geekhack
geekhack Community => Keyboards => Topic started by: fateswarm on Wed, 29 May 2013, 07:18:58
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also see http://geekhack.org/index.php?topic=44060.msg911766#msg911766
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I'm currently investigating something and I wonder what is the common current required by a regular mechanical keyboard or one with backlit keys. I know 5V is used by all such devices so Current must dictate the actual power required, well at least if it's constant.
I notice some USB devices report to the OS (on the Device Manager hub's properties) that they need 500mA while they look 'small'. A keyboard reported 100 which seems unrealistic. The 'lowly' smart card reader here reports 500 :eek:.
Since I don't have an actual physical meter and only those manufacturer reports, I wonder if anyone has measured it or knows it more or less.
PS. Could a massive discrepancy between a backlit mechanical keyboard reporting 100 and actually drawing 500 or more make the USB subsystem misbehave somehow (even if in some cases the current could be sustained if the one required was reported accurately by the device)? Because I'm investigating something like that.
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I'm currently investigating something and I wonder what is the common current required by a regular mechanical keyboard or one with backlit keys. I know 5V is used by all such devices so Current must dictate the actual power required, well at least if it's constant.
I notice some USB devices report to the OS (on the Device Manager hub's properties) that they need 500mA while they look 'small'. A keyboard reported 100 which seems unrealistic. The 'lowly' smart card reader here reports 500 :o .
Since I don't have an actual physical meter and only those manufacturer reports, I wonder if anyone has measured it or knows it more or less.
PS. Could a massive discrepancy between a backlit mechanical keyboard reporting 100 and actually drawing 500 or more make the USB subsystem misbehave somehow (even if in some cases the current could be sustained if the one required was reported accurately by the device)? Because I'm investigating something like that.
here is what mine looks like
[attach=1]
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CM Storm Trigger... Thing eats up energy like no one else.
(http://img845.imageshack.us/img845/802/energyv.jpg)
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Just because they say 100mA, 400mA, 500mA or whatever, it doesn't mean they actually use it all ;)
Typical Cherry or Alps based board these days will be a few 10s of mA. A Model F or M is a bit over 100mA. Backlighting methods vary, so it's hard to give a figure for it - anything between 100mA and 500mA is feasible.
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Aye. Device Manager reported currents are reported and not independently measured. If I'm not mistaken, a device could report something new on the fly though.
They are still useful though, they may affect system behavior, e.g. I supposed they may be 'punished' by the subsystem if they report little and drain everything, well, if the USB subsystem can detect that.
Typical Cherry or Alps based board these days will be a few 10s of mA. A Model F or M is a bit over 100mA. Backlighting methods vary, so it's hard to give a figure for it - anything between 100mA and 500mA is feasible.
That's my main center of investigation now. This backlit keyboard reports 100 which sounds too optimistic.
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I dunno, using high-brightness LEDs at low current could be less than 100mA, but maybe not by much. About 1mA per LED seems perfectly possible these days without costing too much.
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I looked a bit into the spec (https://en.wikipedia.org/wiki/Universal_Serial_Bus#Power) and market reality a mess. 100mA is supposed to be always required initially (which might explain a lot of '100mA' on device managers) but then after that initial negation a device is free to ask up to 500mA. Now whether that is truly what is drawn or if the OS accurately reports that or waits for the device for confirmation of a new current I do not know.
What is certain is that there's tons of dodgy implementation in the market; devices drawing tons of power above that specified and the icing: "Devices" that aren't even negotiating anything electronically; just drawing current, like lamps and fans and vacuum cleaners (yes).
What's interesting is that it appears there's is little control - at least proactively - by the host bus: Devices can usually pump whatever they want without negotiating it.
It appears what made it worse was the requirement of the bus to act as a charger supply so lots of devices (manufacturers) would whine that there's too much work needed before they are able to pump the juice. So there appears to be little future for restricting it, more likely is the opposite, to give even more freedom to chargers.
tl;dr: have a powered hub ready if you suspect power issues, USB spec itself won't easily protect you.
I dunno, using high-brightness LEDs at low current could be less than 100mA, but maybe not by much. About 1mA per LED seems perfectly possible these days without costing too much.
Thanks for the info.
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I looked a bit into the spec (https://en.wikipedia.org/wiki/Universal_Serial_Bus#Power) and market reality a mess. 100mA is supposed to be always required initially (which might explain a lot of '100mA' on device managers) but then after that initial negation a device is free to ask up to 500mA. Now whether that is truly what is drawn or if the OS accurately reports that or waits for the device for confirmation of a new current I do not know.
What is certain is that there's tons of dodgy implementation in the market; devices drawing tons of power above that specified and the icing: "Devices" that aren't even negotiating anything electronically; just drawing current, like lamps and fans and vacuum cleaners (yes).
What's interesting is that it appears there's is little control - at least proactively - by the host bus: Devices can usually pump whatever they want without negotiating it.
It appears what made it worse was the requirement of the bus to act as a charger supply so lots of devices (manufacturers) would whine that there's too much work needed before they are able to pump the juice. So there appears to be little future for restricting it, more likely is the opposite, to give even more freedom to chargers.
tl;dr: have a powered hub ready if you suspect power issues, USB spec itself won't easily protect you.
I dunno, using high-brightness LEDs at low current could be less than 100mA, but maybe not by much. About 1mA per LED seems perfectly possible these days without costing too much.
Thanks for the info.
Let's just add it up
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Let's just add it up
ahha, but those are just typical values. Otherwise we'd have keyboard pulling (20mA x 104) 2 Amps of current for backlight. That's one thing I wish more people understood, just because they are rated at 20mA doesn't mean you need to be pumping 20mA through each LED, in my experience, most LED's are plenty bright at 5mA OuO
Also, as soarer said, depending on how the LED's are controlled, you may never have more than a few of them turned on at any instant of time.
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Let's just add it up
ahha, but those are just typical values. Otherwise we'd have keyboard pulling (20mA x 104) 2 Amps of current for backlight. That's one thing I wish more people understood, just because they are rated at 20mA doesn't mean you need to be pumping 20mA through each LED, in my experience, most LED's are plenty bright at 5mA OuO
Also, as soarer said, depending on how the LED's are controlled, you may never have more than a few of them turned on at any instant of time.
O-rly?
Explain why Cooler master recommends a 2 AMP ac adapter for their Trigger Keyboard... HM...... ridddle me that... kmiller 8.. riddle me that.... ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh >:D >:D >:D >:D >:D
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LOL at your math. milliamps, or thousandths of an amp. 20mA x 104 = .208 Amps.
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Are you saying that a fully lit keyboard can draw more than 2.something Amperes? That's not USB compliant unless it's a charger. I wonder if some USB hosts will punish such a device actively.
What's scarier is that 2+ A may be more than the entire hub. This powered hub here is 2.5A.
LOL at your math. milliamps, or thousandths of an amp. 20mA x 104 = .208 Amps.
Nope, that'd be true with X10.4
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.002 x 104
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.002 x 104
http://www.wolframalpha.com/input/?i=20ma+times+104
Your mistake is that they are 20 of those not 2.
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.002 x 104
http://www.wolframalpha.com/input/?i=20ma+times+104
Your mistake is that they are 20 of those not 2.
True. Thanks for pointing that out. Carry on without me...
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Explain why Cooler master recommends a 2 AMP ac adapter for their Trigger Keyboard... HM...... ridddle me that... kmiller 8.. riddle me that.... ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh >:D >:D >:D >:D >:D
An even more urgent question is: why they didn't do the same for the TK. It's a christmas tree on full power. :)
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True. Thanks for pointing that out. Carry on without me...
No problem. I recently turned 20 liters into 200 liters in my engineering class. It made the pipes a few times larger. :cool: :)) :'(
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O-rly?
Explain why Cooler master recommends a 2 AMP ac adapter for their Trigger Keyboard... HM...... ridddle me that... kmiller 8.. riddle me that.... ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh >:D >:D >:D >:D >:D
NOTE: These are all the assumptions of me, don't take none of this **** as fact.
well, going off the math I used. I would assume they recommend a 2 amp AC adapter so that they can run all 109 LEDs at a constant 20mA instead of using some controller magic to control them, which would also explain why the Trigger does not have "levels" so you could adjust brightness, just on/off because it's pulling all power for the LEDs from the wall wart, not the USB connection. Unless it does work backlight with just USB (which I don't know OnO).
Also, I based my previous response assuming we were staying within the 500mA "limit" of USB OuO
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Explain why Cooler master recommends a 2 AMP ac adapter for their Trigger Keyboard... HM...... ridddle me that... kmiller 8.. riddle me that.... ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh >:D >:D >:D >:D >:D
An even more urgent question is: why they didn't do the same for the TK. It's a christmas tree on full power. :)
I don't think it matters as long as your psu can handle it, there's probably a very large overhead built into "modern" usb because the manufacturers know that some people get crazy with it...
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The Trigger does have backlighting via USB. It also does have brightness level adjustment.
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I based my previous response assuming we were staying within the 500mA "limit" of USB OuO
It is 500. The spec allows more but only for chargers. I know it's a bit weird because if chargers, why not others? Probably because they are pressured to allow the spec to support phones and whatnot. I doubt though that PC buses have the power to properly charge most of those devices.
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NOTE: These are all the assumptions of me, don't take none of this **** as fact.
The Trigger does have backlighting via USB. It also does have brightness level adjustment.
OuO
I'll see myself out
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I don't think it matters as long as your psu can handle it, there's probably a very large overhead built into "modern" usb because the manufacturers know that some people get crazy with it...
Are you saying it's solely depended on PSU? I thought it was also USB bus limited.
If it's true it might explain my laptop crapping out devices like external HDDs or whatnot without a powered hub. :rolleyes:
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I don't think it matters as long as your psu can handle it, there's probably a very large overhead built into "modern" usb because the manufacturers know that some people get crazy with it...
Are you saying it's solely depended on PSU? I thought it was also USB bus limited.
If it's true it might explain my laptop crapping out devices like external HDDs or whatnot without a powered hub. :rolleyes:
yea.. some older psus have very low amp 5vsb, or low 5v in general and I remember them crapping out on me
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It's perfectly true:
"How many Brightness settings does Triggers LED Backlight have?
By default Trigger has 3 levels, but if you want it to be even brighter or want to use power hungry USB devices on Triggers built in USB hub, you can connect a standard 5VDC PSU.
As soon as the PSU has been connected, you will be able to boost the LED brightness setting by 2 additional Levels!
If you have any questions please dont hesitate to submit a support ticket and contact us."
That's like implying they bring the spec to its knees just before doing those extra levels. ^-^
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Oh dear, this thread has been tp4'd :(
20mA on the spec sheet is just a reference value for the other parameters, like Vf and mcd etc.
For example a single rated Vf will be given that is only correct when pasing 20mA through the LED. There will also be a graph showing how Vf changes with different currents later in the datasheet (if it's a good one).
Put a bigger resistor in, or some other current control, and there's no problem running it at FAR less current. PWM could also be used to share current around over time.
Use decent LEDs, and that will still be plenty bright enough for backlighting. But of course some makers will still try and use the cheapest, or burn your eyes out :(
As for USB hubs etc, in practise I've found that some will trip out if you go over 500mA. That's why external drives usually come with that double-headed cable!
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The CM Storm Trigger has 3 backlight levels as said before and there's 2 others you may "unlock" if you use an external 5v power source (which I have).
But anyways, the backlight is already strong at level 3, which is why I use it at the lowest setting and there's no reason to use level 4 or 5, unless you're visually impaired or want to show off your keyboard.
Now, the main use for the external power source is to power up whatever I may insert into the USB HUB that's right near the mini-USB connector, on which I can put an external HDD, a headset or something like that.
Without the external power source, it's just impossible to use anything besides a memory stick on the keyboard without getting a "USB Power limit exceeded" warning on my computer.
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Yeah, that makes sense since even at low brightness there might not be much power left for other devices on the hub.
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Without the external power source, it's just impossible to use anything besides a memory stick on the keyboard without getting a "USB Power limit exceeded" warning on my computer.
You're lucky it does that. Here Intel 6 craps out devices by shutting them off at the power level. :)
[Or they just die on their own by luck of Power. Or it might be a PSU thing.]