Sound Box





Sound Box
trial assembly


A friend gave me the carcass of an old audio player with its two speakers intact. Beautifully made
by Chinese craftsmen, but with gaps where the control panels used to be. I filled the gaps by letting
in pieces of recycled fibre board and ordered some electronics bits.

It's going to be a black box with a single red button. Press the button and it will play a random sound,
gunfire, bombs, sirens, whatever. No on/off switch, the quiescent drain is typically one microamp,
which won't worry the coin cell battery too much.

I've ordered the Taiwan manufactured HK628 chip from would you believe Mishawaka Illinois.
Already arrived from Solihull are the connectors (outputs for led lights) and prototyping board.
Chip expected soon, then we can get it wired up and working.




Click to hear sounds


Hurrah! The chip has arrived from Taiwan so it's time to get on with some soldering.
Both chip and coin cell holder will fit on a small strip of veroboard, which can be mounted on
plastic pillars. I have found some transducers in my junk box so shall try those before
wasting the two speakers in the black box.



Chip and coin-cell on stripboard, and row of possible transducers

The transducers to be tried are: tiny piezo device, large piezo disc with autotransformer,
small moving coil speaker. 32 ohm half headphone. The tiny piezo and half headphone can
be driven directly from the chip outputs, the large piezo and speaker will require a buffer
transistor.

Test Result

All the micro speakers were found to be weak and feeble, whereas the sound from
black box with its full size speakers was healthy and strident. No contest, then!

The five leds were seen to light in rotation, doing four cycles in each sound burst.
Decided to mount these where they can be seen on the front of the box.



The inner workings



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