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Author Topic: Detecting human presence - LMI 878 IR detector  (Read 2909 times)
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I'm trying to detect the movement of people to simply see if someone's around, nothing fancy. Im using the LMI 878. I've got it wired: D to 5v via 10kohm resistor, S to an analog pin and ground to ground. I don't seem to get any usable response out of it unless I'm missing something. I suspect I need a special breakout board but I'm hoping not.

Regardless, I'm looking for an inexpensive, compact way to see if someone walks in front of my project. Preferably even if they are far away(across a large household room), and also preferably not set it off with a fan or something else moving. It's for the front of a clock so I hope for it to not look too awful. If I can do it with just this thing then that would be great, otherwise I would really appreciate some suggestions.

Thanks very much.
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maybe you better try on of the SHARP distance sensors. These have different ranges and if someone passes the device the distance is changed so you can react - you can even give different reaction depending on the distance (e.g. the pitch or volume of a sound)
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Rob Tillaart

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That looks pretty good. The only problem is that the one that does the range I need is pretty big for my project. Also I'm wondering what the angle is, it seems like it just measures what's directly ahead because there's no mention of angle range. I was hoping for more like 90 degrees or more. I'll keep looking into them but I think these might not quite do it. Thank you though.

Also on second glance I realized the furthest range I could find was 5 feet which it much less than what will do for this project.
« Last Edit: June 25, 2011, 04:20:35 am by stoopkid » Logged

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Does anyone know about the LMI878? Should I be able to use it alone or is it useless without some kind of breakout board?
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Also on second glance I realized the furthest range I could find was 5 feet which it much less than what will do for this project.
Can you more specificly specify the requirements in terms of angle and distance [range]
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Im using the LMI 878. I've got it wired

The link under the LMI 878 point to a datasheet of an LHI 878 ; could be similar or not. At least I could not find a ref to LMI 878. The site under the pdf referenced has at leas no info about the LMI 878.

Rob
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Yes I'm sorry, LHI878, I must've typo'd at some point and I've just been referencing it since. Any info on how to use this thing would be great but I'm about 90% sure it depends on additional hardware.

As for my range, like I said, I'm looking for movement in a room so 15 feet at least would be nice but I suppose as little as 10 could do. On the low end, as long as it could respond to movement two or three feet away that would do, closer than that wouldn't really be necessary. And for the angle, as much as possible would be preferred but as little as 45 degrees would be acceptable.

I don't need anything fancy. I don't even need to be constantly monitoring movement. I just need to wake up my clock with motion detection and have it turn off 10 or 20 minutes later unless it detects more movement and continues to wait for that amount of time after the last motion is detected.

I was looking at this:
http://www.newark.com/jsp/search/productdetail.jsp?sku=14T0562
However I am worried about the response time being 30s. If that means that I can only take a reading every 30 seconds that's fine. But if it means it takes 30s to report movement, that's no good for me. I'm hoping for the clock to wake up relatively quickly after it senses motion, like a few seconds at most. Also I wanted to be sure it has everything included to be usable with the arduino unlike as I suspect the LHI 878 does not.
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How big is your project?  I.e. what are your size constraints?

I've made a similar project for Halloween using an ultrasonic sensor (A Parallax PING, but there are cheaper alternatives) and that allows for very fine distance of upto 10 metres in 1cm increments.

For the Parallax you're looking at $30~, for the MAxbotix stuff might be better for you as you can choose your required beam angle.  I use Cool Components (http://www.coolcomponents.co.uk/catalog/index.php?cPath=36_60) in the UK.

Regards,
Morrolan
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The enclosure will be about 4x8x4 but most of that space will be occupied by components. So I was hoping for something as small as possible. I don't really know the exact dimensions I will have space for because I can't really move ahead until I figure out what I'm using.

Do the ultrasonic ones make audible noise? My experience with them has made them seem pretty noisy with clicks.

I think I'm gone try that component I linked above however I've still got those questions about it.
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Unless you have incredible hearing you shouldn't be able to hear the ultrasonic sensor at all - after all, ultra-sonic does suggest it is beyond normal hearing smiley-grin
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Do the ultrasonic ones make audible noise? My experience with them has made them seem pretty noisy with clicks.

Unless you're batman you cannot hear ultra sonic directly, what could be that you hear something clicking that reacts on the ultrasounds, sort of interference. Can be part of the device that is not connected/mounted well or so. 


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Presence sensing is one of those things that is easy to do badly smiley-razz  Honestly, I have yet to run into a system that does not generate false reports (either positive or negative).  I've found two technologies to be very useful in this area: passive infrared and doppler/x-band radar.  The Sharp distance sensors are very nice and easy to work with, but this is really not the problem that they are meant to solve (they are really for detecting presence/movement in the 0 - 14" range, give or take) .  Ditto for ultrasonic sensors.  Yes, you *can* achieve a limited sort of motion/presence sensing with these technologies, but IMHO they are the wrong tools for the job given the requirements that you've stated.

Parallax makes a nice radar sensor that is great for a 8' - 30' range: http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/x-band/List/0/SortField/4/ProductID/606/Default.aspx; I've also had decent luck with cheaper models purchased via EBay: http://www.ebay.com/itm/130512020245?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_3211wt_1114

Check out the Zilog Z-pir sensors as well - about $6.50 from mouser http://www.mouser.com/ProductDetail/ZiLOG/ZEPIR0AAS02MODG/?qs=sGAEpiMZZMv2WiXdFcmpiDB8nPmOn4Po.  These are microprocessor based, low power, and painfully simple to integrate with arduino or other uC projects.  They support direction sensing as well (did the person move from left to right or the other way around?) which is fairly accurate.

The ping sensors are actually quite nice.  Just don't put them in a metal enclosure unless you fancy a migraine (my old ears are still sensitive to high frequencies, so I may be an outlier in this case).
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I ended up getting a panasonic pir sensor that has everything integrated into the tiny lens package. It works perfectly but im a little bummed they are $10 each. I was going to look into building it myself with just the sensor, lens, and try to make or buy the board myself for cheaper but I don't know how much that would save me in the long run. I might just deal with the price tag for this massive amount of convinience.
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