Door Direction Sensing - Page 1
Forum section: electronics / projects

author: ARico08
author_rank: Newbie
timestamp: February 03, 2016, 08:51:16 pm
content: Hello all, first time posting in the Forum so if I'm doing something wrong please let me know.So I have a project I'm working on that is a kind of smart security system that knows when you leave/enter a room so that it can adjust its security rules based on it, i.e., you just entered the upstairs bedroom so if it sees a window open in the downstairs kitchen there might be a problem. The biggest issue I am having with this is figuring out how to tell what direction someone has passed through a doorway. I can tell when the door is open or closed using reed switches much like a conventional home security system, but not if you've left or entered the room in question.I've considered using a series of beam sensors, like what would be in an optical encoder, but across the whole doorway so that when you pass you trip each sensor in a different order depending on if you are coming or going, but I'm not sure how well that would work.Any help or tips would be greatly appreciated.Thanks!

author: Paul Price
author_rank: Super Contributor
timestamp: February 04, 2016, 12:38:19 am
content: One of the hardest things to tell sometimes, my father once told me, is to know whether you're coming or going.One way is to use ultrasonic ranging readings to determine if someone is going towards or away from a door.Another: use a small thermal motion sensor(as used in the body-temp infrared detecting automatic light switches) to detect which side of the door first senses a warm body(human) approaching.Or use two closely spaced infrared/laser/LED xmit/receive beam-interruption pairs, closely spaced in a horiz. plane to determine direction of movement by detecting which beam is broken first. Beams should be at knee height to prevent swinging arms confusing detection while also avoiding detection of small pets.Or use a pressure-sensitive(easy enough to make and use the touch sensitive module built into a PICC or ATMEL or ARM MCU) with a thin DIY foil-plastic sheet capacitance pancake hidden under a carpet to detect the delta-capacitance movement of unexpected visitors.But you're overthinking the problem, if only one single thermal movement detector in a room detects things that go bump in the night, that shows any unexpected movement, then it must be that from this evidence you can conclude it was probably not due to a ghost.Haven't you ever seen any of several glamorizing theft while cleverly showing the defeat of the best of security protection, i.e. flicks about holiday bank robberies, James Bond's clever break-ins or escapes or even any of the many sophisticated art theft movies showing how midnight burglars ravage a museum and steal something like the Hope Diamond?

author: SL4P
author_rank: Super Contributor
timestamp: February 04, 2016, 07:07:04 am
content: A friend did this about 20 years ago for a big oil company - (effectively) using RFID tags.They were the 'long-range' proximity tags & readers used to access buildings etc.A loop was placed about a meter either side of the door (looped around the hallway - not just the wall, floor or ceiling)The relative timing of the tag detection gave the direction away, but these readers were also smart enough to detect up to five or six tags moving simultaneously through a door (e.g. you, your girlfriend, and the dog) - which solved the problem if one person opened the door, then held it for someone else going the other way - etc.The tags were also covertly attached to valuable assets (computers etc) - so they could track who was moving with them in or out of the building. Surprisingly, this was before widespread CCTV coverage!I've never seen another system like it since -- but it was fun to work and brainstorm on.

author: CaveMannDave
author_rank: Regular Contributor
timestamp: February 04, 2016, 08:28:57 pm
content: Hi:Look athttp://www.ebay.com/itm/Microwave-Sensor-Module-10-525GHz-Doppler-Radar-Motion-Detector-40mA-for-Arduino-/3115126411421 per door, concealable, cheap, use as much signal processing as you need.Cheers,Dave

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 04, 2016, 08:38:09 pm
content: I work at an industrial campus with over 10K people. Virtually all of us use our RFID badges to pass through gates, portals, doorways, etc. They use a box on either side of the path with what appears to be IR filters (dark red plastic). They can reliably tell which direction you are going. If you are leaving, no problem. But if you try to enter without swiping your badge the door doesn't unlock, or an alarm goes off alerting the security forces.I am assuming it uses IR technology, but it might use RF. The security people would take a dim view if I tried to to any research into them.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 04, 2016, 08:44:03 pm
content: Passive IR sensors. No RIFD tags needed, no microwave emissions from some Chinese no-name box, simple and cheap. Put one on either side of the doorway. Done.

author: ARico08
author_rank: Newbie
timestamp: February 08, 2016, 04:34:48 pm
content: Thanks everyone for the suggestions! I think I am going to give the PIR sensors a shot. For those who have worked with them before (I've only used the pre-packaged modules for things like the Arduino) would you suggest the dome ones like thishttps://www.adafruit.com/products/189or should I try and use an IR sensor and shoot an IR beam across the doorway?