Nov 062018

Had an interesting request from an OT today. The scenario is a client with epilepsy who also has a learning disability and an impaired level of mobility (poor balance/stability). The requirement is a sensor at the bottom of the stairs and another at entrance to the bedroom so the parents are alerted when he is moving about upstairs (or about to go upstairs) so they can supervise – but that only alerts when the client is moving as opposed to anyone else. This implies a proximity system based on something the client wears and would trigger the sensor within (say) a few feet.

Ideas I’ve been mulling over are:

A simple infra red transmitter that pulses every few seconds to conserve battery life. This might work (perhaps in the form of a device clipped to clothing) but the IR could bounce around and trigger the sensor from a greater distance, or if focused (or obscured by the client), could miss the sensor altogether.

A 433mhz band transmitter of the type used for simple remote control switch applications. But not sure the range could be attenuated to the point it would only work at a few feet.

Passive RFID tag – the range of operation is way too short. i.e. the tag has got to be very close to the sensor as there is no internal power.

Active RFID tag/active reader – the readers tend to be very expensive and the range will end up too great.

Any other ideas welcome!


  19 Responses to “Detection of client with epilepsy when near stairs”

  1. So as described I think one of these low power bluetooth modules would work:

    They are available for £25 each from RS (885-5820). Triggering range is selectable, one option is “near” which is about a metre. However I would not use them with the phone app but rather use them as a convenient source of the hardware. The client would carry one and the others would be set up as beacon/detectors. Either hardwired to the alarm or connected by bluetooth. It does require someone familiar with embedded electronics to implement. There may be more off the shelf solutions, asset tracking is something to search for.

    An alternative approach is something that detects everyone but only goes off after a few seconds, during that time the parents can disable it for enough time for them to pass (by pressing a hidden button or similar).

    Otherwise I like Chris Dale’s idea of using a reflective IR sensor combined with a retro-reflective marker. Apart from retro-reflective bicycle clips you can buy the fabric to make a comfortable ankle mounted sleeve or build it into clothing, you can get this stuff in grey, white or even black variants. Also as a self adhesive.

    Face recognition is possible with a webcam (even on a Raspberry PI) if you have any programmers in your group.

    Oxford Panel

    • Thanks Graham – will take a look at the Bluetooth kit.

      Given his parents need a bit of advanced warning, the delay option might not fly (depends on house layout I guess) but will take a look when I visit.

      For the sake of a fiver, I have a IR sensor module on the way to test Chris’s idea as probably my first step. I’ve since been told the young man has some sort of equipment he carries on his belt but that might be obscured by his arm.

      • Rather than a delay, they could press something before moving into/through the area and be given an amount of time to move past the sensor (a optical interrupter would work best for this) or even hold a button as they pass. This could be a bit of a pain, if the parents are significantly taller than the client then there would be the option to add second opto higher up to make it more automatic (or a PIR higher up with a slightly wider field of view.) Then it is simple logic, if only the low sensor triggers then sound alarm, this could be done with a relay or a logic chip.


        • I’ll check what they might be willing to put up with Graham. The height one is an interesting concept – thought it would need some timing work on the logic to allow for the fact that if a couple of beams are used, they won’t both trigger (with someone tall) at the precisely the same instant. Thanks.

  2. work well have them in my workshop to trigger 12 volt lignthing in dark corners… at 7 quid a pop excellent value will work of 9 volt battery and small buzzer.

    • Thanks Jim – good cheap little module, I’ll remember that. Unfortunately, the requirement is to trigger specifically when the client goes past.

  3. There are so many ways that this could be done, including the classic passive “frequency doubler” archway, beloved by supermarkets and department stores everywhere, and the active transponder.

    But have you considered the “bathroom scales” approach? Provided that no other member of the household has a similar weight, a very simple mat sensor incorporating two metal sheets and a (thin) bit of “antistatic” foam between them will do the job and can be low profile enough not to be a trip hazard. As they stand on the mat, the resistance changes to “their” value and a simple range gate will trigger the alarm.

    Otherwise, I’d go for the frequency doubler.

    • Hi Keith – I don’t know much about the shop systems – but those anti-theft RF tags are small and passive so I assumed that’s why the loops were so big. I take it there is a battery powered equivalent tag that could shrink the detection hardware?

      The weight one is an interesting option too if it could handle someone walking quickly across it.


      • Royal Mail certainly uses one (a longer range battery powered tag) to track test letters through its systems for quality control.

        The speed of walking won’t be a problem unless there are other family members with a similar body weight.

  4. Hi Ian, one of our engineers is working now on exactly this problem for a client of ours in a wheelchair. They need to know when the wheelchair leaves an area. He demonstrated a rough working system last Friday at our meeting. If you like I will get him to contact you.

    • If you wouldn’t mind please Peter, thanks. All my details are under Harrogate and Ripon.

  5. What might work is an infrared source with a detector mounted next to it instead of opposite it. The detector would be shrouded so that it could only ‘see’ across the foot of the stairs etc. The client would wear two or three slightly convex reflectors on the side of his clothing or sleeves. Alternatively he could wear reflector(s) of the type one might find on the front of a bicycle. The alarm would be triggered when the detector detected the reflected infrared source.

    • Interesting thought that Chris, thanks – and actually easy to do I reckon as there are plenty of ready made IR sensor/receiver combined modules for close proximity applications, such as hands-free turning on of taps and loo flushing. They normally have a short range as it’s reflection off skin – but I bet if even a simple reflector is used outside of that range, it might well trigger at a much greater distance. I feel an ebay purchase and some experimenting coming on……!

      As you say, if it’s convex, it will scatter nicely and stand a fairly good chance of the receiver picking it up. Trouble will be where to put it on the client to get consistent results. Thinking side of the shoe might actually be favourite……

      This doesn’t deal with night time – but nothing wearable does really, so I’m thinking separate IR beam solution across bedroom door for that, which is just turned on at night.

  6. Lo-tech using child gates at top and bottom of stairs ?

    • I’ll check Jack – but I get the impression he’s going to be old enough to bypass standard stair gates and he’s used to moving around. It will get to the point with bigger kids where even locking them won’t help as there might be a tendency to clamber over which might increase the risk. The problem is that some kids just have no comprehension of risk to themselves.

    • Or perhaps go ‘bio” with a ‘helper’ dog that is trained to respond (bark) at either stair-top or stair-bottom. The ability of dogs to assist human requirements is outstanding

  7. What are used in care homes, where inmates have to be tracked ?

    • Hi Martin. Active RFID systems are used for tracking assets as they move around a process within a building. I’ve never come across anything in use in care homes (i.e. you would tend to secure or monitor the doors as its easier) – but if such a system was required, it would probably end up using the same technology. The trouble is, it is more for checking roughly where something is, rather than proximity to a specific point. Expensive kit too.

      PS – according to the news this morning, HM Prison Warren Hill has started referring to its prisoners as “residents”, and cells as “rooms”. I bet that went down well in care homes up and down the land! 🙂

      • Your PS. Calling cells ‘rooms’ and prisoners ‘residents’ was introduced at New Hall women’s prison around five or six years ago. Curiously, many prisoners did not like it at all.

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