>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 16 September 2005 04:48
>To: piclist@mit.edu
>Subject: [EE] LED Speed Test
>
>
>I did a quick round of tests to see how fast LEDs are. It's 
>not super- precise because although I used a photodiode and 
>reverse-biased 
>it, I didn't use an amp. But for the speed I cared about it was fine.
>
>I tested IR, Red, Green, Blue, and two different white LEDs - an old 
>yellowish one and a new bluish one.
>
>The thing that surprised me was how fast the red, green and blue 
>LEDs were. In the past I have only measured IR LEDs and that was 
>when I made a mental rule-of-thumb that 500 KHz was the upper 
>limit for LEDs. Well, Red LEDs are a lot faster, and green and blue 
>are right there too.
>
>Also surprisingly, white LEDs are somewhere in between. Just fine 
>for propeller clocks and stroboscopes :)
>
>Take a look:
>http://bobblick.com/led_speed_test/
>
>Bottom trace is input (LED current), top trace is output (photodiode 
>current).


Bob, did you measure the rise/fall time of your signal source?  Lead inductance and stray capacitance can also have a big effect, so an experimental setup using the full length LED wires etc. may be showing poorer results than is actualy possible.  Obviously this has proven they are more than fast enough for a propeller clock though!

Regards

Mike

=======================================================================
This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
law. If you are not the intended recipient of this message, you must
not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
received this e-mail, and return the original to us. Any use,
forwarding, printing or copying of this message is strictly prohibited.
No part of this message can be considered a request for goods or
services.
=======================================================================

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist