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Looking for RPM circuit to read fan speed

J

Junkmail789

Jan 1, 1970
0
I'm looking for a circuit that would read the speed of a dc fan that runs at
5hz. I would like the speed indicated on 3 7 segment displays with a
decimal after the first digit. The circuit would need to be able to be
mounted on the shaft of the fan.

Can anyone point me in the right direction?

Would it be possible to design such a thing using a rotary encoder?

Thanks,

Matt S.
 
J

John Fortier

Jan 1, 1970
0
Junkmail789 said:
I'm looking for a circuit that would read the speed of a dc fan that runs at
5hz. I would like the speed indicated on 3 7 segment displays with a
decimal after the first digit. The circuit would need to be able to be
mounted on the shaft of the fan.

Can anyone point me in the right direction?

Would it be possible to design such a thing using a rotary encoder?

Thanks,

Matt S.

A mirror on the fan shaft, a reflector opto coupler and a counter circuit.
If you want more accuracy, use more mirrors. for example, with eight
mirrors at 5 Hz, you will get 40 counts per second. Assuming that by 5 Hz
you mean 5 revolutions per second.

From your description you seem to want to mount the whole circuit on the
shaft. Won't that, at 5 Hz, make it a bit difficult to read, unless you
grab the fan and swing round with it! So I'm assuming you only want the
sensor on the fan.

For the counter and display, there are purpose built modules available, at
relatively low prices.

Regards

John
 
J

Junkmail789

Jan 1, 1970
0
John,

I'll double check today but I believe there is a little bit of the shaft
protruding from the rear of the assembly. These are small fans (about the
size of those used in computer power supplies). So yes you are correct in
that I only want the sensor part on the shaft itself.

Thanks for the response, this is a great group :)

Matt S.
 
R

Rheilly Phoull

Jan 1, 1970
0
Junkmail789 said:
John,

I'll double check today but I believe there is a little bit of the shaft
protruding from the rear of the assembly. These are small fans (about the
size of those used in computer power supplies). So yes you are correct in
that I only want the sensor part on the shaft itself.

Thanks for the response, this is a great group :)

Matt S.
Then there was the old "shining a light through the fan blades intro an opto
transistor or device to your choice " trick ??
 
S

Spajky

Jan 1, 1970
0
I'm looking for a circuit that would read the speed of a dc fan that runs at
5hz.

on my site under electronics there is a schematics for non tach wire
PC fans adapter for measuring Rpm on computer, maybe can help that too
4 you before counter with display ...



-- Regards, SPAJKY
& visit site - http://www.spajky.vze.com
Celly-III OC-ed,"Tualatin on BX-Slot1-MoBo!"
E-mail AntiSpam: remove ##
 
J

John Fortier

Jan 1, 1970
0
Rheilly Phoull said:
5 available,
Then there was the old "shining a light through the fan blades intro an opto
transistor or device to your choice " trick ??

Assuming the blades don't overlap.

John
 
M

Michael A. Terrell

Jan 1, 1970
0
John said:
Assuming the blades don't overlap.

John

Then you set them at an angle to see between the blades.
 
W

Wade Hassler

Jan 1, 1970
0
Junkmail789 said:
I'm looking for a circuit that would read the speed of a dc fan that runs at
5hz. I would like the speed indicated on 3 7 segment displays with a
decimal after the first digit. The circuit would need to be able to be
mounted on the shaft of the fan.

Can anyone point me in the right direction?

Would it be possible to design such a thing using a rotary encoder?

Thanks,

Matt S.

Are there any disturbances on the power-supply leads that you could
read to determine the RPM?
(from one who avoids mechanical design)
 
C

Costas Vlachos

Jan 1, 1970
0
Wade Hassler said:
Are there any disturbances on the power-supply leads that you could
read to determine the RPM?
(from one who avoids mechanical design)



I think I've seen a typical app in one of Linear Tech's op-amp data sheets
which does exactly that. But I'm not sure what type of motor it is suitable
for. I think the rpm info should be present in the power lines, it's just a
matter of how easy it is to clean it up.

Smart idea!

Costas
 
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