I got a new scanner. Super-slim! Maybe only 1.25 inches thick. But it has no power chord. Just the USB connection. Works just fine, but I’m curious… I thought scanners were power-thirsty things.
How is it drawing enough power for the lamp? Or has the technology arrived at a point where the lamp isn’t drawing that much juice?
It is just powered through the USB connection.
The USB specification calls for 5 VDC out @ 500 mA right from the mainboard, which is 2.5 watts - enough to power a couple small motors and a small array of LEDs, as well as some interface electronics. Auxillary USB hubs can provide an even higher current source, using an external wallwart-type power supply.
But how much power do the bulbs use? My old scanner is bright enough to help land a plane or warn boats away from a reef.
Oh and not that I’m complaining. I kida like the way this mamkes my scaner a bit more protable (with its extra skinniness and no need for an outlet).
Would it put an additional burden on my laptop battery that would suck it try faster? Or is that negligible?
David Cronenberg?
Nyuck, nyuck, nyuck.
That was the LED array I referred to. LEDs only draw about 20 mA @ 2-5 V (depending on chemistry/color), and you only need 3 - one red, one green and one blue. They can put out quite a bit of light very efficiently. LEDs have in the last few years begun to supplant the cold-cathode fluorescent bulbs that were previously used, for the most part.
Ah, I see. My scanner doesn’t look like it’s using LEDs but it probably is. It definitely doesn’t have the blinding hot intensity of my old scanner.
And since you asked about how much power it draws from the USB bus, it should be pointed out that there are powered and unpowered hubs, which fork out different amounts of power to each of their ports (powered gives out 500mA per port, whereas unpowered, a.k.a. “bus-powered” hubs only give out 100mA per port). It may very well be that your scanner would not work on a passive (unpowered/bus-powered) hub.
If you plug a power-hungry device into a hub that doesn’t have enough power, windows XP will usually complain at you (with one of those annoying little balloons) and tell you that that’s what’s going on.
I’m on a Mac Powerbook (shiny!) so far, no evil messages of gloom and doom, but thanks for the input.
I also use a PC and it’s an older one, so if I get evil messages, I’ll know why. (Once I get my USB drivers working again :rolleyes: that computer is half-dead right now.)
I’ve got one of those Canon bus-powered scanners and you can tell the lamp is LEDs - looking at it directly it looks white, but if you move your eye so that the light sweeps across your vision, you see a series of red-green-blue stripes - the lamp is very rapidly cycling between the three colours, detecting the reflected image in each of them, then reassembling it into a full-colour image.
Side note; as a result of the colour cycling happening while the scanning head is in full motion, it is often the case that, say, the red sample of a piece of detail on the page will not be taken from the same point as (say) the green sample; superimposing three different coloured sample channels taken in slightly different places can result in fringes of aberrant colour on objects with a sharp edge - it looks just like the chromatic aberration you get with lenses.