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Using a hard drive to build an anemometer

V

Vlad

Jan 1, 1970
0
I am using a discarded hard drive as the base of for an anemometer.
I have it running and can generate up to 200 mV a.c. that are ( I
assume) proportional to the wind speed.
The motor has 4 connections to the outside and I can get approximately
the same a.c. voltage from any combination of pairs.
My question is:
Can I use some type of combination ( delta, star etc.) that would
increase the generated voltage?
This connects to a high impedance circuit that converts the a.c. or
d.c. to RS232.
A computer plots the result.

Thanks for the help

Vlad
 
W

Wim Ton

Jan 1, 1970
0
Vlad said:
I am using a discarded hard drive as the base of for an anemometer.
I have it running and can generate up to 200 mV a.c. that are ( I
assume) proportional to the wind speed.
SNIP

Maybe an idea for the computer recycling competition organized by the German
publisher Heise (www.heise.de)

Wim
 
R

Roger Lascelles

Jan 1, 1970
0
The trouble with your tachometer is that output voltage is proportional to
speed. I have played with such tachometers and found it hard to come up
with a reliable pulse detection over the large speed range of > 100 : 1 you
need for wind speed.

The opto and hall effect types are easier to use, because they have a signal
which is constant with speed. Personally, I would drill a circle of holes in
the disc and put a LED and phototransitor on either side of the disc - now
you have digital level transitions ready to go into a schmitt trigger (40106
or 74HC14 etc) and then into your microprocesor.


Some thoughts on using the motor windings :

Because the signal is proportional to speed, I would feed it into a filter
with diminishing gain as frequency increases - ie an integrator response.
That will give you a flat overall response. That means an awful lot of gain
at low frequencies. You will have to stop increasing gain below some low
frequency or will just have rubbish noise as output.

A schmitt trigger after the filter will give you pulses ready to feed to a
microprocessor. Some microprocessor smarts may be needed to reject random
transitions at very low speed.

Have you thought of sending the pulses straight down the wire with no RS232
needed ?

Roger
 
N

Nicholas O. Lindan

Jan 1, 1970
0
Roger Lascelles said:
The trouble with [using a HDD motor as a] tachometer is that output voltage
is proportional to speed. I have played with such tachometers and found it
hard to come up with a reliable pulse detection over the large speed range
of > 100 : 1 you need for wind speed.

Forward into the past:

Sounds like a dose of FM radio is needed: Amplify the piss out of it and
let it clip and clamp so you get a variable frequency square wave.

Of you can use an AGC circuit ...

A PIC, though, will do you no good.
The opto and hall effect types are easier to use, because they have a signal
which is constant with speed.

I take it you meant "a signal [whose amplitude] is constant with speed."

Depending on the age of the disk drive there may be a hall-effect tachometer
pick-up built into the motor. If it is really old there will be an aluminum
ring with slots in it ... with a phototransisor and an incandescent lamp ...
Have you thought of sending the pulses straight down the wire with no RS232
needed ?

Second this suggestion. With luck you will only have two wires coming from
the anemometer with no (almost no) active circuitry up there on the mast.
 
R

Rich Grise

Jan 1, 1970
0
Roger Lascelles said:
The trouble with [using a HDD motor as a] tachometer is that output voltage
is proportional to speed. I have played with such tachometers and found it
hard to come up with a reliable pulse detection over the large speed range
of > 100 : 1 you need for wind speed.

Forward into the past:

Sounds like a dose of FM radio is needed: Amplify the piss out of it and
let it clip and clamp so you get a variable frequency square wave.

Of you can use an AGC circuit ...

A PIC, though, will do you no good.
The opto and hall effect types are easier to use, because they have a signal
which is constant with speed.

I take it you meant "a signal [whose amplitude] is constant with speed."

Depending on the age of the disk drive there may be a hall-effect tachometer
pick-up built into the motor. If it is really old there will be an aluminum
ring with slots in it ... with a phototransisor and an incandescent lamp ...
Have you thought of sending the pulses straight down the wire with no RS232
needed ?

Second this suggestion. With luck you will only have two wires coming from
the anemometer with no (almost no) active circuitry up there on the mast.

If you're going to do that, a fifteen cent magnet and reed switch would do
it.

Good Luck!
Rich
 
R

Roger Lascelles

Jan 1, 1970
0
Nicholas O. Lindan said:
Sounds like a dose of FM radio is needed: Amplify the piss out of it and
let it clip and clamp so you get a variable frequency square wave.

Of you can use an AGC circuit ...

The trouble is at low frequencies. Imagine a very low amplitude 1 Hz
waveform. You amplify it and clip it. Thus at the waveform zero crossover
points, you have a high gain amplifier with input moving slowly through the
active range. The output will slam up and down according to bearing wobble,
noise, you name it - just like an FM limiter does with no signal. Means
that simple edge counting won't give you speed. A micro could work out the
difference between long cycles with bouncing edges vs short cycles.

The integrator slows down the low frequencies and does help. I have played
with this stuff and though it can be tamed, I reckon its too much trouble
for a one-off.

The beauty of the Hall / Opto approach is that the analog signal increases
smoothly as the magnetic field / light builds up and diminishes, so a simple
schmitt cleanup does the job.

The reed switch suggested in another reply has been used a lot. A small
reed switch will do > 1 KHz !! which for 10cm cup spokes is about 628 metres
per second or 2261 km / hr !! The reed switch does bounce, but the bounce
is fairly consistent across the speed range and you get a nice hysteresis
built in. Only 2 wires needed.

Roger
 
F

Fred Bartoli

Jan 1, 1970
0
Nicholas O. Lindan said:
Roger Lascelles said:
The trouble with [using a HDD motor as a] tachometer is that output voltage
is proportional to speed. I have played with such tachometers and found it
hard to come up with a reliable pulse detection over the large speed range
of > 100 : 1 you need for wind speed.

Forward into the past:

Sounds like a dose of FM radio is needed: Amplify the piss out of it and
let it clip and clamp so you get a variable frequency square wave.

Of you can use an AGC circuit ...

A PIC, though, will do you no good.

Hmmm...
 
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