Two sound recorders to one speaker question.

The problem is likely because the low impedance output of the unuised
recorder is essentially shorting the speaker. One possible simple
solution (if you can tolerate a small volume degradation) is to put a
8-ohm resistor is series with each output. This will attenuate the
signal at the speaker (because of the divider from the in-use device,
and the 8-ohm shunt of the unused device), but should maintain the
audio fidelity.

 

If the (-) outputs of the recorders are isolated from one another, then
you could wire the two recorder outputs in series with each other.
Then connect the speaker across the combined output.

Mark

 

Hello,

I have a couple of 10sec sound recorder boards from toys that I wish
to connect to a single speaker. At the moment I have a breadboard with
a 16F84 PIC powering each board seperately via transistors before
triggering its PLAY connection, waiting a specified time period for
the sound to play then shutting it down. The problem is that the
boards have their own speaker connections running back to a gob-top
chip and if I have them both connected to an 8ohm 0.25 watt speaker
the playback sound is degraded. Connected seperately to the speaker
they're fine but with even only one wire from either of the other
boards speaker connections hooked up then the sound degrades powered
up or not.

The only way I can think of to solve this is a couple of PIC
controlled 5V DPDT relays, one for each pair of speaker wires. That
seems messy and though small the relays make an audiable click
especially when mounted.

Can anyone suggest another hopefully less complicated way to stop this
from happening?

Any help is always appreciated.

Cheers,

Andrew.

 

I would imagine that the audio preamp on the unit(s) has some AGC
(automatic gain control), so you probably aren't over-driving the input
too badly. If the audio playback is distorted or 'clipped', try
reducing the audio level from your soundcard. The only real potential
problems with this setup are the potential to overdrive (covered
above), or the detrimental affects of the electret mic bias on the
sound card output. But, since you said that it is working, I suspect
that the sound card output is ac coupled and rejects the mic bias. So,
if it isn't broken... ...don't fix it!

 

Thankyou both for replying.

I've tried the 8ohm resistor method and it worked well the audio being
much less garbled with a little drop in volume. I haven't yet tried
the other suggested method but I will at some point soon.

I'm entering the audio from mono WAV files from my computers soundcard
via a stereo cable and mono adapter to the electret mic (removed)
connections on the boards. Though it does work is there anything wrong
with this method or something I can do to improve it?

Cheers,

Andrew.

 

from those symptoms it sounds like the little chips have H-bridge output
stages, that means that opposite signals are tens out each speaker wire...

one DPDT relay would be enough

build your own from scratch ?

<http://www.atmel.com/dyn/resources/prod_documents/doc1456.pdf>

three ICs and a little other stuff (mostly resistors)...

you'll be able to recycle the microphone and speaker from your existing
setup

but I see you're using PICs - there may be something similar on the microchip
site.


Bye.
Jasen

 

Try putting a 1 k resistor in line with each sound recorder. This
worked for me. It does cut the volume a bit but the sound quality was
fine.

Pete

 

Once again thanks,

Andrew.