PIR Sensor Hacking - Page 1
Forum section: electronics / projects

author: SockThief
author_rank: Contributor
timestamp: August 08, 2012, 11:28:49 am
content: G'day Brains Trusthave a new project im thinking about getting around to doing! But Im stuck at the first hurdle, and a few google hits later, with no answer, its off here to see what you guys reckon.What I need to do is non-destructively hack a PIR sensor to constantly trigger as if motion is detected, without any motion taking place... the sensor is built into a weatherproof camera, hacking into the box to play with the sensor is out, as it will destroy the seal (as I live in Sweden - I need to ensure the best seal against the elements as possible), Im hoping that there is a simple solution to fool the sensor, maybe some al-foil over the sensor, but not sure at the moment.On the one hand, the sensor wants to detect as much motion as possible, in the sense of a security monitor, but not suffer too many false triggers. In my case, im thinking the camera is not too picky on the false positives, as the worst that will happen is some recording of a pet, so hopefully the tolerance is a little nicer, though I haven't bought the camera yet, as I don't want to spend the cash if it won't do the job, and so I'm not sure yet...any ideas?

author: Rerouter
author_rank: Super Contributor
timestamp: August 08, 2012, 11:32:08 am
content: high intensity IR led pointed at it flashing via a 555 timer, they scan for a change in the IR image rather than specific motion with most of the,,

author: SockThief
author_rank: Contributor
timestamp: August 08, 2012, 11:52:53 am
content: hrmm now that is an interesting thought.... the PIR sensor im looking at has a rather large FOV and sensing up to 15m, so an IR LED piggy backed on might just do the trickim mystefied at myself that I didn't think of that...!

author: SockThief
author_rank: Contributor
timestamp: August 08, 2012, 01:51:23 pm
content: With rerouters suggestion at hand, ive done some more googling, and it appears (at least in some models) that IR appearing and then disappearing wont trigger a PIR sensor, however an IR source moving would... could always bounce it off a rotating mirror!hrmm more thinking required...

author: muvideo
author_rank: Frequent Contributor
timestamp: August 08, 2012, 02:00:48 pm
content: Consider also that the IR range of interest for the PIR (5-15um) is far from the usualIR led range (0.8-1.1u). This could be a problem, you can also try a small incandescentbulb lamp instead of the led.Fabio.

author: SeanB
author_rank: Super Contributor
timestamp: August 08, 2012, 03:25:22 pm
content: 28V lamp in front of the sensor, driven by a 555 and flashing at 10 times a minute run off 12V, so that it barely glows. Will be detectable by the sensor easily.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 08, 2012, 05:35:31 pm
content: The problem could indeed be that the sensor needs a motion, so a detection that goes from one beam to another.Oh well, then you have to use 2 light bulbs some distance apart and a flip flop driving them...

author: SockThief
author_rank: Contributor
timestamp: August 09, 2012, 05:58:46 am
content: Leaving out vital parts of a project when asking for help, because you've been studying the issue for so long its all obvious to you! Now that, to quote Dave, is a trap for young players. Be warned children!Here is the critical missing info: sorry about that everyone!The camera I am considering is a Moultrie M-100. Its a small camera designed for hunting, so on the plus side its:- small- weatherproof- runs on 4/8 AA batteries with an excellent battery life (depending on settings - up to months)- standard SD Cards with standard JPEG output- time lapse functionality built in- reasonable resolution- 24 IR LED array for night visionBut as its primary function is for hunting, most functionality is triggered by the motion sensor, hence my issue here. There are other alternative cameras, for instance the Brinno TLC-200, which, again, is a small camera running on AA batteries with timelapse functionality, the downsides on this one is: the weatherproof box is not yet available, nor is the motion sensor, and the output of the camera is automatically saved as an 1280x1024 AVI file, whilst I can set the camera to 1 shot per second, and outputting at 1 FPS, meaning each frame is a single shot, Im still left with a 1280x1024 res image (as compared to the 8MP of the M100), which is likely suffering from compression artifacts from the AVI processing.In a nutshell, then, the key requirements on the camera side, is- long battery life, ideally the minimum battery life im striving for is minimum 1 month- standard AA batteries for ease of field replacement- constant time lapse and motion triggered- a *decent* resolution- weather proofSo all the suggestions so far, have been brilliant (and im still kicking myself that i didnt think of a moving IR LED!) though, Im stuck on how to make it a practical solution. For instance, if I were to be photographing the forrest around my summer house, and interested in the changes in the surrounds over winter, I would need a constant time lapse, and a moving lamp in front on the camera that could trigger a PIR sensor, would likely consume far too much power, and it, unfortunately would attract passers by in an unattended camera, and likely scare wildlife away, and also has the downside of requiring to be weather proofed as well....Im beginning to think the camera choice is wrong, but its the best compromise of features - i can wait for the weather proof housing and motion sensor for the TLC-200, but the output format is just too inflexible - I just saw adafruit had a weatherproof box with a clear front : perhaps an old canon powershot, CHDK and a massive box of AA batteries is the way!Wow! now that I write all that out, there was a massive amount I left out of the original post that wasn't obvious! a thousand appologies all: future posters, learn from my mistake - post EVERYTHING!cheers!

author: SeanB
author_rank: Super Contributor
timestamp: August 09, 2012, 06:21:54 am
content: Another thought is to open the case and wind a small coil of wire around the pir lens, around 100 turns of ultra fine wire, and then couple it via a 1nF capacitor to the output of the pyro cell, so that it emulates a pulse from the pyrocell. Then wind a 50 turn coil to matech and stick on the outside overlapping the coil in the case. This coil can be fed with a 20 pulse per minute current ( via another 100n capacitor) to trigger the inside circuitry. Should work well.

author: SockThief
author_rank: Contributor
timestamp: August 09, 2012, 06:40:10 am
content: Hi Sean,Ive been having a look at the design of the cam to see if something like that would work, im sure there is a line from the PIR to a micro that goes hi/low when the PIR is triggered, in which case a small switch run to the side of the case which can selectively override the PIR would be possible.However when I look at the case, and design, it appears that getting into that part of the circuitry without damaging the weather seal could be a challenge. Unfortunately I live in Sweden, and weather proofing electronics here, particularly during snow storms is a challenge, and so if I could do something without needing to crack the case open that would be ideal. But from a theoretical/Woz perspective its an interesting theory. Simple. Brilliant!cheers mate

author: SockThief
author_rank: Contributor
timestamp: August 09, 2012, 07:25:35 am
content: A couple of more bits of information if its interesting:Moultrie M100 Product Page:http://www.moultriefeeders.com/productdetail.aspx?id=mfh-dgs-m100Moultrie M100 Manual:http://images.ebsco.com/pob/Moultrie/catalog/M-100_Instructions-ENGLISH.pdfBrinno TLC200 Product Page:http://brinno.com/html/TLC200.htmlAdafruit Weatherproof Box:http://adafruit.com/products/905(would fit the brinno comfortably - epoxy a tripod stand on the bottom and you're good to go!)it's just such a shame the Brinno's want to output AVIs - but I guess it saves space to compress the files - still for a simple firmware addition to give the choice....

author: Skibane
author_rank: Contributor
timestamp: August 10, 2012, 03:31:05 am
content: Quote from: Rerouter on August 08, 2012, 11:32:08 amRemember the oldNational Semiconductor LM3909low-power LED flasher chip?It used to be a staple among hobbyists, way back in the early 1980's.It would flash a LED for years on end, using just a single 1.5 volt D-cell.The chip hasn't been manufactured in decades - but you can still occasionally find 'em on ebay.