Keyboard LED

P

Paul Vinten

Guest
Ok, I'm looking to change the LED's in my keyboard (it's getting a full
makeover) and I've just ordered (not paid for yet mind) some JA27E from
www.maplin.co.uk My multimeter was knackered, so I just ordered the first
3mm blue LED's that I came accross. When I ordered them, I bought some more
fuses for my multimeter, so that I could accurately measure what ampage and
voltage my led's run at. I've discovered that they run on 15mA and 2V, but
the LED's I've ordered are rate max 3.3V and 50mA...

Are my new LED's going to be very dim? will it not make any difference, if
anything INCREASE the life? Will I be better off getting the JA22Y which has
lower max mA -age?

It has been a while since I've done any electronics, so all advice
gratefully received...
 
"Paul Vinten" <paulvinten@blueyonder.co.uk> schreef in bericht
news:gBEJc.19848$q8.4365@fe1.news.blueyonder.co.uk...
Ok, I'm looking to change the LED's in my keyboard (it's getting a full
makeover) and I've just ordered (not paid for yet mind) some JA27E from
www.maplin.co.uk My multimeter was knackered, so I just ordered the first
3mm blue LED's that I came accross. When I ordered them, I bought some
more
fuses for my multimeter, so that I could accurately measure what ampage
and
voltage my led's run at. I've discovered that they run on 15mA and 2V, but
the LED's I've ordered are rate max 3.3V and 50mA...

Are my new LED's going to be very dim? will it not make any difference, if
anything INCREASE the life? Will I be better off getting the JA22Y which
has
lower max mA -age?

It has been a while since I've done any electronics, so all advice
gratefully received...
Click to expand...
Paul,

The question is: What output drives your LEDs?

A single transistor? (Not very likely these days.)
Then I guess you'll have a series resistor of 180-220Ohm. You can lower it
to 100-120Ohm to obtain the same 15mA you had. You can go as low as 33Ohm to
get 50mA. Most transistors have no problems with 50mA, otherwise you can
replace them. I don't know that blue LEDs but I think there's no need to go
to 50mA. Even 15mA may be enough. The higher the current the lower the life
expectancy of the LED.

The output of a (dedicated) chip with a series resistor?
Then you can lower the series resistor as mentioned above to become 15mA.
Beyond 15 mA you will almost certainly blow the output of the chip.

The output of a chip without series resistor?
You can always try but don't expect to have much light from the blue LED.
You'll have to add some electronics (p.e. open collector/drain buffers,
transistors or FETs) to drive the LEDs.

petrus bitbyter


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.720 / Virus Database: 476 - Release Date: 15-7-2004
 
It's a chip with a resistor between the chip and the power supply... (as far
as I can tell) so, I'd rather not touch it if I don't have to.

which ones would be brighter? the JA27E or the JA22Y?

"petrus bitbyter" <p.kralt@reducespamforchello.nl> wrote in message
news:GpGJc.146112$3N6.111399@amsnews05.chello.com...
"Paul Vinten" <paulvinten@blueyonder.co.uk> schreef in bericht
news:gBEJc.19848$q8.4365@fe1.news.blueyonder.co.uk...
Ok, I'm looking to change the LED's in my keyboard (it's getting a full
makeover) and I've just ordered (not paid for yet mind) some JA27E from
www.maplin.co.uk My multimeter was knackered, so I just ordered the
first
3mm blue LED's that I came accross. When I ordered them, I bought some
more
fuses for my multimeter, so that I could accurately measure what ampage
and
voltage my led's run at. I've discovered that they run on 15mA and 2V,
but
the LED's I've ordered are rate max 3.3V and 50mA...

Are my new LED's going to be very dim? will it not make any difference,
if
anything INCREASE the life? Will I be better off getting the JA22Y which
has
lower max mA -age?

It has been a while since I've done any electronics, so all advice
gratefully received...



Paul,

The question is: What output drives your LEDs?

A single transistor? (Not very likely these days.)
Then I guess you'll have a series resistor of 180-220Ohm. You can lower it
to 100-120Ohm to obtain the same 15mA you had. You can go as low as 33Ohm
to
get 50mA. Most transistors have no problems with 50mA, otherwise you can
replace them. I don't know that blue LEDs but I think there's no need to
go
to 50mA. Even 15mA may be enough. The higher the current the lower the
life
expectancy of the LED.

The output of a (dedicated) chip with a series resistor?
Then you can lower the series resistor as mentioned above to become 15mA.
Beyond 15 mA you will almost certainly blow the output of the chip.

The output of a chip without series resistor?
You can always try but don't expect to have much light from the blue LED.
You'll have to add some electronics (p.e. open collector/drain buffers,
transistors or FETs) to drive the LEDs.

petrus bitbyter


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.720 / Virus Database: 476 - Release Date: 15-7-2004
Click to expand...
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top