Secure door proximity sensor for wheelchair - Page 1
Forum section: electronics / general

author: Circlotron
author_rank: Super Contributor
timestamp: August 20, 2020, 07:24:55 am
content: I'm looking for a commercially made transmitter and receiver of some sort that could be attached to a wheelchair and used to open an electrically operated swing door.The parameters:1/ Transmitter and receiver to be paired for security.2/ Commercially made - no diy Arduino type stuff3/ Enclosed in plastic box, not bare pcb.4/ Relay contacts output - to switch 24VDC at several mA.5/ Transmitter to run continuously and rely on proximity, user incapable of pushing a button.Obviously with the transmitter running continuously there would be an issue with battery drain so it might have to be powered by the large wheelchair battery.Doesn't even have to be RF. Maybe even a camera scanning a QR code on the wheelchair?

author: Ian.M
author_rank: Super Contributor
timestamp: August 20, 2020, 07:29:32 am
content: Try googling: RFID access control hands free

author: JoeyG
author_rank: Regular Contributor
timestamp: August 20, 2020, 08:01:17 am
content: What about floor pressure mat, when the wheelchair goes over it , it turns a relay on?

author: nfmax
author_rank: Super Contributor
timestamp: August 20, 2020, 08:08:00 am
content: Sounds like an RFID application, with a 'passive' transponder on the wheelchair. Take a look at store anti-shoplifting alarm systems, or possibly even pet door (catflap) locks. See if you can find an RFID supplier who will talk to you, it sounds like there might be other applications with the same requirements.

author: Circlotron
author_rank: Super Contributor
timestamp: August 20, 2020, 11:43:01 am
content: Quote from: JoeyG on August 20, 2020, 08:01:17 amNot secure. Anybody could get in. This is for a door leading to outside.

author: Circlotron
author_rank: Super Contributor
timestamp: August 20, 2020, 11:46:57 am
content: Quote from: nfmax on August 20, 2020, 08:08:00 amI did think of those anti shoplifting things, but the passive bits on the item for sale would all be the same. The alarm end would respond to any of them, not just one unique one. The cat flap lock sounds good.

author: Circlotron
author_rank: Super Contributor
timestamp: August 20, 2020, 12:10:42 pm
content: Quote from: Ian.M on August 20, 2020, 07:29:32 amYep. I think that might be the one.

author: Ian.M
author_rank: Super Contributor
timestamp: August 20, 2020, 12:55:46 pm
content: As long as the card isn't shielded by metal on the wheelchair it should be good. Maybe register two cards and attach one each side of the chair with 3M VHB tape on the side panels so you don't have to have RFID transponders both side of the passageway. You'll still probably need one inside and one outside the door. Don't forget you'll also need some sort of high reliability proximity sensor to keep the door open till the wheelchair is well clear

author: Circlotron
author_rank: Super Contributor
timestamp: August 20, 2020, 01:07:22 pm
content: Quote from: Ian.M on August 20, 2020, 12:55:46 pmYep. I actually work for a company that manufactures and installs swinging and sliding automatic door operators, so there's no issue there. This one particular wheelchair situation we hadn't done before.

author: Ian.M
author_rank: Super Contributor
timestamp: August 20, 2020, 01:11:30 pm
content: So inside RFID sensor and outside RFID sensor. Door opens if either 'sees' a valid token, and closes again (subject to safety sensors) either on a timeout or when the sensor the other side of the door 'sees' the token.N.B. don't trust RFID sensors that maintain their own local database of valid codes. Some of them are far too easy to hack.You want a system with a RFID 'brainbox' (controller) containing the permitted access list, that can be located in a secure area, and sensors that just send the 'brainbox' any codes they 'see' preferably over a hard-wired encrypted link.