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Need Help Building A Fan Controller

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Frosty_47

New Member
Hello to every 1 that actualy bothered to read this msg.

I am a NOOB at electronic circuit building. The only project I ever accomplished was building a simple fan controller using a few rheostats and LED's. I have no experience with CHIPS. I heard quite a bit of information about the LM3914 CHIP, and now I want to build a fan controller for my computer using the old rheostats and this MAGIC CHIP. I want to use a 10 segment LED block but I have no idea how to hook it up. The input Voltage to the rheostat is 12V. The output voltage obviously going to vary depending on the position of the shaft of the rheostat and the load. I just want to build a small circuit that will light up more LED's as the voltage goes up and will extinguish LED's as the voltage drops when I turn the shaft on the rheostat. As I mentioned earlier, I do not have much experience and I don't know were to look for answers except this place that looks very attractive to me :D.

Any suggestions would be appreciated with great prosperity regardless of their nature.

Thanks,


Andrew (Just another noob entering the highly sophisticated world of electronics)
 
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audioguru

Well-Known Member
Most Helpful Member
The datasheet for the LM3914 and for all other ICs shows how to use them and has example circuits.
 

stevez

Active Member
You mention two things that you want to do:
1. Build a fan controller for your computer.
2. Build a voltage indicator.

I'd suggest doing #2 first as a warmup project. Keep in mind that it might or might not be useful if you progress to #1.

Regarding the fan controller I have a couple of comments:
A. Your rheostat (variable resistor) will lower the voltage going to the fan (or other load) by dissapating the excess power as heat. If the current requirements of the motor (or other load) exceed the ability of the rheostat to handle it you will ruin it and the motor will stop.

B. If the fan runs all of the time now and you add some means of adjusting the speed you may risk damage to your computer. One would have to ask how you'll know when to increase the speed - and if it's manually, are you going to be there when it starts to warm up.

C. There are numerous projects out there where people have added a means of controlling the fan speed. By controlling I mean just that - not just reducing the speed. They have some indication of load (usually temperature) and they electronically adjust the effective voltage to the motor so that the fan only runs fast enough to get the job done. I presume this is done to reduce noise. They often use Pulse Width Modulation (PWM) control. The motor sees pulses but handles them as if they were a reduced voltage. A voltage indicator (your #2) may not behave predictably with PWM.

These might be good projects to start with however I'd encourage you to just get an old computer fan and use that. Don't fool with your computer just yet. Make a mistake, which is likely, and you may ruin the computer.
 

Frosty_47

New Member
Need Links to tutorials...

Thank you for taking time to read and reply to my question regarding the fan controller. As I mentioned earlier, I already build a fan controller using rheostats for my computer, and it's been running my fans for more than 6 month now without any problems. The power consumption of my fans does not exceed 3 Watts per fan. Each fan is attached to a dedicated rheostat that is ratted at 15 Watts so this project is relatively safe. Besides, I have a good Power Supply (Antec Safe Power 450Watts with overload, temperature, short circuit, over voltage and over current protections). I appreciate your suggestion regarding temperature controlled fans, but this is not what I want to do at this time. I am interested in building a fan controller with a voltage indicator. My obstacle at this time is the lack of information about the LM3914 CHIP. I looked at the technical data of the LM3914 and I still did not obtain enough information about the chip such as information regarding Voltage and Current Limitation through-out particular pins of the chip. The example circuits provided in the technical data are not fully explained (ex. Why is there a 3.3K Ohm resistor attached to Pins 4 through 6?? [No explanation what’s so ever]). The technical data sheet of the LM3914 CHIP probably contains enough information for an expert, but not for an average Joe who is looking at it for the first time.

Does any one know of any good links where information regarding the LM3914 CHIP can be understood by NOOBS and not just Experts and Pro’s? Or links to a tutorial for a voltage regulator?


Thanks,


Andrew
 

audioguru

Well-Known Member
Most Helpful Member
The LM3914 is simple to use and its datasheet explains it very well.

With just a single resistor to set LED brightness, its full scale input voltage is 1.25V. With another resistor added then its full scale input voltage can be any reasonable voltage you want.
 

musthave

New Member

Frosty_47

New Member
rrrrr.....

Hokay,

I checked the datasheet of the LM3914 one more time...It will be the last time I look at it because the datasheet is badly explained as to more precise indications for the pins. Can some one please explain the pins on LM3914? I only know that PINS 6-7 control the current to the LED's (At least now I know how to make them brighter :D).

Thanks....
 

audioguru

Well-Known Member
Most Helpful Member
The LM3914 is simple.
You are a NOOB and you won't understand my geek-talk about it. Sorry.
 

Frosty_47

New Member
Bout To Go P0$t4l...

WOW Uncle Scrooge !

Do you like live on this forum ? Like how do I know ur a person and not some crazy high tech software made by Electro-Gods...A software that automatically responds to all the posts in a very small amount of time... just messing with you.. ;)

Yes you are right about me being a big time NUB at electronics... But weren't we all at some point in time ? Anyways, all I am asking is the explanation of the PINS of LM3914. For example... "The size of the resistor on pin 6 going to ground determines the current of each LED ( V/R1=#mA)" I can clearly understand that !! I just don't know any info regarding the other PINS and the tech-data sheet is MESSED -UP big time!

Thanks for ur time...
 
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audioguru

Well-Known Member
Most Helpful Member
Frosty_47 said:
"The size of the resistor on pin 6 going to ground determines the current of each LED ( V/R1=#mA)"
No. The LED currents are 10 times the current from pin 7 to ground. You must calculate the value of a resistor to pin 8 then another resistor from pin 8 to ground to provide the current and to set the pin 7 voltage.

I just don't know any info regarding the other PINS and the tech-data sheet is MESSED -UP big time!
It isn't messed up.
Pin 2 is ground and pin 3 is the positive supply.
Pin 5 is the input
Pin 4 and pin 6 are the resistor ladder for the comparators.
Pins 7 and 8 are an adjustable voltage reference.
Pin 9 is the Mode setting pin.
The remaining pins are for the LEDs.
Easy!:D
 

Frosty_47

New Member
Alright...

OK TY Uncle Scrooge !

Now that I know a little more bout the PINS ON LM3914; I can certainly start this project tomorrow using the article below. This article is exactly what I am interested in making...


**broken link removed**



I have only three more questions..

Why is there a 1.2K Resistor going to PIN #7 ?

Why is there a 5.6K Resistor going to PIN # 5?

Why are there a 5.6k + 680 Ohm Resistors going to PIN #2 ?


Everything else is Loud & Clear thanks to Uncle Scroodge, my friend Ugeen, and the author of this article... :)

**broken link removed**
 

audioguru

Well-Known Member
Most Helpful Member
Frosty_47 said:
Why is there a 1.2K Resistor going to PIN #7 ?
Pin 8 is grounded so pin 7 has 1.25V. Then the 1.2k resistor has 1mA in it and sets the LED currents to 10mA.
Pin 6 also has 1.25V which is the pin 5 voltage that lights the 10th LED.
Pin 4 is grounded so the 1st LED lights when pin 5 is 0.125V.

Why is there a 5.6K Resistor going to PIN # 5?

Why are there a 5.6k + 680 Ohm Resistors going to PIN #2 ?
They form a voltage divider so the pin 5 voltage is 1.25V and the 10th LED lights when the fan voltage is 11.5V. The 1st LED lights when the fan's voltage is 1.15V.

Everything else is Loud & Clear
I am glad you found that project which is exactly what you need.
 

Frosty_47

New Member
Weeeeeeeeeeeeeeeeeeeeeeee

Thanks for your help !

I am already in the making process of this project.
I will let you know if it worked as soon as I finish it.

Again thank you for your help…
 
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