Simple presence detector help?

[Kyle]

I'd looking for help designing a simple circuit. I've drawn up a flowchart of the logic below. The "PRESENCE" in the flowchart is meant to represents a person activating a sensor. Any help is appreciated. <p>START
|<------------------
| |
|<-------- |
| | |
| | NO |
\/ | |
PRESENCE---- |
DETECTED? |
| |
|YES |
| |
|<-------- |
| | |
| |YES |
\/ | |
PRESENCE---- |
DETECTED? |
| |
|NO |
| |
| |
| |
\/ |
RUN MOTOR-------------
FOR TIME PERIOD

[Chris Smith]

What kind of “presence” are you looking for?

After that, what kind of logic do you want to set off?

[2M MACHINING]

Would motion detecter work to sense presence?<p>That type of detecter is low cost,and should be easy
to interface with motor on circuit.

[Gorgon]

Hi Kyle,
Is this the flowchart?<p>Read presence -> yes -> wait for no presence -> yes -> start motor for period -> return<p>
For this you can use a normal IR motion detector, with one catch. If you need to be sure that there are no people present, you need to combine it with something else. A motion detector do what it say, detect motion (or temperature differences). If the person stand still, it will stop detecting presence, and your motor will start regardless of the present person.<p>It all depends on your application and the environment it is installed in. I think we need some more info on this to give you a more detailed advice. <p> <p>TOK<p>[ June 01, 2005: Message edited by: Gorgon ]</p>

[haklesup]

In essance it depends on what range and to what precision you want to detect presence.<p>Robotic equipment is often protected by a "light
curtain" this is basically an IR laser and detector and an array of mirrors. (It's a lot like the way alarms are depicted in movies like mission impossible) when the beam is broken presence in the protected zone is detected and the robot stops cold (but does not restart without user intervention).<p>PIR detectors can have a far range that may be too sensitive or too directional. They also are made to detect movement, so if the subject stood still too long, the sensor would forget he were there. They are cheap, real easy to find and easily adapted<p>Microwave alarm sensors sense movement within a volume and can see through some materials so line of sight and directionality are less of a problem but they still detect movement. These are also relatively inexpensive.<p>Ultrasonic can be set to detect movement or stationary targets but still requires line of sight and is highly directional and range limited. It's getting a little hard to find these modules but they were popular for auto focus cameras for a while.<p>IR (laser) Thermometer can be used to sense the temp at a specific spot. If it is at body temp (or higher than ambient) you have a person. this may be unreliable if the ambient temp is subject to wide swings or the people are heavily dressed. It is also the most directional and focused of the suggestions I have so the subject needs to be in a small detection zone.<p>Air movement or air pressure detector (various designs like "glass break detector") can be used to detect presence but can be easily fooled. they are best used when the protected area is a closed space like a room with a door or a car interior.<p>Oh, and lets not forget the simple pressure sensitive door mat.<p>I think a combination of microwave and ultrasonic would make a reliable detector that can spot stationary and moving targets indefinately. <p>It is very likly that you can adapt a car alarm system to meet your partcular needs as the sensitivities and activation times are often presettable on some alarms.<p>OK I answered how to detect presence somewhat but what about the logic of your flow chart: Simplified, you just want to run a motor for a preset time delay after someone leaves the area. Do you care if they return before the motor times out? (i.e. automatic bathroom washing circuit) <p> Simply put, you just need to activate a motor with delayed turn off whenever presence is not detected (start when not detected). Don't really need a flow chart unless you want to implement this digitally in a program of some sort where this would be a subroutine.<p>
Probably the easiest implementation would be an X10 EagleEye PIR sensor (setup with delayed turn off) and a X10 (RF) Appliance module to activate the motor (or relay). I believe these sensors can be programmed with delays after detection and for turn or off (if not you can invert the output with an SPST relay just power the coil with the module and connect the AC and load to the switch) A time delay relay would give you even more flexibility.<p>Sensor detects movement and turns on output for at least 1 minute (or instant) and continues to do so while movement continues. meanwhile the relay is closed and the load, connected to the NC side and is thus off. When movement is no longetr detected and 1 minute has passed the sensor turns off which de-energizes the relay which closes the NC switch side and activates the delay relay which runs the motor for the delay it is set for.<p>If you prefer a digital approach than use the sensor connected to PIC input and relay connected to PIC output with program inside recipe. with this method you can more easily deal with multiple sensors and their limitations or complex logic for deciding when to activate the motor

[Bernius1]

Hey ! Has anyone tried a cordless barcode scanner ? With every pass, all you'd have to do is store the data string, and compare it with the next/previous pass. And two might give depth of field .
Try this site for industrial light curtains and scanners.
Lots-o-downloads.

[Kyle]

Sorry for the delayed response! This is my first time posting a question to these forums and I just assumed that I would receive an email if anyone responded. <p>The "automatic bathroom washing circuit" is precisely the logic that I'm looking for (my ASCII design didnt come out that well..). Anyone have any links to that? I think that the sensor that in that device would work as well, is it a PIR? Thanks for the help guys, I really didnt expect such a response!