Double RPM output

StickyVelvet · Post by **StickyVelvet** » Fri Feb 13, 2004 9:40 pm

I've just bought a Zalman 7000A AlCu. Unfortunately, because of the low RPMs that it runs at, QFan on my ASUS A7N8X Deluxe fails to operate. What I want to do is double the RPMs going into the motherboard, so that then QFan will work. I figure I just need to make a little circuit which mixes the fan's tacho signal with itself, but after several hours of scouring the net I've failed to find anything handy. So, can anyone point me in the direction of some schematics, instructions, tips or anything which would help me to build a simple frequency mixer?

This seems the sort of thing that I'm sure has been done already, but like I say, I can't find it.

lenny · Post by **lenny** » Fri Feb 13, 2004 10:52 pm

Googling for "frequency doubler" got me this:

http://pdfserv.maxim-ic.com/en/an/tb32.pdf

However' googling for DS1035 shows that it delays output for up to 30 ns, suggesting that you're going to need a hell of a lot of them for fan tach signals

Perhaps the same idea with a bunch of slower delays?

Edit : removed comment to Trip coz he deleted his post

Trip · Post by **Trip** » Sat Feb 14, 2004 1:19 am

lenny wrote:
Edit : removed comment to Trip coz he deleted his post

heh, yea I misread the original post. I thought he wanted to overvolt his fan... (which I don't think is possible with a regular PSU)

silvervarg · Post by **silvervarg** » Sat Feb 14, 2004 11:05 am

I think the following schema will work.
It uses a single IC chip with at least 3 XOR in it.
For instance the chip 74HC136 (~$0.50) should do fine.

Code: Select all

      |-------------------
V+ --------               |---
           )XOR-----          )XOR---- FAN_Tach*2
FAN_Tach --         )XOR------
         |----------

The first XOR just gives you the inverted signal.
The second XOR gives you a positive signal with spikes down on every flank, so the signal is double in frequency.
The third XOR just inverts the signal again so you get only short positive spikes, like the tach input on the motherboard expects.
You need resistors to limit the current. If you need a longer pulse you could add a capacitor to stretch the pulse.
[/code]

Vegita · Post by **Vegita** » Sat Feb 14, 2004 6:25 pm

I have an ASUS mobo too and it also kicked me into BIOS setup because the CPU HSF rpms were too low.

What I did was set it to ignore the HSF rpm... don't know if that's the best solution.

What is this QFan thing anyway?

Trip · Post by **Trip** » Sat Feb 14, 2004 7:30 pm

couldn't you just use a 4 to 3 adapter

zalman fanmate

HSF?

lenny · Post by **lenny** » Sat Feb 14, 2004 8:03 pm

Then it would say 0 rpm = fan failure.

Trip · Post by **Trip** » Sat Feb 14, 2004 8:22 pm

it has to have a RPM readout? that's crazy.

all asus boards aren't like that are they?

StickyVelvet · Post by **StickyVelvet** » Sat Feb 14, 2004 9:29 pm

QFan is a system that some ASUS motherboards have which controls the speed of the CPU Fan. In the BIOS, you can specify the fan speed, but if the CPU gets hotter than 50C, then it ramps up the fan until it cools back down. Simple but nice. I was using this with the stock HSF that I had until last week when I got my Zalman 7000A. The problem is that for some stupid reason QFan doesn't work properly with slow fans (just QFan - everything else is fine). I figure if I fool it into thinking the fan is going twice as fast as it really is, then the system should work fine.

I'm currently using the Zalman in series with the Fan Mate 1 and with QFan switched off. If I set the Fan Mate to minimum (*manually*, what a hassle), then the CPU temps are fine (mid-40s) until I load the CPU when it rockets to as much as 57C. This was yesterday when the ambient room temp was 31C. Probably the worst it'll ever get where I live.

In any case, I know exactly what my hardware can do, and am trying to get around the limitation of QFan.

silverarg, I've had a think about your circuit, and I might give it a go. Thanks. But doesn't it depend on the lag of the XOR gates? And the pulses won't be evenly spread out, but that might not matter ... I'll probably try to give it a go in the next week or so, but in the meantime I'm open to more ideas!

ahrbruz · Post by **ahrbruz** » Sat Feb 14, 2004 11:35 pm

I've been there!

I'm running a Zalman 7000A AlCu at 5V courtesy of a 5V lead from my Zalman PSU. I've modded the CPU fan lead by pulling the 'tach' lead (yellow wire) and attaching it to a spare molex which is plugged in to the mobo CPU fan header.

The CPU fan is running +/- 1100 rpm at the following temps:

CPU: 36 degrees C
RAM: 27 "
Case: 23.7 "

Temps are on dedicated sensors as the Asus sensors are unreliable.

Post by **Ralf Hutter** » Sun Feb 15, 2004 7:33 am

Trip wrote:it has to have a RPM readout? that's crazy.

all asus boards aren't like that are they?

Most motherboards have a "CPU fan failure" setting in the BIOS, but the vast majority of them also have the ability to disable this setting. All you need to do is have it hooked up correctly the first time you go into the BIOS so you can disable it. After that you don't need to have any rpm output at the CPU fan header.

lenny · Post by **lenny** » Sun Feb 15, 2004 5:25 pm

Ralf / Trip, StickyVelvet says that he wants QFan, which is why fan monitoring cannot be disabled. I haven't tried QFan myself so I can't say, but I'm willing to take his word for it. His solution is actually pretty elegant - just double the RPM and fool the BIOS. You can always adjust the divider in MBM to get the correct reading if you need to know.

Alternatively, if QFan will work without a tach signal (as opposed to a low tach signal - sounds crazy, but engineers are not always logical), then just remove the RPM lead (the one that's not red or black).

ruprag · Post by **ruprag** » Mon Feb 16, 2004 5:16 am

StickyVelvet , I fail to see why you need QFan if your temperatures only go up to 57 with 31 ambient !!

The AMD chips are rated 85 safe operating temp so

btw. I currently have 52 idle and 63-4 when running burn (I had a bit lower temp but then I had to fiddle

) I am not very comfortable with this but since it is stable I try not to worry

)

bomba · Post by **bomba** » Mon Feb 16, 2004 7:13 am

Try speedfan,
It's free, does the same thing as Q-Fan and more, and on my ASUS P4P800dlx motherboard, works just fine with the Zalman 7000.

Joe DeFuria · Post by **Joe DeFuria** » Mon Feb 16, 2004 7:33 am

bomba wrote:Try speedfan,
It's free, does the same thing as Q-Fan and more, and on my ASUS P4P800dlx motherboard, works just fine with the Zalman 7000.

Quickie questoin for you: I have the same mobo and have only been able to control the fan speed coming off the CPU Fan header. Have you been able to control fans connected to the Chassis and/or power supply header?

fancontrol · Post by **fancontrol** » Mon Feb 16, 2004 1:04 pm

StickyVelvet wrote:What I want to do is double the RPMs going into the motherboard, so that then QFan will work.

you've really got two options. if you just want the motherboard to know the fan is turning, you could make a oscillator that spits out a fixed frequency with a kind of watchdog on the fan tach output. Not easy, but not bad.

if you really want to double the frequency of the tach output, you'll need a micro or pld that measures the period between the last two pulses and inserts one 1/2 of the period after the last tach pulse. we used a trickier version of that to spit out an arbitrary multiplier of an input clock for some tests around here. a semi-bogus way to do this is to insert a pulse a fixed time after the existing pulses from the tach. could make for messy readings, though.

a third option, if it's available, is to tell your motherboard that the fan only spits out one pulse per revolution.

Toth · Post by **Toth** » Mon Feb 16, 2004 1:35 pm

silvervarg wrote:I think the following schema will work.
It uses a single IC chip with at least 3 XOR in it.
For instance the chip 74HC136 (~$0.50) should do fine.
Code: Select all
      |-------------------
V+ --------               |---
           )XOR-----          )XOR---- FAN_Tach*2
FAN_Tach --         )XOR------
         |----------
The first XOR just gives you the inverted signal.
The second XOR gives you a positive signal with spikes down on every flank, so the signal is double in frequency.
The third XOR just inverts the signal again so you get only short positive spikes, like the tach input on the motherboard expects.
You need resistors to limit the current. If you need a longer pulse you could add a capacitor to stretch the pulse.
[/code]

That won't work, unless I'm mistaken. The first XOR gate will give the inverted FAN_Tach signal as you said. But then you're XOR'ing the inverted tach signal with the original tach signal which will always produce a high signal. You are then XOR'ing that with +V, High XOR High will always give you a low signal.

silvervarg · Post by **silvervarg** » Mon Feb 16, 2004 1:38 pm

Fancontrol:
if you really want to double the frequency of the tach output, you'll need a micro or pld that measures the period between the last two pulses and inserts one 1/2 of the period after the last tach pulse.

So, what you are saying is that the motherboard will not recognice the speed if the pulses are not evenly spread?
If that is true my suggestion for a quick fix that generated a short pulse on each flank won't work. Too bad, it would have been a neat trick for less than $1.

Double RPM output

Double RPM output

Speedfan?

Re: Speedfan?

Re: Double RPM output