If I only had a Brain!

[superdaveumo]

Another option might be to use a photoresistor. Place the photoresistor on one side of the fan and a focused light source on the other (a laser pointer perhaps?). The resistor would be MUCH easier to work with than the IR. My only concern would be if the photoresistor could change resistances that quickly... Hmmmmm...

Perhaps a prewired IR switch. Can't be that expensive. IR is a pain in the butt.

[cbm5]

It would be a hell of a lot cheaper to JUST USE FANS WITH SENSE WIRES.

Or go to the root of the problem: you don't want overheating? Use temperature and forget about the fans. I should already have a few Dallas or Maxim samples lying around, 1-wire interface thermometers etc.

[pinkmouse]

AD do a fan fail chip, can't remember the P/N, but it just monitors the negative/earth lead for fault conditions. IIRC, quite cheap as well.

[Guy Grotke]

I agree with cbm5: It doesn't much help you to know your fan is spinning, if your LCD is still running too hot. Rather than bother with fan RPM sensing, just implement 3 or 4 temperature sensors. The 1-wire sensors are very cheap & easy to use with a microcontroller. Using a bus interface would mean that people could add the right number of sensors for their projector design.

Then give it some PWM outputs for driving MOSFETS that can control 2 or 3 12 VDC fans. If a temp gets too high, it would be able to increase the fan speed. If that fails to cut the temperature, then you get a shutdown & alarm.

There are some nice optoisolated solid state "relays" (really triacs) that you would use to control power to the lamp circuit.

If you do want to use PWM to control a DC fan, then it is a lot easier with a microcontroller that has hardware PWM generation. Doing it well in software can be a pain, if you are trying to do other stuff as well.

[Luca Brazzi]

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

The thing I like about measuring a light source (IR/etc) is that it can be used for 2 purposes... First it can be used to determine if the fan is moving/stuck... and it can be used as the input to the fan speed control logic (frequency of the pulses from the detector=fan speed).

From what Ive read around here... and what Ive noticed on my own 4 fan projector, it would be beneficial to lower the speed of the fans as low as possible to reduce noise.

I agree with cbm5: It doesn't much help you to know your fan is spinning, if your LCD is still running too hot. Rather than bother with fan RPM sensing, just implement 3 or 4 temperature sensors

True... the ultimate goal is to protect the LCD from overheating, so yes temp sensing is definitely important. The fan speed sensing thing would be mainly for alarming you that there is a problem with your projector... Ive seen many PJ designs where folks completely embed fans inside the PJ where they cant be seen. Even on my PJ... where the fans are visible from the outside... Id like to be alerted in some way if one of them stopped spinning/never started spinning/etc even if it doesnt result in my PJ going into a meltdown situation.

IMO a fan problem could be treated 1 of 2 ways by the controller... A) Cause the PJ to shut down... or B) Cause a warning alarm to go off to alert you that there is a problem but not cause the PJ to shut down, and.... it could be different from fan to fan in the same PJ design... So what Im thinking is that how each fan is handled by the controller should be selectable for each fan. For example... in my PJ I have 3 fans blowing in, and 1 fan sucking air out... I would want to be able to tell the controller (if one of the 3 input fans stops working... no problem just warn me... but if the exhaust fan stops working, shut down the PJ)

If you do want to use PWM to control a DC fan, then it is a lot easier with a microcontroller that has hardware PWM generation. Doing it well in software can be a pain, if you are trying to do other stuff as well.

Either that, or there would need to be external circuitry to do the PWM.... Basically I would just want the Main controller to tell the external PWM circuitry/controller what the current setting should be for that device, then leave the actual PWM signal generation to the external controller.

[PaladinWOL]

I need help.

[Luca Brazzi]

Or go to the root of the problem: you don't want overheating? Use temperature and forget about the fans.

Yes... as I stated in my previous post Temperature is the ultimate criteria, however, I would still like to know if my fans are running or not, even if it only generates a "Warning" condition, and doesnt cause a complete system shutdown

[Luca Brazzi]

Ive got another question for the board...

If you had the option for an "Auto Shutdown after a Timeout" mechanism for your projector that was reset by "Human Motion in your Theatre", would you rather have the timeout fixed, or programmable?

For example would a 3 hour timeout with no motion be fine or... would you rather have the ability to adjust it to 2 or 4 hours or whatever you wanted it to be? I think that the shorter the time limit with no motion the better, but I also dont want to have to constantly be waving my arm/etc to keep my projector running

[cbm5]

Use Dallas real-time clock module and have the projector shut down automatically as a certain time every night...why not have it turn on automatically 10 minutes before you get home so the MH bulb is all warmed up?

[Luca Brazzi]

Originally posted by cbm5
Use Dallas real-time clock module and have the projector shut down automatically as a certain time every night...why not have it turn on automatically 10 minutes before you get home so the MH bulb is all warmed up?

Good suggestions.

I think what I will do is this...

In Version 1 I want some basic functionality

That being...

Shut the PJ off if there is no motion in the room after 3 hours.

What I want it to do is alert me via a low volume Buzzer 10 minutes before the timeout expires.

If I dont reset the timer (by moving) the PJ will shut down.

The circuitry should be simple.... a PIC Micro Controller, a Motion detector, a Buzzer, a Relay, and a switch

The problem is that in order to do this, the PIC needs to be the power control for the system...so I need to put the PIC inline on the AC power control (thats what the Relay is for) So... instead of me flipping an AC power switch to turn on the PJ I will push a button connected to the PIC and the PIC will energize the relay and turn on the AC power.

BTW... Ive come up with a name for this whole project... I call it the "P-Brain"

Ive setup a development Environment to build it... starting with the original function (shutdown the PJ after 3 hours if there is no motion in the room)