Problem with set_backlight(0) not reducing power

BikerRay

6

Problem with set_backlight(0) not reducing power

« on: 16 / June / 2011, 19:16:02 »

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I put a set_backlight 0 command in my motion detection script to cut back on power consumption on my A720IS. However, when I measure current drain, I get the following:
- camera in "Canon" mode, display off: 120ma
- camera in CHDK mode, display on: 450ma
- camera in CHDK mode, backlight off: 400ma
In the last mode, you can see the LCD is working, if you shine a bright light on it, just the backlight is off.
Any idea why the power consumption is so high with the backlight off? I was expecting close to 120ma.

Cheers,
Ray

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reyalp

14117

Re: Problem with set_backlight(0) not reducing power

« Reply #1 on: 16 / June / 2011, 21:35:39 »

The canon display off mode turns off a lot more stuff, including stuff (like the CCD and live view buffer) needed to do motion detection.

The backlight simply doesn't take very much power compared to the rest.

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BikerRay

6

Re: Problem with set_backlight(0) not reducing power

« Reply #2 on: 17 / June / 2011, 08:04:09 »

Thanks, that's what I surmised, but was surprised by how little power turning off the backlight saved. I think a lot of people are under the same misapprehension - which means turning off the backlight isn't worth the trouble (unless for other reasons). Back to lugging around the big battery, I guess! :-)

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reyalp

14117

Re: Problem with set_backlight(0) not reducing power

« Reply #3 on: 17 / June / 2011, 15:50:42 »

Quote from: BikerRay on 17 / June / 2011, 08:04:09

Thanks, that's what I surmised, but was surprised by how little power turning off the backlight saved. I think a lot of people are under the same misapprehension - which means turning off the backlight isn't worth the trouble (unless for other reasons).

Probably not, although a 10% percent is better than nothing.

MD is inherently power hungry, since it uses the CPU a lot and all the sensor hardware needs to be active all the time. Depending on your needs, slow MD (without keeping the shutter half pressed all the time) should probably be more power friendly.

Camera settings can also have a surprising influence, for example MF is takes measurably more power on most cameras.

Here's a thread with some measurements on a590: http://chdk.setepontos.com/index.php?topic=3872.0

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