CTR Monitor VGA switch interface?

[Kookie]

I'm looking for an Idea or better yet, a simple circuit to solve my problem here. I have a 17" monitor that I had to box-in in some furniture on a desktop. It gets very hot when the monitor is on. I have a nice little AC fan that I would like to mount back there, but I don't wont the fan on all the time. I only want it on when the computer brings the monitor out of sleep mode and then preferably a five minute timer for the fan to be on when the computer sends the monitor back into sleep mode. I know nothing about the DB 9 pinout of the computers VGA monitor output. I'm thinking though that it might be fairly easy to tap off that signal to switch on/off an AC circuit (i.e. the fan in my case). Would anyone have any ideas (circuits) on how this could be done? Does anything like this already exist for computer monitors? I know they make video switches for VCR's and the like that do this. Thanks for any help here.

[Kookie]

OOps: CRT I mean, Ack, Typing not my bag, lol.

[Kookie]

Oh man, Oops again: DB 15 for monitors, proof reading would be a good idea for me, ack.

[bodgy]

Probably not too helpful, but this months edition of an European electroniks (the K is there on purpose) magazine has exactly the circuit you want.<p>It is a bathroom fan extender in the project.<p>Other than that there are a number of ways you could implement this. Maxim have a temperature sensitive fan controller IC, then you only have the switch on monitor sensing to deal with.<p>This can be either by having a master/slave socket arrangement where the circuit senses the monitor switch on by monitoring a current drop on the monitor mains in (however these always use non isolated DC power supplies, so that would depend on your constructional and electronics experience), or if your computer is one of the older type that has a mains feed through for the monitor, then you could put your fan device in series between the 'puter and the monitor, or you could (low tech, boring) , just plug the fan device and the monitor into their own socket board and use the socket boards switch to turn both on at the same time.<p>colin

[Kookie]

Hey yeah, that didn't even occur to me, that the monitor draws more current when out of sleep mode. I wouldn't even have to fiddle with the computer's output. Good, this makes this project a bit more tangible. So, I would only have to come up with something that senses hi/low AC current draw to switch on/off. That seams simple enough. It could be a box that plugs into an AC socket that the monitor plugs into and the fan plugs into. <p>Ok, as far as my experience go, I can put together anything from a schematic, but as far as design goes, I fall a bit short. I could assume this project may involve a triac though. That sounds fun. LOL.<p>I looked at Maxims IC's and they seem to involve 12V fans. I didn't see anything for 120V AC fans (the fan I have is a good little 80mm x 40mm 14W 120V 60Hz ball bearing fan). Nice little slick IC's though. Looks like a nice source of stuff, I page-maked that. Thanks.<p>I thank you bodgy for your input. I have a better idea how it could be done. I will look for European electroniks, although it may be hard to find here in Detroit, Mi.

[Kookie]

I don't know, those IC's would be good for another project. It seems it would way over-complicate this with temp sensing and all that. I'd much rather go with a timer so the fan would be on for a few minutes after the monitor shut down just to remove some of the remaining heat, then let it cool convectionally like its supposed to, and especially since its not producing any heat after shut down. Thing is, putting the timer on is not necessary as well, and complicates it more, but it might be a bit more efficient that way. The other point is that this isn't very crucial cooling, I just want the monitor to last a bit longer in its new enclosed environment. Whatever, though, and I thank you for setting me straight that I could use those IC's.

[Kookie]

Hey guys, this seems to be exactly what I'm looking for: http://sound.westhost.com/project79.htm But how can I add a timer to this so that that relay (RL1) would stay on for a few minutes?

[Ron H]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by chessman:
Use a TIP140 or other power transistor on the output of the IC. Collector of the transistor goes to the +120VAC supply, emitter goes to the + terminal of the fan. The - terminal of the fan goes to the - AC terminal, and you now have a MAXIM fan controller IC giving you 120VAC output.<hr></blockquote><p>Chessman, pardon me if I misinterpreted your answer. I read it as saying that you can use a bipolar transistor as an AC switch. This won't work.<p>Ron

[Ron H]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by chessman:
*ahem* don't the Maxim temp ICs have PWM output? i've seen the same thing done before.<p>if it's not a PWM output and just a 12V DC out, then have a transistor drive a relay for the 120AC<hr></blockquote><p>I haven't looked into the Maxim part. What I was taking issue with is this statement:<p>"Collector of the transistor goes to the +120VAC supply, emitter goes to the + terminal of the fan."<p>This won't work. You can't switch AC directly with a transistor. You CAN switch a relay, as you suggest, which can then switch the AC.<p>Ron

[Chris Foley]

Hi. If you don't mind something of a low-tech solution, have you looked into bimetallic thermal snap switches? These automatically open and close at preset temperatures, and I'm sure there's one that will do the job for you. The fan will cycle while the monitor's on, but if you choose the thermal switch properly, it won't turn on at the lower "Energy Saver" monitor heat level. It also has hysteresis, which means that once it turns on, the temperature has to get significantly lower before it snaps off. Some are made to switch up to 20A at 240VAC. One manufacturer of these is Therm-O-Disk, and some of their products are available surplus at<p>http://www.hoffind.com/thermal.htm<p>Mount one on a piece of 1/8" or 3/16" aluminum at least five times the weight of the switch itself. You also could try mounting it to one of those chassis-type TO-3 heat sinks. Put the aluminum in proximity to the monitor heat source (e.g. directly over the top vent), hook up the line, a fuse, the switch and the fan in series, and you're good to go. <p>If you insist on a silicon solution, you could try looking at the old RCA CA3059 IC, which has everything you need to run this except a 10K 2W resistor, your thermistor, and a triac and RC snubber.<p>data sheet: http://www.onsemi.com/pub/Collateral/CA3059-D.PDF
appnote: http://www.intersil.com/data/an/an6182.pdf<p>Read the appnote anyway, for something of a primer on solid state switching of AC loads with triacs. The part is obsolete, I guess (sorry how that works -- it seems you just get to know them, and they fade away), but still available as Harris/Intersil and On Semi from many sources. Be careful, as always, with line voltage prototypes (don't do this unless you know what you're doing, don't work with line voltage alone, and always use an isolation transformer for build, test, debug).<p>Hope you've got what you need here. Happy hunting.<p>[ March 06, 2003: Message edited by: Chris Foley ]</p>