with the "BTc Sound Encoder" software from Roman Black. Finally, the small pauses in the bird song were removed and it was splitted into 3 separate "chiff"-s for better storage.

The microcontroller is in deep sleep most of the time. It only wakes up when the button is pressed and it goes to sleep immediately after finishing the song.

The PCB was manufactured using a DIY UV exposure box.

Files

sound.h

header file containing the 1-bit bitstream sound

x-chdr - 15.96 kB - 12/30/2017 at 19:02

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main.c

source code

x-csrc - 1.78 kB - 12/30/2017 at 19:02

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chiff.hex

hex file for direct uploading

hex - 7.45 kB - 12/30/2017 at 19:02

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chiff.sch

eagle schematics

schematic - 246.63 kB - 12/30/2017 at 11:27

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chiff.brd

eagle board

board - 56.70 kB - 12/30/2017 at 11:27

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Components

1 × ATtiny45 Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers

1 × Nokia 3310 speaker

1 × CR2032 SMD holder

1 × Resistors: 10k and 6k8

1 × Capacitor: 0.22u

Build Instructions

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1

Manufacturing the PCB

When I design a layout in Eagle, I like to print it out on regular paper, to see the design in real life and to check the sapcing of the components. You can see a few versions here:
Then I printed the final design on transparent film.
This was the first time I used my selfmade UV exposure box, so in order to minimize the possibility of a failure, I used a single layer PCB which had preapplied photoresist.
Unfortunately I also switched chemicals and I didn't have a proper scale to measure the quantities so I had many-many failures before getting a decent board.
I used a chemical tinning solution to make the traces and the image of the bird shiny and corrosion resistant.
2
Populating the board
There's only two tricks in soldering the components:
1. There must be a wire connection between "PAD1" and "SPK2" underneath the speaker. (I didn't want to have two layers just for this connection)
2. The speaker is also connected using small pieces of wires. I found that using a silicon based glue makes a good, flexible fixation for the speaker.
3

Programming the board

Some wires with an ISP connector must be soldered to the top pads temporarly. You need to have the coin cell already installed during programming! After uploading the program and desoldering the wires the board is fully functional.
The microcontroller is always powered, but sleeping most of the time. It only wakes up when the button is pressed and it goes back to sleep immediately after the song is finished.