If I only had a Brain!

[Mikey p]

Do you mean the projector light will turn off but the fans will stay running to cool it down?

[tjh]

Originally posted by Luca Brazzi
Ive GOT IT!!!!

Thanks folks!!!

What Im going to do is design the controller to use a motion detector as the "Reset" for the projector staying on! If there is no motion in the room for 2 hours... the projector will turn off.

Of course Ill use a Pet Sensitive Alarm system motion detector... I wouldnt want the pooch walking around when Im not here to keep the projector running...

Sounds like a great idea, and I like all the other ones, but what happens when your watching a movie or something? wouldn't that be detected as motion?

[Luca Brazzi]

Sounds like a great idea, and I like all the other ones, but what happens when your watching a movie or something? wouldn't that be detected as motion?

I dont know... I know that motion sensors are triggered by infrared I dont know if the PJ would produce enough infrared light to trigger one though... Ill have to do a test.

Why not just get that Honda robot to tend to the projector while you're at it? Or, you could try B-4, Data's (from Star Trek) surviving brother. He's kinda stupid, but I think he could handle it!

Dont you think that would eat into the money I save by building a DIY projector?

[Luca Brazzi]

Sounds like a great idea, and I like all the other ones, but what happens when your watching a movie or something? wouldn't that be detected as motion?

Ok... did a test...

I ripped the Motion Detector off of my Alarm System, and powered it using a 12v wall adapter. Even putting the detector right in the light path in front of the projector 2" from the projection lens didnt trigger it. Keep in mind though... I have an IR mirror inside the PJ, and Im only using a 250 watt bulb.

Maybe someone else with a different configuration has had an experience where their projector set off a motion detector?

I doubt that there would be enough concentrated IR in a projected image to look like a human beings IR body signature though...

[mbates14]

comment about the fans:

Most high power output fans, like in commercial projectors have a third yellow connection.
the Sense wire.

So if the fan isnt running, the CPU will see no RPM reading from the sensor, so guess what, you can have an errorhandler built in the pic that says, Hey, im not reporting anything from the fan. So, go into shut down, and print an error code on the LCD.

Its not hard.

When i say LCD, I mean one of those little 2x20 or 2x16 8-bit joggers.

[Luca Brazzi]

Most high power output fans, like in commercial projectors have a third yellow connection.
the Sense wire.

Good thought...

For those of us... like me... though who are using plain old computer fans... there is no sense wire, just the black and red, so either I:

A) Sense airflow in front/behind the fan

B) Sense Votage/Current running through the line... ex: Fan off=0 volts, Fan running=12 volts, Fan powered but not running=? (I guess the answer would be something other than 0 or a steady 12 volts)

I think the most reliable way is to detect whether there is airflow through the fan (fan is actually spinning), but that would probably be the most hardest to sense.

Another thing that could be done would be to place an IR detector/emitter pair on either side of the fan... then the controller could detect whether the fan was spinning/not spinning easily by detecting whether the IR signal being picked up by the detector was fluctuating. A rotating fan with this setup should output a fluctuating voltage from the detector as the fan blades interrupt/allow the IR light to pass through to the detector. A NON rotating fan would output a steady voltage from the detector.... either always ON... or always OFF depending upon whether the fan is stuck with a blade blocking, or allowing the IR light from the emitter to pass.

The question is...

Can an IR detector distiguish between the IR emitted by the emitter on the other side of the fan, and the IR generated from the lamp?

Time for another Test!

[mbates14]

well, it would be a rather complicated circuit, but with those type of fans, youll most likely pull a tad more if the rotor is locked.

aka "locked rotor current", even though it is NOT AS MUCH as a standard motor, but a brushless motor drivin by a steper ocillator, it will "still" draw more current, as since the magnet rotor is not turning, its a heavier load on the drivers.

so, lets say hypothetically, if the fan is running at 12ma. well, you can make a circuit that knows the fan runs around 11 to 13 ma.

well, when the rotor is locked "ammeter to find this". it might pull a couple more miliamps.

lets say if it runs regularly at 12ma, if you stop the blades, it might start pulling 15ma (to get it started again).

if one of the drivers shorts, or opens, itll start bobbin back and forth, and it will draw less current (one of the drivers isnt there to pull the current).

Fans fail in one of the two conditions. If the oscillator dies, and it might not pull hardly anything. you can definatly see that.

You would have to build a current sensing circuit somehow.

[mbates14]

well, if you use IR, remember now, you still need a monostable circuit, or some kind of uPC. because when the fan runs, if you think about it, its a modulated light. (like a roller ball mouse, or optical mouse).

and the frequency of the light going on and off as the blades pass by can be monitored with a controller. if its steady, or dead, itll kill the relay, and disable the ballast, and maybe a warning LED might go on, hell, you can make whatever you want happen. I love that!!

but hey, you may be on to something there. the faster the fan runs, the faster the light will pulse on and off, and the higher the frequency. You can program a microcontroller, or you may be able to get away with using standard logic gates, and monostable "one shot" oscillators. and when the frequency gets past a threshold, (slowing down fan), you can have a gate toggle a relay to kill the bulb, and light a warning light.

[CCMCornell]

Lucca,

There are definitely 12Vdc computer fans with RPM signal. For computers, I have been a fan...err...of the quiet, inexpensive and reliably undervoltable Panasonic Panaflo L1A's which *don't* have RPM sensor, but I know a lot of Quiet PC enthusiasts who spend more on fans that do have them. I've also seen some lesser expensive fans with RPM monitoring but of unknown quiet-potential. I'll scrounge around to find some recommendations, but try out http://www.silentpcreview.com

Also, there are computer fans with thermistor control, so they can run after a certain temperature is reached. That may be an option.

[Dazzzla]

Just monitor the heat comming from the fan with a thermister.

DJ