"Humorous Birthday Card" In-A-Box Hack
(January
2014)
I have been very
fond of the really funny audio greeting cards made by
'that greeting card company' featuring 'those cute funny
characters' for some time. A humorous card is nice,
but a humorous birthday card hacked in-a-box is a real
gift that keeps on giving! So I set out to make just
that - for my Dad's 70th.
First, I bought one
of those adorable funny audio cards from that greeting
card company's store. Then I tore it open and pulled
the electronics out that were glued to the back of the
card on the inside of a fold.
Next, I prepared a
heavy plastic food container that was of the right size to
contain a AAA battery holder, a pushbutton switch, the
speaker, and the audio PCB. I drilled holes in the
lid for the speaker and the pushbutton. This was
going to be sooooo easy.
Next I had to
remove the battery cover and switch that were on the PCB
and take out the CR2032 3V lithium battery that the
greeting card ran on so that I could hook up a more robust
set of replacable AAA batteries.
And here is where
it got interesting - because any attempts to power the
little potted chip with any kind of higher current 3VDC
source would fail to operate the chip. Using 2 AAA
lithium batteries at 3.5VDC just caused the speaker to
chirp. A little over-voltage, I thought.
Hooking it up to my variable bench supply I found that as
I slowly reduced the supply voltage from around 4VDC on
down that the audio output became longer and longer, and
it played more and more of the recording as the voltage
dropped. At around 2VDC It played the entire
message. It seems as though some kind of sensing
circuit on the input varies the total playback time of the
chip relative to the current supplied under load.
The RC clock seemed to remain at relatively the same speed
between 3VDC and 2VDC, based on the playback, but the time
it would run changed greatly. I found that any
change in impedance in the power supply, like dirty clip
leads to a battery or long leads, would effect whether it
played or not, how much of the message it played, and for
how long. (It may also be sensitive to the specific
capacitance of the CR2032 cell, hard to tell) I
speculated that this could have been engineered in as a
clever way to keep people from taking the board out of the
card and doing anything inappropriate with it, like
hooking it up to a larger capacity battery so that you
could play it forever. Like what I did.
I found that a new single lithium AAA battery had just
about the right supply voltage of around 1.8VDC to run the
humorous recording at a higher current capacity than the
3V lithium watch battery it came with.
[Whenever I placed
the CR2032 cell back in the round holder and pushed down
on it to contact the PCB it played normally. There
are no traces on the bottom side of the PCB, and I could
find no resistance in the battery holder or other obvious
things that could be involved. I tried this
same experiment with three identical PCBs with the same
results. Go figure.]
Then I used my glue
gun to secure the battery holder and speaker in the food
container, and I had to bypass the second slot in the
battery holder to use just the single AAA for this.
I wired the positive supply through the pushbutton and to
the PCB and it was done. Piece of cake!
Birthday cake, that is....
All done! Enjoy!
