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Wireless key fob and USB receiver. Advice sought

Discussion in 'General Electronics Discussion' started by Ray Pooley, Jun 3, 2017.

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  1. Ray Pooley

    Ray Pooley

    Jun 3, 2017
    Hello forum users. Newbie here.

    I will give you the scenario. I have a building with 5 staff and 3 doors. I want to be able to monitor when they pass through the doors. It's so there can be no dispute as to how long they have been on the premises, as you might expect. I know there are commercial solutions out there but they are pricey and I don't have the money to spare. What I do have is a background in mechanical and electrical engineering and software development. So I am looking to develop my own system from basic components. If I can buy a programmable fob that can be assigned a unique id, a transmitter/sensor (for the doorways) and a USB receiver for a PC .it would be a good place to start building a prototype. Does anyone have any idea where I can find this sort of stock or, indeed, whether these things exist at all? Thanks in advance.
  2. Bluejets


    Oct 5, 2014
    I think there is a lot more to the requirements here than you seem to be aware.
    Just as an example. What happens if they all ( or one or whatever) enter or leave by one door at one time.
  3. ChosunOne


    Jun 20, 2010
    Good luck with that, Ray.

    (1) Are you thinking of installing electronic locks on the doors, to be opened with the key fobs? (Access Control)

    Or sensors on the doors to trip local annunciation/alarm if the door isn't first shunted/bypassed by the fobs? (Alarm System)

    Full disclosure, my field of expertise is by far more security alarm systems than access control, although I've worked with both; and they have enough common ground that I can see potential problems with designing your system, whichever way you go. In both cases (alarm or AC), it is by FAR easier to prevent entry by intruders than to prevent insiders from sneaking out.

    (2) Bluejets's question points out one of the hazards of access control, called "tailgating", where one or more people tailgate behind someone who has properly accessed the premises. A proper access control system has a protocol to discourage it, but I won't get into it because it's a little more elaborate, won't work with an RF (wireless) key fob, and I still don't know how you want to approach the problem {See (1)}.

    Another problem with key fobs to track who's here or away is,
    (3) Does anybody besides your staff need to access the building during working hours? Are there deliveries? Visitors? Does anybody ever order Chinese, Thai, or pizza for lunch (or whatever you guys do in the UK)? Assuming one of the staff has to let someone in, his/her fob is registered as being used, but it doesn't mean s/he left.

    (4) If one of them wants to sneak out for a couple of hours, is it feasible to fob the door and exit, wait a couple of minutes, fob the door again, maybe open it but not enter, (depending on how you set up the protocol). and later claim s/he stepped outside for a couple of minutes. S/he can do the same routine a couple of hours later, or even have someone else fob the door, who can claim that s/he also needed to step outside for a couple of minutes.
    And, yes, if you have staff who are cheating on you, it has been my experience that they will try to game the system if it has holes in it.

    I'm guessing you've already considered installing CCTV, with DVR, on your staff's work stations and/or the doors and rejected it as too expensive. However, it might be the most cost-effective way to approach the problem that actually works.
    BobK and davenn like this.
  4. BobK


    Jan 5, 2010
    Very good analysis, ChosunOne.

    When I worked at Intel (now retired) off hour access was through a floor to ceiling turnstile that looked more like a torture device than an entryway. This was more to prevent tailgating than accurate determination of who was in the building, but, coupled with a badge reader on the inside it could have served that purpose as well.

  5. Irv


    Jun 7, 2017
    If I read this correctly, you just want to track the time(s) they are on-site. Not control their access,
    nor prevent others from coming and going, correct?

    Simple mercury in a tube motion detector plus a wifi chip in a fob. Router can tell when each chip is within range, you could write a small program to work with those logs and produce reports. Motion detector assures they didn't just leave the fob behind (or warns you they're dead :O) Limited wifi range means they can go for a smoke, but probably not much further.

    Of course, once they find out about this, they're going to select one person to juggle all the fobs, while the rest leave for a long lunch hour.

    Obviously, if more security is required, or you need to know which doors they use, then rfid card readers and door locks would be needed.

    360 degree fisheye camera on the ceiling is probably the only solution that would work and not make employees mad. Call it a burglar/fire detector, and don't let them know someone is watching them.
    Last edited: Jun 7, 2017
  6. MrBellisarius


    May 8, 2018
    Hi Ray, did you eventually find a solution, a Key fob where the receiver gives you the serial number and button pressed rather than discrete outputs?

    I've been trying to find the same (albeit for different reasons) and it's not easy. I'm prepared to program the uC in the transmitter myself if necessary (I am a firmware engineer with ICE toolchains for AVR and PIC), but I would like to have a fully tested and approved RF design.

    Seems incredible that nobody actually offers this.
  7. ChosunOne


    Jun 20, 2010
    As I noted before, my real expertise is with alarm systems, but I have more than a nodding acquaintance with Access Control systems; and I'm pretty sure that commercial companies do offer what Ray needs, but it's not cheap. Access Control usually costs more than alarm systems. Even most professional-grade home alarm systems routinely identify and log multiple Users' keyfobs along with Event/button (arm, disarm, other functions including output to lock/unlock door). Technically, a medium-end home alarm system (professional-grade) can serve as a rudimentary access-control system, but an access control panel that can distinguish the difference between entering, exiting, and activating but staying inside (to permit customers or deliveries to come and go); and can prevent tailgating, is not a rudimentary system.

    Also, stipulating key fobs greatly complicates the issue because, unlike prox(imity) or card readers, an RF receiver can't tell if a signal comes from inside or outside. But I might be out of date on this one. It's been awhile since I played with an access system.

    I was prepared to get into all that with Ray, but he never responded after the one post.

    Just because I'm a compulsive nit-picker from professional habit:
    Not that it matters, but the receiver only receives signals from the RF Keyfob and passes them on to the Control Panel. It's the Control Panel that processes the signals and decides what to do with them: Disregard/accept, identify, response, log event, and print out (optional) and whatever else I didn't think of, off the top of my head. Key fobs in my industry usually send multiple information in each transmission: (1) ID of transmitter (=ID of User), (2) which key/button was pressed, and (3) sends a low-battery signal if battery is weak.

    Edit: Everything I said is true in North America. I have to admit that I know little about alarm systems and access control in the UK and Europe, except that it is different in some aspects.
  8. MrBellisarius


    May 8, 2018
    That's the bit that's missing. I'm more than happy to process the signals from the keyfob, the problem is that ALL the many 4 button keyfobs I have found that use rolling codes use the Keeloq system with a custom manufacturer code.

    ALL these suppliers provide their own decoder that provides 4 discrete outputs.

    The problem with the Keeloq system is that the manufacturers code must be kept secret or the integrity of any system built with that code is comprised, so it's quite natural that manufacturers do not disclose the codes they use with their own decoders. They do offer to program custom codes, but we are talking a hundred pieces that does not make that viable.

    I'm sure somebody must sell generic keyfob transmitters for this type of use!
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