tachometer square voltage value for pc fans

[maxmax80]

Hi I'm Max from Italy!


I've seen on your site and I hope you can answer me!


I need to split the rpm speed signal of my CPU fan, and I've split it (a branch to the mother board and other branch to an external rheobus) with a simple cable,
but the reading value from the mother board is 0 rpm and on rheobus value is lower than the real value.

I think it is because splitting the signal, the square wave tachometer is halved, and not having sufficient amplitude so it is impossible to read correctly.

I must therefore amplify this wave, but not want to amplify it too much, to avoid burning the mother board!

So, I ask you technical information on the internet can not be found:
what is the peak voltage of square wave that corresponds to tachometer signal state " 1 " that travels on the yellow cable?




thanks

max -italy-

 

[Reloadron]

Hi Max

OK, I am not 100% what you have in mind but I think you are looking to use the tachometer output of your CPU fan. Just about all fans in computers including the CPU fan that have a tach output have what is known as an open collector output so the actual amplitude of the output pulses is a function of a pullup resistor on the motherboard. The best way to observe these pulses is using a scope. Typically a fan outputs two pulses per revolution of the fan. Typically they are 5 volt pulses but again it is a function of the motherboard. This link provides a good overview of the newer 4 wire fan design.

Is your fan a 3 wire or 4 wire configuration and what exactly are you trying to get done?

CIAO
Ron

 

[maxmax80]

Hi Ron!

I have a pci rehobus, Sunbeam theta ( Sunbeam Theta USB Fan controller )
I use it only to monitor rpm of my case fans (by connect only yellow cable, not black & red cable in 3 pin connectors)

well, to use pwm mobo control for cpu cooler fan I use Nanoxia Pwmx controller ( **broken link removed** )
that it convert 3 pin tacho to 4 pin pwm, and he allows (at the same time) the mother board display rpms / pwm correctly..
so I opened the pwmx and -on out yellow cable- I settled another cable to run tacho signal to sunbeam theta..
and behold, when I connect it happens what I said in previous post, but when I unplug sunbeam, the mother board takes to read the rpm normally

tachometer signal is generated by the fan and the motherboard simply reads it, right?
or there is a send-return trade from fans to motherboard yellow cable?

I think the signal divided in half does not like neither the mother board nor the sunbeam..


ciao

max

 

[Reloadron]

I think the signal divided in half does not like neither the mother board nor the sunbeam..

That would be my guess too. Since the output from the fan is what we call open collector it depends on the motherboard to make the pulses. Thus the problem. If the other unit also tries to do what the motherboard does and uses its own pull up there will be a problem.

CIAO
Ron

 

[maxmax80]

Since the output from the fan is what we call open collector it depends on the motherboard to make the pulses. Thus the problem. If the other unit also tries to do what the motherboard does and uses its own pull up there will be a problem.

CIAO
Ron

I'm not sure about it because the other case pwm fans are guided by CoolerMaster WindRider ( **broken link removed** )
It send back the rpm fans by multiple cable formed by only yellow cables!
I try to connect these signle cables at sunbeam theta and It can read rpm correctly!!

for this reason I think I can do the same by cpu PWMX controller to sunbeam theta, but I need to know exact mvolt (or volt) value of tachometer quare signal!


thanks

max

 

[maxmax80]

is likely that I need not amplify the signal,
but I manage using a simple LM358 as volt signal buffer
(1:1 gain does not amplify anything so there is a risk of burn anything)
which is a single-supply dual operational, and then I put one on a branch to mother board and one a branch to sunbeam theta, and let 's see if it works ...

I can do it Vcc power supply by floppy cable!

do you think I must use +5v or +12v on floppy cable?

thanks

max

 

[maxmax80]

That would be my guess too. Since the output from the fan is what we call open collector it depends on the motherboard to make the pulses. Thus the problem. If the other unit also tries to do what the motherboard does and uses its own pull up there will be a problem.

CIAO
Ron

I put an LM358 ( two independent high gain operational amplifiers) in the circuit with single power supply 12volt by floppy cable whitout any others component s

I use it simply like buffer/voltage follower because the output voltage return to the input voltage "-"

but now sunbeam read fix 720 rpm and mother board read a random value from zero to 7250 rpm (that not correspond a real change of fan velocity)

the way is correct, but what kind of component () and where I can put (resistor, capacitor, diode) to restore stability?

thanks

max