Reading a Anemometer reed switch with a 555 timer

Hi!
I have an Anemometer (3-cup wind sensor) at the side of my house for reading wind speeds. When the wind blows the cups turn which operates a reed switch inside the unit. Each turn gives 2 pulses from the reed switch.
I ran the reed switch contacts through an opto-isolator. The other side of the opto-isolator is linked to an I/O card on my PC for wind monitoring (obviously!).
The reed switch had about 5 years of operation according to the anemometer manufacturers.
Unfortunately I have 'welded' the contacts on the reed switch after only one month! It seems that connecting the reed switch in series with the LED inside the opto-isolator has passed too much current through the reed switch.
What I am after is a component that can trigger a higher load (it's only an LED!) from a extremely low voltage/current input. The reed switch will then be switching a 'next to nothing' voltage and therefore last longer!
The reed switch is firing about 5 times each second, so the lower the voltage going through it the better.
I am thinking of using this circuit:
http://www.kpsec.freeuk.com/555timer.htm#buffer
How do I supply a low input voltage to this circuit?
If anyone has any ideas or recommendations that would be excellent!
Thank you very much,
Matt

Posted by Matt on 22/09/2007, at 01:36 GMT

Re: Anemometer

Try running the reed switch to a 2N7002 N channel mosfet FIRST,then use that mosfet to source or sink the LED on the opto. That should
take care of smokin reed switches.
You could also try a Sprauge/Allegro Micro hall effect SWITCH to switch the opto.many good app notes on their website.

Posted by John (riveraj@curtisinst.com) on 11/12/2007, at 15:25 GMT