Infrared LED brightness
Question for N900 hardware experts: is there any way to control the brightness of the infrared LED? I'm working on a program that uses infrared (Pierogi), and it appears that the brightness of the LED can vary somewhat between N900s. I don't see any brightness controls in the lirc_rx51 device driver, but maybe there is some other mechanism to adjust it? Thanks!
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Re: Infrared LED brightness
iirc the ir port was tied in some way to the kernel, maybe the use of a different kernel like kp could affect it's output.
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Re: Infrared LED brightness
@Copernicus: May I suggest you ask Pali!
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Re: Infrared LED brightness
Just a wild guess (I don't have my N900 here atm):
Have a look at: Code:
/sys/class/leds/If so you should find a file called brightness which accepts values of 0-255. Assuming the LED supports different brightness levels (most of them only switch on and off) you can check the result with any digital camera (photo, video, webcam) pointing at the N900's IR emitter since their sensors partially cover the IR spectrum. |
Re: Infrared LED brightness
@sulu,
Unfortunately I only see the R/G/B, the keyboard leds and the vibrator.. so no IR there :( |
Re: Infrared LED brightness
Hey, poking around in the rest of the /sys directory turned up a /sys/devices/platform/lirc_rx51 directory. I have no clue what the contents signify, but it even has a subdirectory called "power" (although it contains just one file called "wakeup", and that looks empty).
I guess I should ask, might there be any documentation around for any of this? :) |
Re: Infrared LED brightness
CIR output is PWM type so there is no brightness control, just only on ( maximum ) and off
but between "always on" and off state can be a lot of average brightness values. from datasheet : • Transmit mode only (receive mode is not supported) • Free data format (supports any remote-control private standards) • Selectable bit rate • Configurable carrier frequency • 1/2, 5/12, 1/3, or 1/4 carrier duty cycle |
Re: Infrared LED brightness
please come up with something soon guys.people like me,who don't wanna mess around with their lovely N900s so much,would all be very grateful.Pierogi is a great programme,but the fault lies in my mobile phone.The Infra red LED brightness is very low.There HAS to be a way to adjust this somehow.its an open challenge to all you good people who're good at crackin' stuff.cheers people.
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Re: Infrared LED brightness
just an idea
why we dont connect an infrared usb chip to the n900 via hen and make pierogi transmit via it ? |
Re: Infrared LED brightness
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I'm not a hardware guy, so I don't really do this sort of thing, but I think it'd be easy to rework the Pierogi back-end to tie it to other IR devices... |
Re: Infrared LED brightness
http://i44.tinypic.com/k1tc02.png
According to schematics, the current through the LEDs is controlled by the the 220R resistors. Replace them all with 110R resistors for maximum IR lols. ...Although, the fact they have used two transistors in parallel implies that the forward current is already quite high for them (the transistors). So, will doubling it cause any problems? If not, why use 2 transistors?? Can the LED even take any MOAR juice anyway? Who will try to find out? |
Re: Infrared LED brightness
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Two transistors in parallel like that have to have the same resistance (with not much tolerance). If there not one transistor will end up taking all of the load. This will destroy both transistors quickly. Two transistors allow double the current of one. Most 5mm 860nm infra-red LED's I have seen have a max forward voltage of 1.8V. 940nm LED's can have even lower voltage (1.2-1.6) Increasing voltage above this will reduce light output due to increased temperature and eventually fry the LED. I am certainly not going to try. |
Re: Infrared LED brightness
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It fairly easy to make a receiver and cheap http://www.networkedmediatank.com/sh....php?tid=29013 that is a receiver using a1/8 phono jack, Im sure you could use a mini usb wire instead. For a sender there are plenty that are pre made for iphones using the headphone jack or that could easily be made as well |
Re: Infrared LED brightness
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case ONLY one transistor is on the current flow thru this transistor ( one , singleton ) will be the same as both transistors are on state. only the led current will double wen both transistors are on. Ic( max) = ( Vbat - Vled - Vcesat ) / ( R / 2 ) -----> ~ 15 mA all values can be considered constants ! i am sure, transistor can sink more than that the maximum brightness without mods is achieved on 1/2 duty cycle. ( register settings ) average led current will be ( 50% duty , both on ) : 1/2 * 15 mA * 2 = 15 mA and this value can be supported by any led continuous mode ! AFIK peak led current on traditional ir remote is 1A !!! much higher than n900 ir led current across all n900 the ir power is low compared with an genuine ir remote control |
Re: Infrared LED brightness
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Re: Infrared LED brightness
@ sixwheeledbeast
you have the right to believe what you want but who wants to be always right lose the chance to know the truth yahoo answers in not a reference, at least for me, over my personal achievement when i designed animated led panels for public advertising . ( from processor assembly code to schematics and mechanical design ) finally, who is right ? you or nokia engineers ? over and out |
Re: Infrared LED brightness
@blue_led
It wasn't the only reference I found, but the best explained one. This is what I was taught, not what I believe. It sounds like you have a lot more experience in this, so naturally I will take what you say as the truth. Finally, why does this have anything to do with comparing myself and Nokia or there engineers? |
Re: Infrared LED brightness
so now we must ask H-E-N developers to attach an external ir device ?
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Re: Infrared LED brightness
still nothing for me?very sad.:(:(:(
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Re: Infrared LED brightness
Just a few things:
The brightness of the IR transmitter in the N900 is what it is. The best you can do is select the 1/2 duty cycle. You can't make it brighter with software, nor would you want to if you could. As for the bits about transistors: The case sixwheeledbeast is making is valid for some applications, but not this one. Part of the reason being, the system is controlling the duty cycle on the led, so the chances of either heating up enough to cause this effect is minimal. As for why it's using two, it is probably to control current. When one is on, there are only 2 resistors (equaling 110 miliohm), when both are on, there are 4 (equaling 55 miliohm). And yes, the calculations involved are simple enough to determine that most leds would have no problem handling that. |
Re: Infrared LED brightness
1)
the only situation when sixwheeledbeast's statement is true,is bipolar transistors PIN to PIN direct connection due to transistors electrical characteristics misfit is not the case here because base pin have a large resistor ( 4.7 k ) and colector resistors 110 ohm and this make the equilibrium between transistors 2) @ woody14619 resistor notation is 220R ----> 220 Ohm, 2R2---> 2,2 Ohm, etc 220 R is noT 220 miliohm 55 miliohm is very close to short circuit or high power FET transistor on resistance, with this value is like direct apply battery voltage on led. for sure is not real case. without specs i say the ir led on n900 can handle 100 mA pulsed current and the resistors can be replaced with a lower value. the problem is low voltage in transistor's "base" combined with low hFE ( 80 typical for digital transistors ) ----> low base current -> low colector current ( resulting 2 transistor needed ) . a transistor with hfe = 80 & 1,8 V Vout of CIR output ( not sure ) can handle ~ 20 mA in cold weather far lower for high peak current needed for "mall tv fun shutdowner" |
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