I recently purchased a small fan (40mm square, 12v dc) to mount in a
temperature sensor housing in order to ventilate the sensors. I assume the
fans are normally used in a computer.

There are three wires coming out of it, red, black, and yellow I assume the
red and black are + and - 12v. What is the yellow for? is it some kind of
pulsed output to enable one to control the speed? if so how is it usually
done? some kind of diode pump arrangement perhaps?

Don

Donwill coughed up some electrons that declared:

I recently purchased a small fan (40mm square, 12v dc) to mount in a
temperature sensor housing in order to ventilate the sensors. I assume
the fans are normally used in a computer.

There are three wires coming out of it, red, black, and yellow I assume
the red and black are + and - 12v. What is the yellow for? is it some kind
of pulsed output to enable one to control the speed? if so how is it
usually done? some kind of diode pump arrangement perhaps?

Don

It is the tacho line - open collector arrangement I believe.

So feed it with a small current from a pullup resistor and you should get
pulses proportional to RPM.

There's a 4 wire fan too - the 4th wire controls fan speed.

There are some diagrams here that may be of interest:

http://www.bearblain.com/fan_speed_control.htm

Cheers

Tim

It is the tacho line - open collector arrangement I believe.

So feed it with a small current from a pullup resistor and you should get
pulses proportional to RPM.

There's a 4 wire fan too - the 4th wire controls fan speed.

There are some diagrams here that may be of interest:

http://www.bearblain.com/fan_speed_control.htm

Cheers

Tim

Many thanks Tim the link is very useful. The sensor housing is going to be
installed in a not yet built conservatory, I was going to drive the fan with
the aid of a 1Watt 12V solar panel which is going to be installed in the
roof of the conservatory.
I wondered if the yellow lead was some kind of speed indication and if so,
the output would be related in some way to solar radiation intensity and
could therefore be used to control an automatic watering system for when we
are on holiday; it would be more accurate than a timed system I think.
I will have to integrate the pulses by some, as yet undetermined means to
enable a timed valve opening for watering.

Time to get the old scope out I think. :-)

Cheers and thanks
Don

Thanks again

"Donwill" popple @diddle .dot wrote in message
...

..
I wondered if the yellow lead was some kind of speed indication and if so,
the output would be related in some way to solar radiation intensity and
could therefore be used to control an automatic watering system for when
we are on holiday; it would be more accurate than a timed system I think.
I will have to integrate the pulses by some, as yet undetermined means to
enable a timed valve opening for watering.

If you are going to build something why not make it a soil moisture meter
and get a direct reading of when to water?

A couple of bits of noncorrosive wire stuck to a plant label should do for
the sensor.

In article ,
"Donwill" popple @diddle .dot writes:

Many thanks Tim the link is very useful. The sensor housing is going to be
installed in a not yet built conservatory, I was going to drive the fan with
the aid of a 1Watt 12V solar panel which is going to be installed in the
roof of the conservatory.
I wondered if the yellow lead was some kind of speed indication and if so,
the output would be related in some way to solar radiation intensity and
could therefore be used to control an automatic watering system for when we
are on holiday; it would be more accurate than a timed system I think.
I will have to integrate the pulses by some, as yet undetermined means to
enable a timed valve opening for watering.

Time to get the old scope out I think. :-)

You get two pulses per rev for the original tacho driven ones.
Some also have a self-heating thermister in the airflow, and if
the airflow isn't cooling the thermister (e.g. fan running but a
blocked filter), they fake a lower speed. (I guess they start
removing some pulses, because with better sense analysis circuits,
you can tell that the fan is running at full speed but the airflow
has been lost, but I don't have one of those to hand to check out
exactly how it signals this).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

"Andrew Gabriel" wrote in message
.. .
In article ,
"Donwill" popple @diddle .dot writes:

Many thanks Tim the link is very useful. The sensor housing is going to
be
installed in a not yet built conservatory, I was going to drive the fan
with
the aid of a 1Watt 12V solar panel which is going to be installed in the
roof of the conservatory.
I wondered if the yellow lead was some kind of speed indication and if
so,
the output would be related in some way to solar radiation intensity and
could therefore be used to control an automatic watering system for when
we
are on holiday; it would be more accurate than a timed system I think.
I will have to integrate the pulses by some, as yet undetermined means to
enable a timed valve opening for watering.

Time to get the old scope out I think. :-)

You get two pulses per rev for the original tacho driven ones.
Some also have a self-heating thermister in the airflow, and if
the airflow isn't cooling the thermister (e.g. fan running but a
blocked filter), they fake a lower speed. (I guess they start
removing some pulses, because with better sense analysis circuits,
you can tell that the fan is running at full speed but the airflow
has been lost, but I don't have one of those to hand to check out
exactly how it signals this).


The last time I saw a machine that detected lack of airflow it used a cup in
the airflow that acted against a microswitch.
Simple and fairly reliable.

In article ,
"dennis@home" writes:
The last time I saw a machine that detected lack of airflow it used a cup in
the airflow that acted against a microswitch.
Simple and fairly reliable.

What you care about is the cooling ability, which is what the
thermistor measures directly, and it's a technique which is present
in some kit I had which dates from 1970's (although not integral
with the cooling fan back then).

I've never seen what you describe used. It fails to measure the
cooling ability (e.g. if you're drawing in hot air, it will not
notice that there's no cooling). Also, forced air paths are prone
to dust build-up, and such a device could well end up getting
stuck in position after a few years running and dust build up,
and wouldn't come close to the reliability required in most
commercial computer kit. Even back in the 1970's, the cost of
the mechanical part to do this would way exceed the cost of
what is a very simple and much more effective thermistor circuit.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Donwill has brought this to us :

It is the tacho line - open collector arrangement I believe.

So feed it with a small current from a pullup resistor and you should get
pulses proportional to RPM.

There's a 4 wire fan too - the 4th wire controls fan speed.

There are some diagrams here that may be of interest:

http://www.bearblain.com/fan_speed_control.htm

Cheers

Tim

Many thanks Tim the link is very useful. The sensor housing is going to be
installed in a not yet built conservatory, I was going to drive the fan with
the aid of a 1Watt 12V solar panel which is going to be installed in the roof
of the conservatory.
I wondered if the yellow lead was some kind of speed indication and if so,
the output would be related in some way to solar radiation intensity and
could therefore be used to control an automatic watering system for when we
are on holiday; it would be more accurate than a timed system I think.
I will have to integrate the pulses by some, as yet undetermined means to
enable a timed valve opening for watering.

Time to get the old scope out I think. :-)


Poke a couple of stainless steel probes in the soil, connect to an
op-amp, then arrange the op-amp to turn a solenoid valve on when the
conductivity between the probes falls - simples.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On 29 July, 17:25, Harry Bloomfield
wrote:
Donwill has brought this to us :





It is the tacho line - open collector arrangement I believe.

So feed it with a small current from a pullup resistor and you should get
pulses proportional to RPM.

There's a 4 wire fan too - the 4th wire controls fan speed.

There are some diagrams here that may be of interest:

http://www.bearblain.com/fan_speed_control.htm

Cheers

Tim

Many thanks Tim the link is very useful. The sensor housing is going to be
installed in a not yet built conservatory, I was going to drive the fan with
the aid of a 1Watt 12V solar panel which is going to be installed in the roof
of the conservatory.
I wondered if the yellow lead was some kind of speed indication and if so,
the output would be related in some way to solar radiation intensity and
could therefore be used to control an automatic watering system for when we
are on holiday; *it would be more accurate than a timed system I think.
I will have to integrate the pulses by some, as yet undetermined means to
enable a timed valve opening for watering.

Time to get the old scope out I think. :-)

Poke a couple of stainless steel probes in the soil, connect to an
op-amp, then arrange the op-amp to turn a solenoid valve on when the
conductivity between the probes falls - simples.

--
Regards,
* * * * Harry (M1BYT) (L)http://www.ukradioamateur.co.uk

No power required, UK invention

http://www.autopot.co.uk/home.php?droplet=welcome

Adam

Tim S wrote:
Donwill coughed up some electrons that declared:

I recently purchased a small fan (40mm square, 12v dc) to mount in a
temperature sensor housing in order to ventilate the sensors. I assume
the fans are normally used in a computer.

There are three wires coming out of it, red, black, and yellow I assume
the red and black are + and - 12v. What is the yellow for? is it some kind
of pulsed output to enable one to control the speed? if so how is it
usually done? some kind of diode pump arrangement perhaps?

Don

It is the tacho line - open collector arrangement I believe.

So feed it with a small current from a pullup resistor and you should get
pulses proportional to RPM.

There's a 4 wire fan too - the 4th wire controls fan speed.

There are some diagrams here that may be of interest:

http://www.bearblain.com/fan_speed_control.htm

Cheers

Tim

Many thanks Tim the link is very useful. The sensor housing is going to be
installed in a not yet built conservatory, I was going to drive the fan
with
the aid of a 1Watt 12V solar panel which is going to be installed in the
roof of the conservatory.
I wondered if the yellow lead was some kind of speed indication and if so,
the output would be related in some way to solar radiation intensity and
could therefore be used to control an automatic watering system for when we
are on holiday; it would be more accurate than a timed system I think.
I will have to integrate the pulses by some, as yet undetermined means to
enable a timed valve opening for watering.

Time to get the old scope out I think. :-)

Cheers and thanks
Don

In message , Donwill wrote
, I was going to drive the fan with
the aid of a 1Watt 12V solar panel which is going to be installed in the
roof of the conservatory.

I will have to integrate the pulses by s
ome, as yet undetermined means to
enable a timed valve opening for watering.

Would the fan stop every night when it gets dark and hence you would
zero pulses?
--
Alan
news2009 {at} admac {dot} myzen {dot} co {dot} uk