Measuring RPM''s at relatively slow speeds.
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Thanks Smartdim, that is exactly what I was looking for.
Just curious, does it help at all to color the 'disk' part either all
white or all black? Would that improve the operation or should I just
leave well enough alone.
I think I should buy stock in DigiKey, I'm ordering weekly [noparse]:)[/noparse]
-John
John,
If you make a disk with many holes in it near the circumference of the
disk,
you can use an opto coupler to sense the rotation. The opto coupler is
basically a photo diode and a photo transistor. The photo diode shoots a
beam of
Infra Red light at the photo transistor. When the beam is blocked, the
photo
transistor is "off" and when the beam is not blocked the phototransistor
is
"on".....hence the holes in your disc will alternately block and not
block the beam.
You set the current in the photo diode part, much like you do for an
LED,
know the total voltage supply, know the forward voltage of the
photodiode, and
set the current using a resistor. Resistor value via ohms law.....270 to
330
ohms will do assuming a 5v supply.
The phototransistor section will be an NPN device. Emitter to ground,
collector gets a resistor to you supply voltage (if using stamp, then
5v). Resistor
value of 4.7k should work well. The base lead (if so equipped) should
get 1k to
ground to help the "turn off" time of the transistor.
You will sense the voltage at the collector. When the beam is blocked,
the
collector will read 5 volts, and when the beam is not blocked, ~ 0.2
volts.
These resistor values are simply off the top of my bald head.....but I
am
reasonably sure they will work.....
Write back if clarification or help is needed.
<A
HREF="http://dkc3.digikey.com/pdf/T032/1083.pdf">http://dkc3.digikey.com
/pdf/T032/1083.pdf</A>
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Just curious, does it help at all to color the 'disk' part either all
white or all black? Would that improve the operation or should I just
leave well enough alone.
I think I should buy stock in DigiKey, I'm ordering weekly [noparse]:)[/noparse]
-John
John,
If you make a disk with many holes in it near the circumference of the
disk,
you can use an opto coupler to sense the rotation. The opto coupler is
basically a photo diode and a photo transistor. The photo diode shoots a
beam of
Infra Red light at the photo transistor. When the beam is blocked, the
photo
transistor is "off" and when the beam is not blocked the phototransistor
is
"on".....hence the holes in your disc will alternately block and not
block the beam.
You set the current in the photo diode part, much like you do for an
LED,
know the total voltage supply, know the forward voltage of the
photodiode, and
set the current using a resistor. Resistor value via ohms law.....270 to
330
ohms will do assuming a 5v supply.
The phototransistor section will be an NPN device. Emitter to ground,
collector gets a resistor to you supply voltage (if using stamp, then
5v). Resistor
value of 4.7k should work well. The base lead (if so equipped) should
get 1k to
ground to help the "turn off" time of the transistor.
You will sense the voltage at the collector. When the beam is blocked,
the
collector will read 5 volts, and when the beam is not blocked, ~ 0.2
volts.
These resistor values are simply off the top of my bald head.....but I
am
reasonably sure they will work.....
Write back if clarification or help is needed.
<A
HREF="http://dkc3.digikey.com/pdf/T032/1083.pdf">http://dkc3.digikey.com
/pdf/T032/1083.pdf</A>
[noparse][[/noparse]Non-text portions of this message have been removed]
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject
and Body of the message will be ignored.
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http://docs.yahoo.com/info/terms/