Ok, by this point most of us know that computer fans run off the 12V line, and that if you unplug the respective ground and plug the 5V line in it's place, the fans can only draw at 7V. Effectively, a switch that can switch the 5V and Ground line becomes a fan speed controller to cut fans to 7 Volts. Now, some of you were aware of my "computer driven remote-controlled car" thread in which i used some basic electrical compontents [resistors, transistors, switching diodes, and relays] to close a circuit found in my RC Car's controller with a signal sent from the parallel port. Well, when I ordered the relays I ordered 6 [both times] in case something happened to any of them. That means I have 2 normally open relays and 6 normally closed [unwanted for the RC Project] relays remaining, which brings us here. Basically, I want to build two nearly identical circuits, seen below, to switch between 12 and 7 volts for my row of fans [I have 6]. The reason for this is that having 6 LED case fans produces noise and light that is unwanted for a dorm room at night. So, I'm using knowledge gained from this guide[the guide I used for my RC Car] on DAK Engineering's website to produce the circuit now seen below Both circuits draw power from the 5V molex line and receive signals from the parallel port to switch on and off. Basically, I would set the second circuit, which cuts the ground line [thus stopping the fans] to turn on at 11pm, and have the first circuit turn on 1 or 2 seconds later, changing the voltage from 12 to 7 volts, and decreasing the sound and light level of my fans. I do not have programming experience and expect I will have to learn a bit to write my own program, but mainly I need input regarding the integrity of the circuit and the design. Gracia -Andrew
why loose a parallel port for that may as well raid an old alarm clock, some sort of time clock to do it, its easier and doesnt use system resources. personallyy if i wanted computer control i would use the USB velleman kit (awsome for £25)
And you can do it with a single change-over switch (SPDT or SPCO) relay, common to fan negative and the other 2 contacts (NC & NO) to 0V and 5V. Hang on to your spare relays, they'll come in.
cpemma: i think i'll probably try and pick up a SPDT relay, that's a much better idea. do those, however, require constant current, or can the computer throw a pulse to switch it and then leave it alone? i'm by no means schooled on relays. i was thinking about how the computer throws out "random" signals through the parallel port on boot [not necessarily random, but practically, may as well be] and it would be very bad if both circuits were closed [first getting signal, second not] because the 5volts would go straight to ground [i believe] i'll see if i can pick one of those up by the way, if anyone has experience programming with the parallel port in windows xp, i could really use a little help to get me started and understanding what commands do what. i've looked at guides but don't have the greatest familiarity with the concept after seeing them. as far as wasting my parallel port on this goes, the parallel port hardly has any commercial use these days [almost everything is USB] and i'm already using pins 2-5 for my RC Car. I only have to add this on pin 6 and i'm set [i'm thinking i should make a pass through connection for my rc car so they aren't wired together. what do you think?]
i think i'm going after this bad boy next time i head to radio shack http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=275-240# not a fan of their high prices, but it's cheaper this way than with $6 shipping for a $1 item. i'm gonna need a little clarification with how SPST, SPDT, DPST, and DPDT relays differ, because i don't really know [my assumption, though, is "SP" means there's a common pin whereas "DP" means you could have 2 unrelated circuits that you're switching between and "SP" is "on/off" where "DP" is "on-1/on-2." correct me if i'm wrong, please] how do i figure out the pinout on this guy?
Think I found something I´m not sure but this one looks like yours, check it out: http://www.electronic-kits-and-projects.com/ds/az_relay.pdf Good lock!!
All relays need constant current to stay on. You can make a DP type stay on by using the unused pole switch to bypass the 'on'-switch when the relay is turned on, but then you need some way to break the power circuit to turn it off. Handy for 2-button operation of things, using a momentary-on to start and a momentary-off to stop. Or you can use your transistor switch with a thyristor instead of the transistor, again you have to interrupt the relay supply to turn the thyristor off. Or use a flipflop, one pulse turns it on, a second pulse turns it off. This page shows switch options with a bit on relay switches here.
Why do you need to change the speed of the fans? If it is temperature why not try a picaxe and ds-temp sensor thingy (www.tech-supplies.co.uk) If you only want it some of the time, a switch could be used...
motherboards already record temperature information. i currently run motherboard monitor and samurize, so i think i can rig up a little program to do the switching itself. just last week my friend and i threw together a VB program to control the parallel port, which means adding a timer function or anything like it is nothing. interfacing with the temperature information might require a bit more finess, but should be doable. I already have a relay, but i haven't wired it up yet [you know what college does to a guy ] -agent
well, the program is all set up and the whole bit is now functioning I am not an electrical engineer and cannot verify that any of what i drew is correctly drawn. I do NOT know the correct way to denote a SPDT relay. the way I did it was for my understanding only. [I don't want anyone to think this is a Basically, the two pins the relay switched between were the red and black wires on a molex cable and the output was the black wire on the other half of the cable. the yellow [12V] line is constant the first image is my visual basic program which writes values to the parallel port. I've assigned up, left, right, down, and the timer function to have an integer [X1, X2...] which are added in a function "X=X1+X2..." and "X" is the decimal sent to the paraport dll [ http://www.paraport.net/documentation/index.html ] and then respective pins are turned on. for anyone trying to learn this stuff, a page i found very helpful was apparently yanked offline, but the cached page is here [ http://72.14.203.104/search?q=cache...leon.com/+&hl=en&lr=&client=firefox-a&strip=1 ] so when my program is open, the timer function checks the hour. if the hour is greater than 20 [8pm] or less than 8 [8am] it assigns a value to X5 [the value is 16 because it's the 5th data pin, D4, actual pin #6]. because it assigns that value, the equation changes and is written to the parallal port. the arrow keys control my RC Car and the program controls all of them at the same time. i hope that makes sense. i really don't feel up to proofreading at the momemt. maybe i'll change it later andrew
