Current consumption of MP3 player with OLED display

I have an MP3 player and want to know its standalone current
consumption (when not plugged in to the USB port).

I used an inexpensive digital meter to measure the current
consumption value but I had three obvious problems and maybe some
less obvious ones. Is anyone able to get some more accurate figures
than mine?

FWIW the player is based on a SigmaTel 35XX chip.


----- MY READINGS (ALKALINE OR NiMH AAA CELL)

Switch on (by holding one button down): 150-200 mA.

No activity, fully bright OLED [dimmed]: 50 mA [25 mA]
Play voice recording, fully bright OLED [dimmed]: 75-85 mA [50 mA]
Play music recording, fully bright OLED: 85-90 mA
Record voice fully bright OLED [dimmed]: 95-100 mA [85-95 mA]


---- PROBLEMS AFFECTING MY READINGS

(problem 1) Unfortunately I saw the reading values "cycle" which
probably was in line with the poor sampling rate of my meter.

(problem 2) Also I found that that the player would actually switch
itself off as I changed functions which probably means my meter (in
series with the AAA cell) was not as unnoticed by the player as it
could have been.

(problem 3) The reading for microphone recording with dimmed display
looks rather suspect even though it was taken repeatedly.

 

OK. A point that you've not considered is that the values change up and
down in line with the volume of the music at that point. Take for
example a piece of classical music that is fairly low level volume then
comes to a very loud section. When the loud section starts, you'll see
the current draw increase. Not sure what cycling you saw but it would
be consistent with music that had a repetitive beat for example.


--
Conor
Sig under construction. Please check back when Duke Nukem Forever ships
and/or Windows Vista is released.

Cashback on online purchases:
http://www.TopCashBack.co.uk/Conor/ref/index.htm

 

Problem 3 doesn't really look like a problem. Don't forget that when you
are recording extra circuitry is switched on - the microphone amplifier,
and ADC. And, probably more importantly, if the unit is recording in MP3
or other compressed format then some relatively serious CPU power is
being expended in the encoding. I also believe that flash power
consumption is higher during writing that during reading.

But, what is it that you need "more accurate figures" for? I'm having a
hard time trying to figure out what purpose they could be put to.

 

That is quite possible, but not necessarily true. Consider
the typical op amp. Quiescent current remains static
regardless of the output, but it also means an inherant
limit on output potential but IIRC, on these portable
devices that is already artifically limited by some
regulations to prevent hearing loss.

In many modern players the output is integral to a
multifunction chip now, and OP would need pop open the
player or find someone who had to determine what the circuit
topology is.

 

Kony, you are right. The heavily modulated passages of music seemed
to make little difference to the readings I was getting.

Also, connecting headphones or having no headphones did not seem to
make any difference either.

Of course it could all be down to my rather basic digital multimeter
but I think I would have detected this sort of thing if it had been
there.

 

To take your first point, I tend to think that if the OLED display is
taking about 25 mA between full and dim then that 25 mA difference
should have been seen even when recording with a power consumption of
about 85 to 95 mA.

You ask about the need for more accuracy. I am not looking for "extra
decimal places" sort of accuracy but I want to check that my readings
are even in the right ball-park. My cheap digital meter is sampling
with a long interval and also its presence is affecting the operation of
the unit (as I mention in Problem-2).

Problem-2 should not be occurring and I suspect that current used in
driving the meter's circuit will be a cause of what I experienced. This
could mean I am over or under reading by quite a margin and might mean
that the readings are way out.

To me they all seem a bit on the high side.

Can anyone confirm such readings?

 

If you've got a 200 mv scale, measure the voltage across
a .1 ohm precision resistor in series with the battery.

Ed

 

Even if the unit is idle, if it is "on", parts of it must
be receiving power besides just the OLED display. Actually
every single chip is probably consuming a few uA but the
Sigmatel chip is probably consuming a few mA already.

Perhaps a more basic question, why do you need to know at
all, what the current is? You can arrive at a ballpark
figure if your battery is relatively new(er) and you merely
time how long it takes to run down in the state that matters
(the calculations would have to be applicable to your
intended use, right?). Keep in mind that the battery is
certainly powering a DC-DC boost circuit and it may cease
function around 0.7V (give or take, it'd be nice to have the
SigmaTel datasheet but it seems SigmaTel are being asses
about full disclosure of their chips' specs instead of just
openly linking them like anyone else typically does).

Anyway, even if your meter samples slow(er) than some, it
shouldn't be much of a problem, the current may actually be
fluctuating even if/when the average is somewhat constant.
To a certain extent this kind of momentary reading could be
expected with a switching converter, which I believe is
built into the SigmaTel 3500 series et al.

The current doesn't really drive the meter. The voltage
flows across a fixed, calibrated resistance inside the
meter, and the meter measures the voltage drop across that
internal load. End result is a marginally lower output than
input voltage, at least at this current range, going to the
player. It could be that when you change your meter
settings it is not providing the path across the resistance
shunt, the circuit is temporarily broken.

We don't even know what player you have. How long does it
claim to run on the battery and what battery (technology and
size) does it use? I have one player known to have a
SigmaTel 3500-something-or-other chip in it and it does use
somewhere in the neighborhood of 60mA, depending on whether
the display is lit or SRS/wow is on (I don't recall which
way it is about 60mA but probably without the display lit,
it's display is LCD and goes completely off/unlit, the
dimmer is only a manual setting change, otherwise it's
either lit or (usually) not lit.

If I can find that player I might fiddle with it and report
back.

 

Correction- above should read "... across that internal
resistance".

 

The MP3 player (by "Logik" = own-brand for UK high street chain)
switches off when I press functions ON THE PLAYER itself while the
meter is left untouched. It takes one AAA.

The switch off happens with:

(1) a new Duracell alkaline (1.52V with no load and a metered load of
150 mA sees voltage fall to 1.41V)

(2) Ever Ready Energizer NiMH (1.46V with no load and falling a
little on 150 mA - forget how much).

Howwever, if the NiMH is taken straight from the charger then it is
OK but even then, after a minute or so of button pressing on the MP3
player I see the player switches itself off. Shorting out the meter
from the circuit (it was measuring mA if you remember) makes it all
ok again and button pressing the MP3 player has no switch-off effect.

 

Does that also happen if you place an electrolitic capacitor over your
meter's leads. e.g 100 uF? Maybe the current drawn has high peaks which cause
large voltage drops fom you meter, and whichc you won't see.

Mat Nieuwenhoven

 

I've taken a few readings on what i believe to be a SigmaTel
3500 powered player (Sansa e130 with only integral memory,
memory card slot was empty).

It will not power on at all with the meter in series for
current measurements, I have a switch in parallel to the
meter to take the meter in and out of the circuit for
power-up.

Player off - current kept dropping, possibly as the lower
load on the battery resulted in it recovering from voltage
depression. I didn't measure the voltage though.

220 uA


Player on, scrolling a track title across screen but not
playing

27mA


Cycling back and forth from menus with backlight on

70mA


10 seconds after player sat idle from the menu navigations,,
scrolling a track title as above but with the backlight on.

48mA


Playing with backlight on, no load (no headphones plugged
in).

80mA


Playing with backlight off, no load.

58mA


Playing with backlight off, 32 Ohm headphones at full
volume.

58mA


Playing with backlight off, 32 Ohm headphones at lowest
volume.

58mA


Equalizer on and off, no change.

SRS Wow was off for all tests thus far.
SRS Turned on = roughly 86mA total (this figure fluctuated
more than the others), a 28mA increase


Fm radio playback

63mA

Player didn't have recording functionality implemented so no
readings for that.

 

--- snip --

Tremendous. That is great.

You're very helpful. Thank you very much for your efforts.

The display consumption your figures imply (22 mA) is like mine (25 mA).
Several other readings are a bit different but not another order of
magnitude. I don't have WOW/SRS (what a good iea to include it) so
maybe that is factors to take into account when comparing.

I am assuming that when you say "backlight on" that it equates to my
OLED being on and that when you say "backlight off" that it equates to
my OLED being dimmed.

This means that with a 900 mAh NiMH AAA cell that the device will stay
of for about up to a day or thereabouts with a lit display. (Depending
on the end-voltage it can work at). With the display dimmed, or in
power saving, this time is about a day and a half.

And for both devices playing time is probably 5 hours (900 mAh / 80 and
then taking only a half this value). Record time on mine would be a bit
less at approx 4 hours.

Like my results, the playing volume does not affect current consumption.

I too saw current dropping steadily and slowly at one point but not at
"off". I guessed (probably wildly) that it was the ebb of current out
of the memory chip.

Again I too saw a small current at "off" but I thought it was below the
resolution of my meter and I ignored it.

If (???) I have read the specifications correctly then flash memory uses
about 7 or 8 mA for something like 512 mA, si that probably isn't a
factor.

 

Mine has what I believe is a backlit LCD, not OLED. "Off"
means no light, only black characters visible on the
otherwise typical light greenish-grey, non-lit background.
"On" means the entire greenish-grey background is lit blue,
in appearance it seems to be an electroluminescent
backlight. There is a brighter/dimmer control for the
brightness of that, but I did not change that control for
the readings, it was probably around 75% brightness, then
there is a separate setting for a timer to turn off the
light altogether after it comes on automatically with
settings adjustments.

For the one I measured, I've heard reports of about 12 hours
runtime with the display mostly off, that is, coming on only
from occasional user input. I don't know if it was with the
SRS/Wow on or not. Personally I only use that with earbuds
which need it, and even then there is another equalizer
setting menu that does not increase power consumption (as
far as I could tell) that might be as desirable depending on
type of music. I'd never want SRS turned on with decent
full sized headphones, I'm somewhat of a purist in that
respect.

I think that is to be expected with most if not all of the
integrated output driver chips. Personally I'd prefer a
fairly biased class A/B discrete output which would effect
current consumption with volume, but it seems in the effort
to save 10 cents or 1 cu. cm of space they foregoe these
things on tiny players.

Mine retains presets for the FM tuner, a clock, possibly the
EQ and SRS settings too. I don't know how much of this is
saved to a config file, but certainly the clock would need
powered.

I don't know the resolution of your meter, if it has uA
current setting it may be believable but in only mA range,
there's a large margin for error, as would there be if it
were a cheap meter or had gone a long while without
calibration.

I would expect it depends on chip density, how many to make
512MB, IIRC mine has 1 chip but same player came with up to
2GB... I just didn't feel any need to go with a larger
integral capacity since it has the SD slot and supports
FAT32. I should have taken readings with a SD card in it
but didn't feel it would be directly applicable since you
didn't make mention of a card.