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'[EE]: Variable Reluctance Sensor'
2000\11\09@104045 by Ken Godee

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Maybe I'm just going about this the wrong way?
I'm using a 16C63 and 10ms sample time for the sensor.
I'm using a Variable Reluctance Sensor with its output tied thru
a National LM2907 Frequency to Voltage Converter. The LM2907
will convert sensor output to a square wave at a steady dc voltage,
but the problem I'm having (I think) is the LM2907's output,
low out min. = 25% of supply current
high out max = 75% of supply current
The way I see it is this is producing;
5vdc supply current=
PWM output from LM2907
9ms period 30% duty cycle, peak=3.75vdc, low=1.25vdc
= aprx. 2vdc steady. This is of coarse very or too close to what I
figure the 16C63 will see it's pin state, I figure right around 1.3vdc
where the 16C63 will see changed state. Square wave looks clean
and works until I exceed 100hz. Uping supply current is possible
but then raises the low to high.
Sensor output in the 1vac/200hz (0-2vac/0-400hz) range.
I'm SURE there is a easier way to convert the sensors signal, I do
not have to use the LM2907. If someone could point me in a
direction to get me off this hamster wheel I would be indebted.






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2000\11\09@113418 by Arthur Brown

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Ken
how have you got pins 2 - 3 of the LM2907

1. vdd cap to pin2. then vdd zenner k to pin3.
freq out is 2x input pulse height = zenner

or

2. vdd 50k to pin2.pin3 cap from pin 3 to vdd.
Vout = 1/2 Vcc

we used the LM2907 about 25 years ago 1975abt.
if you need to to remove the offset use an opamp at the output of the
LM2907.
there was another device LM2917 that gave an output that was independent of
supply voltage.

Regards Art

----- Original Message -----
From: Ken Godee <spam_OUTkenTakeThisOuTspamPERFECT-IMAGE.COM>

> but the problem I'm having (I think) is the LM2907's output,
> low out min. = 25% of supply current
> high out max = 75% of supply current

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2000\11\09@125338 by Ken Godee

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Art,
Thanks for your response.
What your describing below is their "one shot" and
"two shot" zero crossing config, I've hacked around on both
configs and still having probs.
What sounds interesting in their app note (AN-162 pg.13) they say
you can create a full output swing in a one shot config "by
reducing or removing the negative feedback around the op amp."
which I thought would be the loop back from pin 4 to pin 7.
But I guess I can't figure their statement because reducing or
removing the loop does not create a full output swing.
I also have a LM2917 that I'll mess with next and also have a
sample of their LM1815 "Adaptive Variable Reluctance Sensor
Amplifier" on its way to mess with. As you can tell there is alot
of messing going on. The op amp on the output is another choice
to try. Just trying to keep part counts down etc., and also trying to
find out if this is the most efficient way to interface the sensor?
Thanks again.

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