Don't forget to allow for temperature and ageing effects. What works today with
a minimum current at 23 deg C will not work years from now at 40 deg C or after
the opto has degraded by 50%. Humidity can also cause problems.





Graham North <graham.north@LANDINST.COM>
29/02/2000 08:17


Please respond to pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>

To:   PICLIST@MITVMA.MIT.EDU
cc:    (bcc: Nick Mitchell/GBPTD/ABB)
Subject:  Re: Optoisolated RS485 input [OT]

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Remember to experiment with Led current and use the lowest
possible value that reliably turns on the opto.

I have read (and I suppose it is common sense when you think
about it) that opto life is directly proportional to Led current.

I know Leds can take much "abuse" but it will shorten their life.


Graham