Hello,

I've started to work on a new project, and Interested in finding a PIR that it's maximum sensing range is one cm. I've looked into:
http://www.mouser.com/ProductDetail...=sGAEpiMZZMvhQj7WZhFIAHvIigpfBeUiLlWU3xYnD5A=
In this one, I'm not sure how exactly it'll work because I'm trying to minimize the number of processes (since the project will run on battery).
http://www.mouser.com/ProductDetail...=sGAEpiMZZMvhQj7WZhFIAJpSmd2sL2VeekwkKHWNq70=
This one is a little pricey.
In either case, the range of these is far greater for what I need, do you have any recommendations for a very short range motion sensor (ideally, I need it to output high when it detects a movement to wake up the rest of the circuit).

Thanks in advance.

 

Maybe you just need a beam interrupt sensor; a narrow gap with a IR LED on one side and a detector on the other side.

 

Hi wayneh,

Isn't that essentially what the device in the first link I provided does?

 

I might make another board just to run a couple of these:
https://www.sparkfun.com/products/241

that will wake up the main board in case of a event.... Does that look reasonable?

 

There are PIR (Passive Infrared Detector) motion sensors, which typically have a range of several feet, and are built as a single unit to detect the IR from (typically) a warm-bodied animal. Then, there are IR emitter/detector pairs which are active devices and employ a beam break mode of operation; sometimes these can be used up to a few feet apart, but often they are used with the emitter and the detector very close together. Which function do you need?

 

hi tracecom, thanks for the comment.
Well, The goal is to sense a bug size object. I'm afraid that conventional motion sensors will be too noisy for this (since, as mentioned, they'll pick up random movements of people in the room), so I guess I've to opt out for a beam breaker although it's less energy efficient. Would you agree?

 

hi tracecom, thanks for the comment.
Well, The goal is to sense a bug size object. I'm afraid that conventional motion sensors will be too noisy for this (since, as mentioned, they'll pick up random movements of people in the room), so I guess I've to opt out for a beam breaker although it's less energy efficient. Would you agree?

Does this object give off heat? If not, then you are limited to something other than a PIR.

Does the object move in a defined area? If not, then a beam break system won't work. If it does move in a defined area and the area is small a beam break system will be easier than if the area is large. The cheapest option is a pair of ordinary LEDs facing each other and spaced rather close. When one is lit, the other will produce a small voltage, which can be used a a trigger for another circuit. The next step up would be an IR LED and a paired IR detector, which would work the same way, but with more precision. There is also the laser beam option. In order to get a good recommendation, you will need to provide more detailed information. Or, you can experiment; that's always fun.

 

Exp is fun, but time is important too
Yes, the object moves along determined narrow path (~1cm wide), so either PIR or beam breaker would work.
My main concern is low power, and it seems that beam breaker requires more energy while PIR will pick up noise b/c of the, relatively, "over" sensing (I couldn't find PIR that its max range less than 20cm, I need one with max range of ~1cm).

Lastly, how would 2 regular diodes help in object detection? Sure they can alternate if connected opposite, but I fail to see the sensing aspect.

Another option is piezoelectric (but I'll have to experiment with this option since bugs are very light):
http://www.karlssonrobotics.com/shop/piezo-vibration-sensor-large/?gclid=CInDuo6d_bQCFSmCQgodujQA9A

Thanks again for your thoughts.

 

My main concern is low power, and it seems that beam breaker requires more energy while PIR will pick up noise b/c of the, relatively, "over" sensing (I couldn't find PIR that its max range less than 20cm, I need one with max range of ~1cm).

PIR won't work unless the object gives off heat.

Lastly, how would 2 regular diodes help in object detection? Sure they can alternate if connected opposite, but I fail to see the sensing aspect.

It's not "regular" diodes; it's LEDs and I explained how they might work.

I am going to a movie now, so won't post anymore until later.

 

Isn't that essentially what the device in the first link I provided does?

Pretty much, but I was thinking of something like this instead of a reflected light path.

Since you're looking for a bug that is so close to the sensor, would capacitance work? I think it requires contact, but maybe it's an option. Or how about sound (or ultrasound)? A bug 1cm from my ear makes me crazy!

Old TV remotes used to use high frequency sound instead of modern day IR, and you can still find the microphones they used for detection. I can remember my neighbor's TV would change channels every time the dog - with its metal chain collar - ran by the TV.

 

Normal PIR doesn't match your need, PIR needs heat and big object.

You may use IR or LDR to do the job, if you want to increasing the sensitivity, you could use two LDRs and place near by, and use Op Amp as LM324 or comparator as LM339,LM393 to compare the value of two LDRs.

Whatever you use IR or LDR that they all can do the job, if you using LDR then you will need LED to be the light for LDR, and when the bug pass by then the LED light will be reduce more or interrupt, through the comparator can be detect the signal, and send out the High signal.

 

Thanks for the suggestion, I think I'll order a couple from both. Your suggestion certainly save me time in aligning the LED and the photodiode.
The problem is that the device should be passive as much as possible (b/c a bug might come by today or in a month from now), so it needs to be very energy efficient.
Having build an ultrasonic range finder, it's not that power saving....

I'm very tempted to try the piezoelectric pads I've posted in the previous message. Have you seen it? Although, idk if a bug can generate any voltage from it, I guess I have to go and catch some bugs .

Ideally, the sensor/trigger itself should use very little power....

 

Hi Scott,

Thanks for the suggestion. At the moment I'm leaning towards a simple IR emitter/receiver pair with a simple comparator circuit. Although, I hope the piezoelectric sensor will be sensitive enough, if it is I'll have a completely passive trigger.

 

What kinds of the bugs do you want to detect, and how about the size(long)?
Does the bugs will reflecting the light?
Because when you used the reflection type of IR, it needs the bug reflecting the light to the receiver, otherwise you have to use the IR face to face, and let the bugs pass by to interrupting the light.

 

yeah, a couple of parallel IR (face to face) and then it'll trigger the circuit every time it'll go to low. I'm not expecting a mass of bugs, just a couple, at most, at a time.

 

Thank you all for your comments, I've got on the right direction now.

 

Bugs like roaches are glossy dark brown, that is a really poor IR reflector. You will be better off with a IR beam-break.

 

What kinds of the bugs do you want to detect, and how about the size(long)?
Does the bugs will reflecting the light?
Because when you used the reflection type of IR, it needs the bug reflecting the light to the receiver, otherwise you have to use the IR face to face, and let the bugs pass by to interrupting the light.

Like this?

 

Like this?

Is that you joined the racing or just watched or pic up the photo from Internet?

Here is a video that it may interests you to thinking over.

The Cockroach Controlled Mobile Robot (Higher Resolution).
http://www.youtube.com/watch?v=kA87IctQ17U

 

Lol@the racing....

Actually, I've done some more reading about beam breakers and piezoelectric sensors, and I have another question but it'll be in a new thread.

Thank you all again.