Subject:
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Re: Homemade LED Bricks
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 12 Nov 1999 03:23:05 GMT
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Original-From:
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"Keith Miller" <kmiller@talon.net>
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Viewed:
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1005 times
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basicly.. it's i*r=v where i = current in amps and r = resistance in ohms
and v = voltage in volts..
so..
If we want to find out the resistor's value.. we re arrange it like so..
r = v/i
so 10 millamps (typical led current) = .01 Amps..
And at 9 volts it becomes
r = .01/9
r = 900 ohms
there..
<G>
I went to votech for electronics.. <G>
----- Original Message -----
From: C S Soh <cssoh@singnet.com.sg>
To: <lego-robotics@crynwr.com>
Sent: Thursday, November 11, 1999 10:04 PM
Subject: Re: Homemade LED Bricks
> Michael Gasperi wrote:
>
> > David Johnston <lego-robotics@crynwr.com> wrote in message
> > news:LOBBJCENKNHFLCKICLNNIEODCAAA.djohnston@tinet.ie...
> > > not being an electronic engineer, what is "appropriate"?
> >
> > I'd say 330 Ohm 1/4 Watt.
>
> Er, 330 ohm may be ok for the usual transistor type circuit where the
> nominal supply voltage is 5 volt, if my memory has not failed me.
>
> It may be a bit low, I think, for the RCX where the nominal voltage is 9
> volts which is almost double of 5 volt. So maybe a resistance of 680
> ohm would be more "appropriate"?
>
> But then I'm not an electronic engineer either. Just wanted to be sure.
> --
> C S Soh
>
> http://web.singnet.com.sg/~cssoh
> ... where air is power
>
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Message has 3 Replies:
 | | Re: Homemade LED Bricks
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| grrr.. I flubbed.. instead of r = .01/9 make it r = 9/.01 ----- Original Message ----- From: Keith Miller <kmiller@talon.net> To: <lego-robotics@crynwr.com> Sent: Thursday, November 11, 1999 10:23 PM Subject: Re: Homemade LED Bricks (...) (25 years ago, 12-Nov-99, to lugnet.robotics)
| | | Re: Homemade LED Bricks
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| (...) Thanks for the enlightenment. I remembered it went something like that. But don't you have to allow for the forward voltage drop across the LED, typically 1.6 volt (still from memory)? That is, the voltage should be 9 - 1.6 = 7.4 volts. So the (...) (25 years ago, 12-Nov-99, to lugnet.robotics)
| | | Re: Homemade LED Bricks
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| Keith Miller writes: > basicly.. it's i*r=v where i = current in amps and r = resistance in ohms > and v = voltage in volts.. > so.. > If we want to find out the resistor's value.. we re arrange it like so.. > r = v/i > so 10 millamps (typical led (...) (25 years ago, 12-Nov-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: Homemade LED Bricks
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| (...) Er, 330 ohm may be ok for the usual transistor type circuit where the nominal supply voltage is 5 volt, if my memory has not failed me. It may be a bit low, I think, for the RCX where the nominal voltage is 9 volts which is almost double of 5 (...) (25 years ago, 12-Nov-99, to lugnet.robotics)
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