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.
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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
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On Tue, 27 Jun 2006 14:45:53 +0100, Conor

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.
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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.
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Jon D wrote:

snip...
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.
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John McGaw
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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?
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wrote:

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.
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wrote:
<snip>

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

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.
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On Wed, 28 Jun 2006 11:59:17 +0100, Jon D wrote:

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
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wrote:

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.
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--- 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.
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wrote:

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.
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Jon D wrote:

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