if the fan gives an RPM reading then it will prodice an oscillation, if however, as Cyril mentioned, it only detects weather the fan is either running or not running, then it will be even easier for you to fool the fan sensor.
Slow here at work tonight so I breadboarded the 555 oscillator circuit that Cal sent you.
I believe it will work just fine for you. Thought you would be able to just plug it right into your fan header but that is not going to work.
It probably has something to do with the Frequency selected but at 12V the frequency is not stable and runs away until it hits around 800hz. The good news is if you select a +VCC of 5V the circuit works perfectly and gives a steady output of 100hz gnd pulses if you remove RL.
C=0.1uF RA=47Kohm RB=47Kohm and the capacitor that is marked 10 to 100uf will work with either. I tried both.
After you build your circuit I would try it out with a speaker first to make sure it works. Just connect it where it shows RL. The speaker should emit a low frequency hum just slightly higher than powerline hum.
Once the circuit is working remove RL(speaker) and the wire used to hook in the speaker. Connect O/P to the signal pin for the fan on the video card. Connect +VCC to a 5V wire and gnd to a gnd wire. There you have it.
If you do not feel capable of building the circuit yourself a budding Electronic Wizard at your local community College would probably do it for a few pints.
[This message has been edited by cyril1 (edited 06-21-2001).]
I thought it would be seen as a boring question and get ignored.
I will try to find out what signal the card is getting from the fan but I would assume it is just a normal fan, (as it is not made by Asus).
If I'm wrong on this let me know but I think it works in a similar way to a crankshaft or ABS sensor which gives and induced "pulse" or many "pulses" per revolution.
I'd also guess it does this with the negative side. So the fan has +12v and Ground supply going in to the motor. One of these will give a fluctuating AC voltage down the rotation wire. I could therefore check this with a voltmeter?? just to see if this is the case.
That's the old v7700 Smart Doc app that didn't have ram temp monitoring. It was just already up on my site and I couldn't remember the file name of the V8200 image at the time. Laziness really
The Molex connector has three wires: + (usually 12V, usually red), GND (usually black), and SIGNAL (usually yellow or white, but there are no clear standards). Unless you are a board designer, only the + and GND wires are of interest to you. (For the curious: The SIGNAL switches between NC and GND twice per rotation, resulting in a square periodical signal if you connect a (low) voltage.
According to this statement the fan connection only supplies ground or open and not a voltage. This most likely means the voltage is supplied from the mainboard through a pull up resistor. If this is the case then the 555 circuit with the values I supplied should work perfectly. Just omit the load resistor.
Unfortunately a voltmeter will probably not work too well as it will average everything. You really need a scope to tell if anything is comming from the fan.
The best use for the voltmeter would be to disconnect the fan, power up the PC and check to see if there is a voltage on the pin that the signal wire would connect to. This voltage would be a steady DC voltage.
If the voltage is there then the circuit without a load resistor would work perfectly since the it would pull up to whatever voltage is there and twice per revolution it would go to ground at a 100hz rate. ie 6000rpm.
[This message has been edited by cyril1 (edited 06-21-2001).]
I'm out of my depth here but I take the explanation to mean the fan returns a, (varying according to fan speed) pulsed negative voltage (A/C) with the ground supplied to the fan from the ground header pin on the card (lets call it -12v for discussions sake although it's not the correct term).
So what I would need is an oscillated -12v to the rotation pin header. what I'm not sure of is whether this ground "voltage" needs to be from the -12v pin on the card or could be from -12v out of a four pin plug?
Like I said it's over my head really and I'll struggle to build anything without a detailed circuit diagram & component description.
I'll go a see what I'm getting on the fan rotation pin
Look at the fan connector plug. It should have a red wire(12V) a black wire(gnd) and a yellow or white wire (signal) at least according to the info you supplied in your post above.
Unplug the fan and measure between where the black wire would have been and where the white or yellow wire would have been. Is there a DC voltage there when the PC is on?
If there is what is the voltage? I suspect there is a voltage there that is provided by a resistor on the board. The purpose of it is to keep a high on the input to the fan detection cct. If the cct never detects a low or has a high or a low all the time it alarms.
What the fan most likely does is supply a gnd twice per revolution to pull that voltage to gnd. In essence it makes a square wave of positive and gnd pulses.
----- ----- ----- +V
----- ----- ----- GND
Just pretend that looks like a square wave above. That might look like AC to the layman but it is actually ocillating dc. It is either off or on but never changes direction.
If you measure a positive DC voltage there then the 555 circuit using the values I supplied should work.
That was supposed to look like a square wave above but for some reason after I posted, it got compressed.
[This message has been edited by cyril1 (edited 06-23-2001).]
hmm ive been thinking, when my watercooling stuff arrives (if it ever does) I will be faced with the same problem, I suppose I could cheat and use a small fan, but now theres a problem in hand... well I just CANT use a fan can I!!!. It probly wont be for a week or 2 but I'll have a go at sorting the pulse issue out and let you know what happens... if you hear a rather loud bang, it means I did it wrong
Thing is cyril, a voltmeter may not give an accurate reading as it will be pulsing, er then again, I suppose it HAS to be either 12V or 5V and maybe if its going at a fair old rate then the meter may well read a decent average, my card only has a 2 pin fan, but my board has a few 3 pin ones, If I get chance I'll get me scope out the loft an have a measure.
I think you are spot on with your last detailed description, It's just my understanding of it that was awry. I'm beginning to grasp it now.
I have checked the plug which was not easy considering how tiny it is. I cut up an old HDD jumper to make some female pins. (standard mobo 3pin plug shown in the pic for size).
Pin 1. red = +12v
Pin 2. rotation = +5.1v
Pin 3. Black = ground (-12v)
I then tried using another fan, (an Intel P3 retail), that has rotation detection. I powered it via a PSU 4 pin plug and connected the output rotation to the #2 pin on the Asus GF3 header (no other pin on the Asus card was connected). This worked showing fan speed in Smart Doctor, (all be it lower due to the slower rpm of the P3 fan).
I then removed this P3 fan and connected the multimeter to the #3 pin (ground) and the #2 pin rotation. Set the meter to ohms and used an air blow gun to spin the fan blades. (it had no power going to it at this time). This reported a varying meter reading related to fan speed.
So it looks as if it has the pull up resistor and is being supplied by the fan with a " Ground - NC - Ground - NC" etc... at a pulse speed dependent on fan revs.
It looks as if the 555 will do but I think I'll still need more help with the circuit layout/diagram to be able to buy the correct components and build It.
[This message has been edited by BladeRunner (edited 06-23-2001).]
I sent you an updated diagram of the Timer cct by e-mail. I am afraid I have no idea how to attach it here.
I am not sure if your e-mail provider will accept it since it is 5 Megs.
Maybe you can clue me in on how to attach pictures to a BBS. You obviously have a good handle on it.
Great pictures by the way. I am afraid to ask how much that Nikon cost.