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Author Topic: PC IR remote LED addition  (Read 5072 times)

snow veil

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PC IR remote LED addition
« on: March 12, 2004, 12:39:31 AM »

As per Ronin's request in the PC Remote thread, I figured it'd be neat to add an LED to the circuit.  After about a minute of searching I found someone who has completed the effect ( http://www.electronics-lab.com/projects/pc/019/ ), but I was wondering if there was a simpler solution than using dual transistors and a cr2032 battery.  So with a little help from skylined, I came up with this:

original:


My idea:



Now, Sky mentioned how tired he was upon reviewing my idea, so I was hoping that possibly a few electronic-literate folks might be able to help me out.  I understand the very basics of a transistor, but I don't know enough about them to really get a grasp of what is needed exactly.  From examples I've seen, the resistor (that I've labeled R3) going into the base of the transistor is usually a large value, around 10k or more.  Do transistors simply need such low current to operate that any more would be overkill/ damage the transistor?  Help me please :).  Also, if you wouldn't mind lending a "sure, that will work", or "nope, that's not gonna do it...here's why, and (maybe) here's what you COULD possibly do..."  I'd greatly appreciate it :)

I'm willing to learn this stuff, but I'd like some input to sort of lead me along to make sure I'm not blindly thinking I'm in the right or wrong.  

Thanks
-mike

viridius

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PC IR remote LED addition
« Reply #1 on: March 12, 2004, 01:04:17 AM »

R3 can be a high value because the base of a transistor is pretty sensitive.  But don't put it in series with your IC.  Have it be an offshoot of the same line, but go straight to the transistor's base.  The LED, likewise, should be an offshoot and not inline.  Connect the cathode to the collector of the 2N2222.
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snow veil

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PC IR remote LED addition
« Reply #2 on: March 12, 2004, 09:04:24 AM »

Thanks for the help viridius.  You know, I thought about the high valued resistor being in series with the + leg of the IR module last night when I was about to sleep...wondering if it would pose a problem...hehe.  I didn't pick up on running the LED on another line, though.  Shouldn't the LED anode be facing the transistor, though, since I'm switching ground through the transistor?  I could be reading it incorrectly, I don't know.

Anyway, here's a revised schematic:

viridius

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PC IR remote LED addition
« Reply #3 on: March 12, 2004, 06:31:05 PM »

That should work.
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linear

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PC IR remote LED addition
« Reply #4 on: March 12, 2004, 10:33:43 PM »

Quote from: snow veil
Shouldn't the LED anode be facing the transistor, though, since I'm switching ground through the transistor?  I could be reading it incorrectly, I don't know.

Anyway, here's a revised schematic:



The LED is correct as shown in your diagram--the current flows from the +5V supply, through the LED and into the collector, then out the emitter to ground.

One handy way to visualize the current flow is that the arrow on the emitter of the transistor symbol shows you the direction of the current flow. Since your arrows on the LED and emitter both point towards ground in your diagram, it should work.
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snow veil

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PC IR remote LED addition
« Reply #5 on: March 13, 2004, 01:30:42 AM »

thanks for the help guys.  Goldmine electric was out of 2n2222's so I went ahead and ordered some 2N3903's instead.  As far as I can tell the only difference between them is the max current sent from the collector to emitter, which is still at 200mA, far more than I'll be supplying the LED with.

I guess it's just time to wait for the goodies to arrive and It'll be play time again :)

Ronin

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PC IR remote LED addition
« Reply #6 on: March 15, 2004, 05:01:08 AM »

Wooo Ha!, Well lets see If it works. ;)
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snow veil

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PC IR remote LED addition
« Reply #7 on: March 25, 2004, 05:39:50 PM »

well, I just got the parts in the mail today and they're not working quite as planned.  With the previous circuit, the LED stays on all of the time but flashes slightly when the remote is pressed.  With this new circuit: (transistor switching 5v instead of ground)


The led is barely (and I mean barely) lit all of the time, and flashes in the same fashion.

Does anyone have any ideas on how to solve this dilemma?  It seems as though the transistor isn't letting enough current flow through it to power up or power down the LED when it needs to, but that's just my guess.  The TN3903 datasheet is located here:  (in PDF form)

http://www.onsemi.com/pub/Collateral/2N3903-D.PDF&e=7413

Would it be possible (or wise) to take out the 47k resistor?  My guess is that the transistor for some reason or another isn't switching on or off when it needs to.

Another idea that BalefireX had was to change the circuit accordingly:



The problem is, I don't have a walrus handy and don't feel like getting a license and such to keep one.  I could always move to the zoo....but this is a last resort.

ClearCaseMan

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PC IR remote LED addition
« Reply #8 on: March 25, 2004, 05:45:09 PM »

Quote from: linear
Quote from: snow veil
Shouldn't the LED anode be facing the transistor, though, since I'm switching ground through the transistor?  I could be reading it incorrectly, I don't know.

Anyway, here's a revised schematic:



The LED is correct as shown in your diagram--the current flows from the +5V supply, through the LED and into the collector, then out the emitter to ground.

One handy way to visualize the current flow is that the arrow on the emitter of the transistor symbol shows you the direction of the current flow. Since your arrows on the LED and emitter both point towards ground in your diagram, it should work.


Hey Rob welcome to the GT forums
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snow veil

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PC IR remote LED addition
« Reply #9 on: March 25, 2004, 06:48:37 PM »

ok, removing the 47kohm resistor does nothing, it makes me now wonder if the 47k resistor maybe insn't enough?

DATA on the IR module puts out 3.7v, gets sent through the 47k ohm resistor, then to the transistor base.

I tried putting 2 47kohm resistors in series, lemme get a snippet from irc.  This is what I think, anyway.

[18:34] <snow_veil> with signal: transistor base gets 1.7v
[18:34] <snow_veil> without signal: transistor base gets 1.4v
[18:35] <snow_veil> I want it to be that when the base gets a voltage, it allows current to flow between the collector and emitter
[18:35] <x24> don't the emitter get it's current from the collector?
[18:36] <snow_veil> yeah
[18:36] <x24> like the base makes the connection between the c and e
[18:36] <snow_veil> yup yup
[18:36] <x24> so the current going into the led is coming from the collector
[18:36] <snow_veil> essentially yes
[18:36] <snow_veil> it's like this
[18:37] <snow_veil> 5v from voltage reg -> Collector ->(while Base gets signal)-> Emitter ->100ohm -> led -> gnd
[18:37] <x24> yes
[18:37] <snow_veil> I'm trying to find the cutoff point from where the base will allow/disallow current to flow from the collector to the emitter
[18:38] <x24> hmm
[18:38] <x24> i see what you mean
[18:38] <x24> maybe it's not "connecting" enough
[18:40] <snow_veil> see the transistor is now allowing current to go through at 1.4v, I need to find the point at which it will disallow current to flow within a certain tolerance so that it can be switched on and off with the resistance from my IR module


any ideas?
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