Easy question for someone.

  • Thread starter jhleslie@googlemail.com
  • Start date
J

jhleslie@googlemail.com

Guest
Hi,

I have a 5mm red flashing LED, I've had it for probably 15 years, I
connected some others that I bought at the same time to my house
burglar alarm. They are are on the bell box and on a warning panel on
the garden shed. They make the alarm system look very scary, I think
any potential burglar would move onto another house after seeing
these.

Now I have moved to another house and I want to do the same again, the
problem is that I can't remember how to calculate the resistance that
I need to put in series.

A similar looking item that is for sale here has a specification as
follows,
Forward voltage: 2.5V
Forward current max.: 55mA

I think that this has something to do with V = I x R but I didn't pay
proper attention at school.

Can somebody tell me what a suitable resistance would be please?

Thanks in advance,
James
 
jhleslie@googlemail.com wrote:
Now I have moved to another house and I want to do the same again, the
problem is that I can't remember how to calculate the resistance that
I need to put in series.

A similar looking item that is for sale here has a specification as
follows,
Forward voltage: 2.5V
Forward current max.: 55mA
Click to expand...
<http://ourworld.compuserve.com/homepages/Bill_Bowden/led.htm>

I think most villians are on to these LED flashers by now, especially
yours having given your name and geographic location by IP via the very
searchable Google Groups.

Whoops :)

--
Adrian C
 
jhleslie@googlemail.com wrote:

I have a 5mm red flashing LED, I've had it for probably 15 years, I
connected some others that I bought at the same time to my house
burglar alarm. They are are on the bell box and on a warning panel on
the garden shed. They make the alarm system look very scary, I think
any potential burglar would move onto another house after seeing
these.

Now I have moved to another house and I want to do the same again, the
problem is that I can't remember how to calculate the resistance that
I need to put in series.

A similar looking item that is for sale here has a specification as
follows,
Forward voltage: 2.5V
Forward current max.: 55mA

I think that this has something to do with V = I x R but I didn't pay
proper attention at school.

Can somebody tell me what a suitable resistance would be please?
Click to expand...
You'll have to tell us your circuit voltage: +5v? +12V?

R (min) = (V? - 2.5) / .055
R (typ) = (V? - 2.5) / .035

The higher your forward current, the brighter the LED.
 
jhleslie@googlemail.com wrote:

Hi,

I have a 5mm red flashing LED, I've had it for probably 15 years, I
connected some others that I bought at the same time to my house
burglar alarm. They are are on the bell box and on a warning panel on
the garden shed. They make the alarm system look very scary, I think
any potential burglar would move onto another house after seeing
these.

Now I have moved to another house and I want to do the same again, the
problem is that I can't remember how to calculate the resistance that
I need to put in series.

A similar looking item that is for sale here has a specification as
follows,
Forward voltage: 2.5V
Forward current max.: 55mA

I think that this has something to do with V = I x R but I didn't pay
proper attention at school.

Can somebody tell me what a suitable resistance would be please?

Thanks in advance,
James
Assume that you have a 12 volt battery or supply some where.
Click to expand...

R = (12-2.5)/0.055 = 173 ohms, ~ 0.5 watts

P.S.
I wouldn't operate the LED at max current.



http://webpages.charter.net/jamie_5"
 
On 15 Feb, 19:16, UCLAN <nom...@thanks.org> wrote:
jhles...@googlemail.com wrote:
I have a 5mm red flashing LED, I've had it for probably 15 years, I
connected some others that I bought at the same time to my house
burglar alarm. They are are on the bell box and on a warning panel on
the garden shed. They make the alarm system look very scary, I think
any potential burglar would move onto another house after seeing
these.

Now I have moved to another house and I want to do the same again, the
problem is that I can't remember how to calculate the resistance that
I need to put in series.

A similar looking item that is for sale here has a specification as
follows,
Forward voltage:    2.5V
Forward current max.:    55mA

I think that this has something to do with V = I x R but I didn't pay
proper attention at school.

Can somebody tell me what a suitable resistance would be please?

You'll have to tell us your circuit voltage: +5v? +12V?

R (min) = (V? - 2.5) / .055
R (typ) = (V? - 2.5) / .035

The higher your forward current, the brighter the LED.
Click to expand...
Thanks for that prompt reply.
Sorry I omitted that vital bit of information. The voltage is 12v. So
I presume that the sum is...
R (min) = (12 - 2.5) / 0.055 = 172 ohms
R (typ) = (12 - 2.5) / 0.035 = 271 ohms

I realise that I will have to hunt through my box for something of a
standard size but 330 would be appropriate.

Thanks again for your help.
Regards
James

Thanks
 
jhleslie@ googlemail.com wrote:
If you MUST post the *same* question to MULTIPLE groups,
put **all** the groups on the To line the first time you post.
http://en.wikipedia.org/w/index.php?title=Cross-post&oldid=240748598
 
"JeffM" <jeffm_@email.com> wrote in message
news:8e680f28-041a-4dee-8ac8-0a96ba0ddb6b@n33g2000pri.googlegroups.com...
jhleslie@ googlemail.com wrote:
I have a 5mm red flashing LED, I've had it for probably 15 years[...]

If you MUST post the *same* question to MULTIPLE groups,
put **all** the groups on the To line the first time you post.
Click to expand...
But many Usenet denizens don't like that.

To get the most out of Usenet, when making a query:

1/ Assume the position of supplication.
2/ Disguise homework problems.
3/ Post first to basic groups and then later to the intelligentsia.
4/ When confused, add questionable responses to your query and repost.
5/ Above all, be clever! Never appear as if you might know something on
your own.
 
In article
<0db55797-7cf3-47d0-93d5-479d504ec57d@l39g2000yqn.googlegroups.com>,
jhleslie@googlemail.com <jhleslie@googlemail.com> wrote:
Thanks for that prompt reply.
Sorry I omitted that vital bit of information. The voltage is 12v. So
I presume that the sum is...
R (min) = (12 - 2.5) / 0.055 = 172 ohms
R (typ) = (12 - 2.5) / 0.035 = 271 ohms

I realise that I will have to hunt through my box for something of a
standard size but 330 would be appropriate.
Click to expand...
If it's an LED which flashes on its own - ie has the circuitry built in -
they normally operate off a 9-12 volt DC supply with no series resistor
needed. I'd guess that's what you bought before.

--
*He who laughs last, thinks slowest.

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
 
JeffM wrote:

If you MUST post the *same* question to MULTIPLE groups,
put **all** the groups on the To line the first time you post.
http://en.wikipedia.org/w/index.php?title=Cross-post&oldid=240748598
Click to expand...
No, please don't.
 
jhleslie@ googlemail.com
I have a 5mm red flashing LED, I've had it for probably 15 years[...]

JeffM wrote:
If you MUST post the *same* question to MULTIPLE groups,
put **all** the groups on the To line the first time you post.
http://en.wikipedia.org/w/index.php?title=Cross-post&oldid=240748598

UCLAN wrote:
No, please don't.
Click to expand...
OP:
Follow the link and ignore UCLAN's bad advice.
 
JeffM wrote:

If you MUST post the *same* question to MULTIPLE groups,
put **all** the groups on the To line the first time you post.
http://en.wikipedia.org/w/index.php?title=Cross-post&oldid=240748598

UCLAN wrote:

No, please don't.

OP:
Follow the link and ignore UCLAN's bad advice.
Click to expand...
OP: No, please don't.
 
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