splice 12v fan to pwm

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splice 12v fan to pwm

Unread post by spitefulmonkey » Wed Aug 14, 2019 4:16 pm

Is is safe to splice a 12v power source to use a 12v pwm fan on the boards header? Does a 12v fan use the same voltages in pulse and tach?

I'm assuming there is no bleed of the 12v line powering the fan over to either pulse or tach lines. So simply clipping the +5v and gnd lines and splicing them over to sata power should work?

My only worry was the tach line. I didn't want the fan pushing a high voltage back to the board. I suppose I could just clip the tach line. Aside from have a 0 rpm reading the speed control should still work.

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Re: splice 12v fan to pwm

Unread post by spitefulmonkey » Sat Aug 17, 2019 5:05 am

Well, the fan works fine this way. I have the gpio board arriving soon, then I plan on controlling fan speed via a python script reading actual cpu temps as opposed to the bios controlling it. Sense the temp sensor the bios uses is a ambient one near the cpu, this should work better I'd think. At any rate, will be fun to play.

Though not needed ,I still haven't found great info on reading the tach wire. Always open for input on how to read that without cooking any gpio pins.

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Re: splice 12v fan to pwm

Unread post by mad_ady » Sat Aug 17, 2019 1:52 pm

What gpio board?

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Re: splice 12v fan to pwm

Unread post by spitefulmonkey » Sat Aug 17, 2019 3:54 pm

mad_ady wrote:
Sat Aug 17, 2019 1:52 pm
What gpio board?
This one https://www.hardkernel.com/shop/16port-i2c-gpio-board/

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Re: splice 12v fan to pwm

Unread post by mad_ady » Sat Aug 17, 2019 8:45 pm

Thanks. Somehow I missed/forgot about this product

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Re: splice 12v fan to pwm

Unread post by odroid » Mon Aug 19, 2019 11:43 am

It looks dangerous.
Can you show us a connection diagram to minimize misinterpretation?

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Re: splice 12v fan to pwm

Unread post by spitefulmonkey » Mon Aug 19, 2019 2:09 pm

odroid wrote:
Mon Aug 19, 2019 11:43 am
It looks dangerous.
Can you show us a connection diagram to minimize misinterpretation?
For the fan? Currently I just have the blue pwm wire going to the motherboard from the fan. The positive and negative wires from the fan are spliced on to the 12v + (yellow) and - (black) wires from the sata power cable. The fans tach cable is not being used at the moment.

I just received my gpio board yesterday. Now what I will do is send the blue pwm wire from the fan to the gpio board (and not use the motherboards fan plug at all). I will write my own script to pulse the pwm signal to the fan thus controlling the speed myself via software. The script will monitor the cpu temps and adjust speed accordingly. The pwn line is 3.3v to 5v so the gpio will be fine as far as that goes.

The tach line was the only thing as I was uncertain of. Id like to feed that in through a gpio pin as well to read the pulses. 2 pulses to every full rotation on Noctua fans. It looks as though that line dumps 12v though. So I'll have to come up with something.

https://imgur.com/W2NUmNL

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Re: splice 12v fan to pwm

Unread post by odroid » Mon Aug 19, 2019 2:32 pm

If the PWM input voltage range is ~5V, it must be fine.

BTW, since the I2C-GPIO output port toggling speed is quite slow relatively, it seems to be very hard to implement the software driven PWM output.
So you need a I2C-PWM board something like this probably.
https://www.adafruit.com/product/815

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Re: splice 12v fan to pwm

Unread post by spitefulmonkey » Tue Aug 20, 2019 10:48 am

odroid wrote:
Mon Aug 19, 2019 2:32 pm
If the PWM input voltage range is ~5V, it must be fine.

BTW, since the I2C-GPIO output port toggling speed is quite slow relatively, it seems to be very hard to implement the software driven PWM output.
So you need a I2C-PWM board something like this probably.
https://www.adafruit.com/product/815
What is the speed on the gpio board? I only need 25kHz pulses for pwm control.

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Re: splice 12v fan to pwm

Unread post by odroid » Tue Aug 20, 2019 11:15 am

It seems to be very hard to switch an output port even at 10Khz due to 400Khz of I2C interface limitation.

But the hardest part is that keeping the constant switch frequency with reliable width-modulation because real time kernel might have over 2msec tolerance in the real world.

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Re: splice 12v fan to pwm

Unread post by spitefulmonkey » Tue Aug 20, 2019 2:51 pm

odroid wrote:
Tue Aug 20, 2019 11:15 am
It seems to be very hard to switch an output port even at 10Khz due to 400Khz of I2C interface limitation.

But the hardest part is that keeping the constant switch frequency with reliable width-modulation because real time kernel might have over 2msec tolerance in the real world.
On that note, a change of plans then haha. I am going to use a arduino "beetle" as opposed to the gpio board. It has pwm output in the range I need and i2c for communication. I have an extra one from a project I did (they are only $7 so I had bought extra). This should free up resources and be fun to do. Being a 5v board, is it ok to power it through the H2's 5v pin 2?

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Re: splice 12v fan to pwm

Unread post by spitefulmonkey » Tue Aug 20, 2019 2:56 pm

spitefulmonkey wrote:
Tue Aug 20, 2019 2:51 pm
odroid wrote:
Tue Aug 20, 2019 11:15 am
It seems to be very hard to switch an output port even at 10Khz due to 400Khz of I2C interface limitation.

But the hardest part is that keeping the constant switch frequency with reliable width-modulation because real time kernel might have over 2msec tolerance in the real world.
On that note, a change of plans then haha. I am going to use a arduino "beetle" as opposed to the gpio board. It has pwm output in the range I need and i2c for communication. I have an extra one from a project I did (they are only $7 so I had bought extra). This should free up resources and be fun to do. Being a 5v board, is it ok to power it through the H2's 5v pin 2?
Image

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Re: splice 12v fan to pwm

Unread post by odroid » Tue Aug 20, 2019 3:52 pm

H2's 5V output must be enough to handle the small Arduino.
But its IO voltage level is 5V while H2's I2C ports are 3.3Volt.

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Re: splice 12v fan to pwm

Unread post by spitefulmonkey » Tue Aug 20, 2019 4:44 pm

odroid wrote:
Tue Aug 20, 2019 3:52 pm
H2's 5V output must be enough to handle the small Arduino.
But its IO voltage level is 5V while H2's I2C ports are 3.3Volt.
Correct, I will use a logic level converter. I have many of these sitting around here for this reason. 5v to 3.3v

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Re: splice 12v fan to pwm

Unread post by odroid » Tue Aug 20, 2019 5:00 pm

It looks okay.

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