Ambient Light Sensor? They Are Used In Laptops, Pdas...

[timofonic]

Hello.

What about including an ambient light sensor? It seems interesting as could help in screen viewing and saving power. They also are quite cheap and manufactured by tons of different companies (even ones dedicated to light bulbs like OSRAM).

QUOTE
By using ambient light measurement to control display-screen backlighting, the sensor helps reduce overall system power in portable equipment.


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Light sensors are among the simplest and cheapest sensors, allowing their inclusion into numerous consumer products ranging from night lights to cameras.


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Ambient-light sensors are included in laptops to adjust the screen's backlight to comfortable levels for the viewer. The range of the comfortable levels is dependent on the room's light..

Understandably, a screen's brightness needs to increase as the ambient light increases. What is less obvious is the need to decrease the brightness in lower-light conditions, both for comfortable viewing and to extend battery life.
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http://www.eetasia.com/ART_8800447857_480700_NT_b357cb4b.HTM
http://www.wipo.int/pctdb/en/wo.jsp?WO=200...mp;DISPLAY=DESC

Regards.

 

[JakeK]

Lol another thing timofonic? I think you regret missing the time when they really wanted peoples input into its design. I am not saying that they don't now but most of it is confirmed.

 

[timofonic]

Yes, I came late to the party

This kind of sensor are widely used in portable devices, avoid problems with TFT screens and optimize power consumption. They seems quite cheap so maybe it's a nice addition for having more power autonomy.

 

[Clad]

Probably much cheaper just to adjust brightness manually.

Come on, it's a 200 quids device, we don't need suchs things as rumble, light sensing, bluetooth, ect...

And it's very software-independant, maybe later when the overall components price will fall craigix will add that as part of a minor revision ? But now that the design is nearly finished, I think we all want to hold that piece of plastic in our hands before adding those gadget functions.

 

[Blah]

The sensor is like 20 cents or so. A small price to pay for increased battery life and better visibility IMHO.

 

[timofonic]

The sensor is like 20 cents or so. A small price to pay for increased battery life and better visibility IMHO.

Yes! Finally someone understands it

So what the developers of Pandora say about this?

 

[Dimacus]

You also need an ADC to convert the analog signal into a digital signal.
And it would probably mean more plastic details (a small transparent plastic bit to allow light flow to the sensor) and such things often mean higher production costs.

 

[Squidge]

I can see where it can be useful - I would try to increase the brightness when in a bright room or outside, but hardly ever remember to decrease when in a darker room unless it starts hurting my eyes. As long as there would a way to turn it off however for when I do want it brighter or darker.

 

[Tobriand]

I can see the point, but once more, it's one of those features that might be a bit of a hassle to get in at this stage in development. Certainly interesting for an MK2, though - unless, of course, the CPU inputs needed for it are already taken up with other things...

 

[Karel Jansens]

Personally, I con't care about ambient sensors, but just one warning: Don't make the same mistake the geniuses at Nokia made when they put a sensor in the N810. They found just about the only spot where the sensor would allways be covered by the user's thumb, thus rendering its usefulness to merely a tad over zero.

If the developers decide to put one in, they better think long and hard about where to stick it. Oh, and make sure it can be turned off by the user.

 

[timofonic]

You also need an ADC to convert the analog signal into a digital signal.
And it would probably mean more plastic details (a small transparent plastic bit to allow light flow to the sensor) and such things often mean higher production costs.

QUOTE

In laptop design, ambient-light sensors are typically placed next to the speakers where the case has an opening for light. These audio portals are commonly covered by a cross-hatch pattern to protect the speakers. Because of this protection, and because the light sensor is next to the speaker instead of on top of it, the light is obstructed. The obstruction reduces the amount of light available to be measured, thus requiring a solution with good low-light accuracy. For the accuracy needed in low-light conditions, the best sensor choice is the integrated photodiode with an ADC, Figure 4.

Figure 4: Block diagram of light-sensing system in a laptop.

The inclusion of a high-pass filter minimizes power supply noise from coupling into the backlight illumination.

Another common application is an ambient-light sensor used in a cellphone, where every mA-hour saved translates into longer battery life and happier customers. The enable/disable function is equally important for the battery-saving, power-down feature. The extension of battery life is remarkable. With the light sensor to adjust the backlight illumination, battery life is increased by at least a factor of 6, assuming the backlight remains on full power without feedback from a light sensor.

Figure 5 shows a complete automatic backlight control circuit for cellphones.

Figure 5: Automatic white-LED backlight intensity control circuit (Click to view full image).

 

[Chip]

Lets do a little cost-benefit analysis. What does it really cost to add an ambient light sensor?

There is the sensor itself, of course. There is the analog to digital converter that will convert it's output into a digital value. The most logical place for the sensor is in the lid, so you also need wires and connectors to get the signal from the sensor to the board.

What about system resource costs? How many levels of brightness do you want to sense? Even at 4 bit resolution, you need 4 lines into the CPU. Do we even have 4 extra lines lying around? Instead of a direct link, do you want to use one of the serial buses? That will cost you another converter chip, as well as slowing down anything else on that bus (not much, but worth mentioning).

Then there are development costs. These are non-recurring, but need to be accounted for. You need to find acceptable parts and set up an account with suppliers who can deliver the quantities necessary in time alloted. You need to find a spot on the board for your A2D converter and any other necessary electronics. You might have to re-route other systems to accommodate the additions. You will have to add support for the hardware into the OS and then document it for devs to play with.



Now, what is the actual benefit of an ambient light sensor? What can you do with the sensor that you can't do without it? Basically the sensor allows you to be lazy and not manually adjust the screen brightness, possibly saving you a couple percent on battery run time.



I know it may be asking a lot, but please consider these things when making your requests. Just because something might be "cool", try to think about everything involved with adding it to an already jam-packed device with such a limited design budget an an already set (and very low) retail price. Just because you can think of one potential use for a feature doesn't mean that feature is necessary or even desired. Think - how many actual users will appreciate that feature? How often will they use it? Is it possible they could get the same result using already existing features?

I'm not trying to be condescending, but your dozen or so requests in the last few weeks seem to share a common theme: They are all of limited use, and none of them consider the actual difficulty of being fulfilled.

 

[timofonic]

Don't count with people changing the screen brightness all time, even if done will not be in an optimal way as using an ambient light sensor. A gaming console is for enjoy, not for being a pain in the ass.

Didn't the used TMS320F281x features a built-in ADC? I think all this OMAP thing is designed for PDAs and cellphones, so it's ready for things like this.

Didn't you read my entire post? I already posted there are ambient light sensors with built-in ADC.

About extra cable, maybe it's possible to use the monitor connector. I'm not sure about the LVDS standard, but probably there are some serial/i2c line designed for this kind of things as usual in the embedded market.

http://www.avagotech.com/products/product-...navId=apds-9007

- APDS-9007 from Avago Technologies at "Pricing $0.45 at moderate volume"
- TAOS offers some interesting light sensors with digital output (SMBus or I²C).
- Intersil ISL29001.
-ROHM's BH1710FVC
- Hamamatsu Corporation offers a wide bunch of photo sensors, some of them with digital outputs.


Who knows, maybe even the backlight controller used in the TFT screen already supports a light sensor by some analog input. Where it is in the system? Because those controllers quite usually support analog light sensors too.

 

[javaJake]

See my sig.

 

[timofonic]

See my sig.

It's not your text and please keep on topic. I would prefer to be "blamed" by the responsible ones

And please remember I'm discussing this. I think it's enough interesting for the system and can be even cheaper to do if the backlight controller supports a light sensor (very probably). Anyone can say the used TFT model and/or the backlight controller?

 

[javaJake]

What do you mean it's not my text? Of course it isn't. MWeston said those words, and they apply to quite a few of your topics. See the original post for even more detail.

Basically, it isn't worth it. Any more features, and they will have to raise the price. When the price goes up, sales go down, because the price is already maxed out in terms of what people will pay.

 

[squeakypants]

I agree on both sides: an ambient light sensor could be very useful, but the design is basically finalized and it probably can't be included without making a revision to the PCB.

However, you have to remember, while it's $0.20 to add one, you also have to think about getting a dealer and shipping it. It could end up being twice that.

However, I don't think it's a matter of money as much as just hassle. They'd have to go though a lot to put it in, when the only thing it actually does is adjust brightness automatically instead of having the user do it manually. Plus, I think I read MWeston say already that it wouldn't be visible in sunlight, regardless of the backlight, so the usefulness isn't THAT high.

It'd be nice, but it's not a big deal. You guys don't have to get on timophonic's back though; he's just giving his input. Of course, he could have just made one thread instead of many

 

[mafia-man]

Personally, I con't care about ambient sensors, but just one warning: Don't make the same mistake the geniuses at Nokia made when they put a sensor in the N810. They found just about the only spot where the sensor would allways be covered by the user's thumb, thus rendering its usefulness to merely a tad over zero.

If the developers decide to put one in, they better think long and hard about where to stick it. Oh, and make sure it can be turned off by the user.

The N95 one is perfectly placed by the front camera above the screen.... didn't notice it for about two months just thought it was my eyes going funny in the light lol

 

[Squidge]

And please remember I'm discussing this. I think it's enough interesting for the system and can be even cheaper to do if the backlight controller supports a light sensor (very probably). Anyone can say the used TFT

A lot of your suggestions are valid and nice to have; however, this is all fine until they come back with "The Pandora is almost all built and ready for shipping, but we are still waiting for the ambient light sensors - they currently have a lead time of 12 weeks and we can't buy from anywhere else without redesigning the PCB." or even worse "The ambient light sensor we designed for is no longer mass produced, so we can only order 1000. We are going to have to redesign the PCB."

Basically, the more components you add, the greater the chance of the entire product being delayed due a part going out of production or having large lead times by the time you go "Right, everythings perfect, order 3000 for first major production run".

I'm sure every one wants the Pandora as fast as possible, which means as few a parts as possible, from as few a suppliers as possible.

 

[Nova]

It's not used on MY laptop, therefore, I don't need it.