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Request for help – short range obstacle detection alarm

  • Ian D Midgley
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John Wheeler of the Salisbury panel writes:

I have a blind wheelchair bound client with an inert leg protruding forwards on a metal support and the support has to be removed regularly.  When moving himself about in his room/trying to get through a doorway etc his foot knocks into obstructions, so he needs a device that will warn him that an obstruction is near, & ideally roughly where. I’ve tried a car reversing kit with several sensors but it starts to sound a “beeper” when a metre away & can’t be made less sensitive. Finding a suitable sensor kit on the internet is proving difficult as suppliers are only interested in major industrial applications. Currently the best solution is stopping, waving a stick about & reacting accordingly. So has anyone solved a similar problem?- any kind of possible solution welcome!

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5 responses to “Request for help – short range obstacle detection alarm”

  1. Q Thurtle says:

    I would echo (pun intended) PeterP’s comment. Once something similar to the following sensor SRF005 (£11.99) was hooked up to a microcontroller like a PIC 16F88 (£2) and a handful of components (£10 ?), it could be adjusted to provide almost any form of audible indication (eg quiet and gentle low pitch for a distant object to louder and higher frequency for nearer objects: Or a spoken distance – slightly more costly). It could all be battery driven in a hand held/wheelchair mounted case.

  2. Joanna Clark says:

    I’m afraid i don’t know much about this area but I happened to come across this on the internet in case it is of any relevance for your wheelchair user who is blind and needs some warning of obstacles.

    Maybe the idea could be adapted if it can operate in confined surroundings.


    A team of British engineers have got together to re-design
    the UltraCane, the sonic walking cane that warns users of
    obstacles ahead of them. The newly designed UltraCane
    has a warning device fitted into the handle, which vibrates
    when there are obstacles ahead. The rate of vibration
    indicates how near the obstacle is. It is apparently much
    more reliable and easier to use than the original UltraCane.
    Further information from or telephone
    01423 359711

  3. Tony Samson says:

    Having read the earlier comments the one that has sensors at each door informing the client where he/she is seems the most viable to me.

    Having no electronics background myself my thoughts went along a more mechanical warning viz in the USA large cars were fitted with metal “whiskers” at each corner of the car at about kerb level so that when the driver attempted to park the car between two other cars he/she could hear whether he/she was scraping the curb or scraping against the neighbouring cars. Could some discreet audible bell/chime device be fitted?

    Tony Samson Tyne Panel

  4. Alan Hart says:

    Alan Hart from the IOW
    It appears the picies do not carry across in this format so you only have the text. I hope you understand without the pis to help you.

    Interesting case. I am puzzled that the sensors are not sensitive enough when allegedly they can tell down to an inch (Christian measurement!) I was uinder the imprerssion the noise generator changed pitch the nearerer it got to an obstruction.. I was always taught to look for the obvious is there an adjustment diode or something that can be changed for pitch or distance?

    Looking at a wheelchair with the leg extension, it seems to have two probes on the end so these could be used as ‘fixings’.

    1 My first thought is a set of bumpers a) to project his foot, and b) to prevent impingement on the door frame or wall.

    A strip of brass say 1″ wide by 0.062″ thick bent to form a bumper strip around the end of the wheelchair. The strip is attached to the wheelchair. Make a second piece from say 0.25″dia brass bar bent to the same shape as the brass strip. Mount the bar to the strip with spring loaded screws of non ferrous material (Plastic as used in kitchen cabinets).

    1A An alternbative is to join the two together with non conducting nut bolt (plastic) and put foam squares between the two conducting parts. Foam or soft rubber can be stuck on either with a good adhesive. In fact it may pay to have two strips rather than a rod and strip.

    Using some isolation mounts (So the fixing does not make contact with either strip) fix the ends of the brass strip to the wheelchair. The mont could be something like a flexible door stop. There needs to be the smallest gap possible between the rod and the strip.

    The idea here is quite evident. The rod impinges on the obstruction and the spring mounts allow the rod to move. The brass rod then touches the brass strip completing a circuit with a noise generator giving the warning. If you don’t want to fix to the chair (with some quick release system for fast removal), you could fix it to the leg extension with just a bumper shape rather than an all round leg shape.

    2 I suppose you could use the existing sensor to guide him to the hole in the wall which would then tell him to slow down so he doesn’t smash into the frame causing permanent deformation of the bumper. So a consideration here is the strength of the brass bar. I use brass because its good contact material but there is no reason why you could sue a scrap car bumper with some form of spring arrangement to the front the only provision here is the spring is insulated from the bumper so when the spring and bumper touch you have a contact to operate a buzzer. A different buzzer sounds for each corner will tell him which way to go to avoid the obstruction. Again fix to the leg extension of the wheelchair.

    You are right about there’s not a lot of ‘range finders’ for the visually impaired perhaps a visit to the local RNIB could sort something for you. In the meantime back to my brain storm………….

    3 May be a drummers wire brush on the end of the leg extension, one either side with some form of bell on the end so when the brush is moved it rings

    4 A more radical approach is to get remote door bell pushes and fix those to the door frame with a spring from the door frame covering the button suppose you could use the same ‘bumper’ arrangement

    The only problem you have here is the electronics related to the receiver. If you have an electronic man you will have to change the sender (Bell) output to the same wavelength of a single bell. or you have different bells for each doorway which will be quite bulky if you have ten bells on the wheelchair. If he hasn’t enough problems already adding deafness will not endear him to you! However moving on…..

    5 I believe the RNIB have a programmable PIR which could be set up on the doorway. I had a case of a lady who was blind from birth (So was comfortable with blindness) but had a stroke and had lost her special awareness. I rigged up a PIR on each door frame so when she broke the beam a talking message would say ‘You are in the lounge’ When she broke the second PIR on the door way (Two on the door frame one each side of the door frame) it would say ‘You are in the hall way’ The when she went to the next door and broke the beam it would say ‘You are in the hall way’ then ‘you are in the kitchen’s Etc. It worked OK but the lady moved to live with family so we never installed it and it has long gone to the big dump in the sky.
    Positioning the PIR would be critical if you pursue this idea. You will have to protect the PIR with some form of shield to stop any damage unless you site it above or below the leg extension position.

    You might get some ideas for further thought from this

    I hope this helps

    Regards again.
    Alan Hart
    IOW Panel chairman

  5. PeterP says:

    You need to look in the amateur robotics world for low cost short
    range ultrasonic sensors.

    is a page full of them from £11 upwards.

    You can even get a servo driven tilting bracket to allow them to scan
    in elevation or azimuth depending on how you mount it. explains the

    The SRF05 at £14 inc VAT with a minimum range of 1cm looks promising
    – a fairly simple PIC interface could decode the return range pulse
    into a sliding audio scale depending upon range or a simple on/off
    warning. We have a umber of people with PIC skills in various panels.

    Depending upon the type of ranger the interface module can handle
    many controllers. Typically ultrasonic sensors have a beam width of
    about 60 deg so if you need 180deg coverage you would need 3 fixed

    You could also use IR if you are not interested in above 100cm.


    The GP2Y0A21 at £7.99 ex VAT has a range of 10cm to 80cm.

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