PIR sensitivity

Wolfbrother

Hi all, I'm doing a new sculpture where I want to focus the looking angle of the PIR sensor. I have tried using a PVC cap like on Scary Terry's site but it really doesn't seem to do much. I am seeing a good amount of false positives and I'm not sure what the best method for reducing the sensitivity is. I tried to implement a simple debounce, see attached code, but it still sees a large amount of false positives. Basically the premise is the PIR sensor sees you in front of these things, the motors then actuate for a period of time and then the whole thing calms back down waiting until you approach it again. Any ideas on the sensitivity issue? Should I maybe just use a photoresistor like they do in the halloween props? Any suggestions would be great.

Thanks,

Dave

Franklin

What kind of responses and distances are you getting? Are you waiting for the PIR to settle down after powering? Could you post your circuit so we could take a look?

Wolfbrother

I have no idea what distances the false positives are at. They just keep occuring. As far as real positives they occur anywhere from directly in front of the sensor to more than a few feet. That part seems to be correct, it's just these false positives. I have even pointed it a large sheet of plywood in the hopes that the plywood would be homogeneous temperature. Still random ones. I tried replacing the PIR as well, since I haven't seen this issue so much before. I don't have a wait built in to my software, but I do wait some time for the PIR to settle and it still randomly sees things and triggers.

The circuit is simple. I'm using the BOE. Servos on pins 12, 13, 14 & 15 through the servo header. Pin 0 directly to PIR signal, Vdd and Vss going where they are supposed to. Nothing else. I can draw it and post it, but there isn't much happening there.

Any ideas?

Franklin

Add a pullup/pulldown resistor to the sigmal pin to whichever rail is the not detected voltage.

ElectricAye

Is this a Parallax PIR? I made a bear detector using some non-Parallax PIRs and if I didn't put a 10K resistor between the PIR's data out line and the ground, I swear the durn thing could see my hand through a sheet of cardboard. I guess that without the 10K resistor, charges would build up on the data line and just stay there or, once a real motion was detected, the charges just stayed there and kept setting off the alarm. The 10K resistor helped bleed away the charges from the data line. I'm not sure the Parallax PIR is set up the same way, but such a resistor between your Pin 0 and ground might be worth a try. If you don't have a 10K, something like a 50K or 100K might work, too.

Wolfbrother

Hi all,

I tried the pulldown already, I think that's a great suggestion and certainly made sense to me. It didn't stop the false positives at all. Here's what it looks like is the problem. I live in Southern California and my little work area is a converted one car garage. I have a fan to cool it, but cooling is a relative term. This morning my room was a pleasant 67 degrees. The circuit works perfectly. Yesterday afternoon it's easily 85 in here, maybe a bit more. I'm guessing the sensor was saturated with heat. I'm thinking these things might be more or less set to look for people in a room and when you get a room that's about the same temp as the people it's looking for, well... it thinks it must be people too.

Thanks for the good thoughts.

Dave

ElectricAye

Wolfbrother wrote: »

Hi all,

...I have a fan to cool it....

Have you tried testing your PIR without the fan running? PIRs look for changes to the signal. I know my bear detector wouldn't work if part of it's field of view included a lake - it turned out the reflections from the rippling of the water made the PIRs think the thermal field was changing, so it kept sounding an alarm. Is it possible that the rotating fan blades are interrupting a light/heat source and/or reflecting heat from someplace and faking out your PIR?

Wolfbrother

When I put the unit facing the plywood board, I did have to turn off the fan, since the fan was in the way of the front door. This morning when it was cool, I also had the fan running so I can cool the room as much as possible before the sun makes it hot.

It seems that these units are pretty sensitive, I would like a way to numb it a bit. I have it mounted in a little tube, in the hopes that would focus it. That more or less seems to work. Maybe there's a different lens combination I could put on it to diffuse the outside signal coming in. I'm also looking at other motion sensors that are available. I'm really liking the MA motion sensors.

Thanks,

Dave

ElectricAye

I've attached a couple things you might find helpful. The PIRs I used for my bear detector were more sensitive than those at Parallax, but they also cost a lot more.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=255-1803-nd&x=18&y=12

Wolfbrother

Hi,

Thanks for the links. I'm thinking about ordering one of the x-band motion detectors since it says it's more immune to false triggers.

bstewart63

You can try putting something over the lens to knock down the sensitivity.

I was using mine outside and kept getting false triggers from wind and such. I had some red lens tape from the auto parts. I put this over the dome and it helped a lot.

Jumanji

I am also having the same issues with the PIR sensor giving false signals. I am powering it from 5V and have it inside a cardboard tube to limit its field of view and I have a 100K pulldown on the signal out pin. It is connected to an Arduoino Uno with about 6" wire. It is sitting in a room facing a wall and it gives a false trigger about every 10 minutes. Yesterday I had it outside and it was completely worthless - it went off almost continously.

ElectricAye

Jumanji wrote: »

I am also having the same issues with the PIR sensor giving false signals. I am powering it from 5V and have it inside a cardboard tube to limit its field of view and I have a 100K pulldown on the signal out pin. It is connected to an Arduoino Uno with about 6" wire....

I don't know anything about Arduinos but do you have any resistors that will limit current from the PIR to the Arduino? With the Propeller, I found that I needed not only a pull down resistor but also a current limiting resistor of about 2K as well.

Also, you might try a smaller resistor for the pull down, maybe 10K instead of 100K.

Remember: the wall might be very reflective in IR, so if you or anything else is moving around behind the PIR and changing the IR signals in the room, the PIR just might be picking these up.

T Chap

I tried using the Parallax PIR for motion sensor but got pretty frustrated trying to get it solid. Every time the AC kicks on in the room, it triggers. I have read that all PIR sensors are affected by temp. As an alternative, the PING does a nice job of sensing motion or objects within a distance, and allows the option with coding to filter out objects outside a certain distance.

For PIR, I recently starting using another manufacturers motion sensor and found it to be rock solid for use in real world motion sensing applications where false triggers would not be acceptable. You can find them from around $50 and up at many online suppliers. It does have a relay contact closure, but I just removed a resister and tapped into the 5V logic that triggers the relay for an output.

Bosch DS150i

http://products.boschsecurity.us/en/TAMS/products/bxp/SKUPFT3651023883.P1.4.998.800.236-CATMdc38e64c2b5e5dd4f70951f2f030d4bf