Mike Rivers wrote:
On Jan 7, 10:00 am, Matt wrote:
I have one already that I've used in the past. It's a small 1GB Medion
MP3 player (MD80527 is the model number) that can record in 8 bit 32kb/
sec .wav format. It takes a single AAA battery.
This is where you'll need to find someone creative. Generally devices
that run off a single cell like that don't have provisions built in
for external power. I have a Raven MP3 player that looks like a USB
"thumb" memory drive and runs off a AAA battery. I can load and unload
files under USB power (without the battery) but it needs the battery
to play. If I wanted to run it from external power, I'd build a
"dummy" battery to fit the battery holder, make contact with the
springs at the ends, and attach leads to it to which I'd connect an
external battery with greater capacity.
I set it recording yesterday to test its battery life, and so far from
a fresh battery I've just gone past the 24 hour mark.
A D cell has 12 times the amp-hour capacity of a AAA, so you should be
able to power it for a week with a single D cell.
As someone pointed out, there may be a problem with the recorded file
growing to a greater size than the player (or even a computer's file
system) can handle. Most devices deal with this in one way or
another. Some just stop when the file reaches the maximum size, others
close that file, open a new one, and continue recording.
My recording I started going yesterday stopped a few minutes ago.
There was still enough battery life left to keep the screen going
(though would it stop if there wasn't enough to keep the recording
going?), and another 26 hours of memory remaining. Sadly it didn't
start a new file either. The file was just over 24 and a half hours
long, and is 336MB in size.
There is a lower quality setting (I think it's 8kb/sec) which I expect
should still be better then nothing, so I'll give that a try. I'm
assuming the restriction is likely to be on the size of the file,
rather then the length of the recording?
You should cobble something up with clip leads, a D cell, and maybe
some duct tape and see what happens when you let it record for three
days. Once you know how to make it work, you look for a craftsman to
make it look pretty. Or you can leave it with the clip leads and duct
tape, but be sure the people in the lecture room know it's not a
bomb. 
I take it the current from a D cell is the same as that from a AAA
since they are both 1.5V cells? I want to avoid any possible damage to
the MP3 player.
As an aside I've had a thought. By turning down the contrast on the
small LCD screen to as low as possible and making sure the backlight
doesn't come on for a brief few seconds at the start of the recording,
can I expect much of an improvement in battery life?
Kind Regards,
Matt