variable reluctance sensor/speed switch

[stocky]

I am building a speed switch around a LM2907, but want to add a "pulse" LED
that blinks every time the magnet goes past the senor....I'm having a mental
blank, i'm sure it's easy but can't think how to do it! Should I
capacitively couple the signal from the sensor, so it doesnt mess up the
signal goint to the '2907 and use something like a schmitt trigger to flash
the LED? I know the output amplitude from the sendor varies greatly with
speed, but I need the LED pulses to make it easy to setup. Ant suggestions?

 

[Dan Hollands]

It is not likely you can drive the LED directly from the sensor - you
probably need some type of high impedance device like a mosfet to go between
the sensor and the LED.

--
Dan Hollands
1104 State Road
Webster NY 14580
585-703-2963
QuickScore@USSailing.net
www.QuickScoreRace.com
"stocky" <stocky@capri.net.au> wrote in message
news:uCRSa.7273$OM3.2658@news-server.bigpond.net.au...

I am building a speed switch around a LM2907, but want to add a "pulse"
LED
that blinks every time the magnet goes past the senor....I'm having a
mental
blank, i'm sure it's easy but can't think how to do it! Should I
capacitively couple the signal from the sensor, so it doesnt mess up the
signal goint to the '2907 and use something like a schmitt trigger to
flash
the LED? I know the output amplitude from the sendor varies greatly with
speed, but I need the LED pulses to make it easy to setup. Ant
suggestions?

 

[stocky]

My next thought was do I put the output of the sensor into an opamp and
drive it to a fixed level square wave, then feed that to the LM2907 and the
schmitt trigger (maybe via a cap). That would get me around the varying
input levels. yes?


"Larry" <lnlhilgner@enter.net> wrote in message
news:ca0c527c.0307211846.11049c74@posting.google.com...

"Dan Hollands" <dhollan3@rochester.rr.com> wrote in message
news:<o5TSa.164294$8B.32640@twister.nyroc.rr.com>...
It is not likely you can drive the LED directly from the sensor - you
probably need some type of high impedance device like a mosfet to go
between
the sensor and the LED.

--
Dan Hollands
1104 State Road
Webster NY 14580
585-703-2963
QuickScore@USSailing.net
www.QuickScoreRace.com
"stocky" <stocky@capri.net.au> wrote in message
news:uCRSa.7273$OM3.2658@news-server.bigpond.net.au...
I am building a speed switch around a LM2907, but want to add a
"pulse"
LED
that blinks every time the magnet goes past the senor....I'm having a
mental
blank, i'm sure it's easy but can't think how to do it! Should I
capacitively couple the signal from the sensor, so it doesnt mess up
the
signal goint to the '2907 and use something like a schmitt trigger to
flash
the LED? I know the output amplitude from the sendor varies greatly
with
speed, but I need the LED pulses to make it easy to setup. Ant
suggestions?


A schmitt trigger would be a good way you will set the on time (LED)
and at high speed the trigger would be so fast that you may not see it
and as you noted the input loading would be reduced.
Hope it helps