selection of proximity sensor

  • Hi guys.

    For one of my university projects I need to detect the presence of a person in the shower. In order to do that what I have in mind is use a proximity sensor. If the target is in a distance range (let's say 20 to 50 cm) It will assume that the person is in the shower when the distance measure is no longer in this range then it will mean that the person left the shower. I need to detect all the time of the person in the shower (meaning when he/she gets in and then out). I have read a lot of info and forums to properly choose the type of sensor. However I still don't have a clear answer. About the Ultrasonic proximity sensors I know that they are cheap and more accurate by it can be affected by Temperature, humidity and some ambient noise, all of them which happen in a shower. The other option an Infrared one gets affected by lightning conditions and the surface of the target, and it doesn't have a linear output. The last option I checked is a PIR sensor I know it senses Temperature of the target, but I don't know if it will be affected by the running hot water and also is more expensive. In general, I don't know how the running hot water will affect the detection of the person in shower. Also,so again I don't know how this will work. Sorry for the huge amount of questions, I am a little bit confuse with all the factors to have in mind. I am hoping someone out there can help a lost newbie like me and give me a suggestion. Thanks a lot 🙂

  • Mod

    @mcamiea Have a look at a radar sensor.
    Default sensing range will be much more than 50cm, but sensitivity can possibly be reduced.

  • Hero Member

    @mcamiea I am using the GP2Y0A21YK0F (complicated name😄) sensors. These are active infrared (as opposed to PIR passive infrared) and do have a linear distance response (if connected according to the data sheet)

  • @mcamiea

    A weighing sensor in the floor perhaps?

  • @mcamiea
    Or a contact sensor / weighing sensor / pressure sensor on the floor?

  • @boozz I thought about it but the waterproof seems like a probable issue here. I didn't know if there were any waterproof sensor of this type, and then the cables maybe a safety issue, so I moved to a proximity sensor located on the walls or roof.

  • Hero Member

    What are you actually wanting to achieve?

    How long your kids are taking a shower for?
    If they actually did have a shower vs "Yes dad I did have a shower...I promise"...but really didn't?

    I ask as there are other methods to make assumptions that someone is in the shower...

    eg: Humidity sensor to detect the steam...
    Or temp sensor on the shower rose which heats up when the hot water flows...

    You could use a light beam sensor set at waist height. These are easily waterproof and robust and cheap.

  • @AWI Oh really? I read somewhere that the IR output wasn't linear, will check again. thanks

  • @gregl It's a university project. To play some sounds strictly while the person is taking a shower, and needs to be activated automatically, also turn off automatically

  • Hero Member

    Ok cool...

    Does it need to be durable in the installation (last many years) or just for the duration of the project? Either way id probably go with a light beam ( IR ) break and robust.

    I got to admit im really curious as to what noises you will be playing to the person taking the shower!

    I dont need these sensors... my kids all sing in the shower so i know when they are in there 😉

  • Hero Member

    @mcamiea The GP2Y0A21YK0F is almost linear if you take the inverse (reciproke) of the output value:


    It is not waterproof but can withstand enough if you mount it right and seal it.

  • @mcamiea
    While showering this evening I had to think about your project. Multiple sensors will do the trick, some better than the other. Maybe a combination of sensors (even cheap ones) can be used I think.

    1. Using a DS12B20 temperature sensor on the hot tap gives you an indication that someone uses the shower. A steep increase of dT/dt tells you that someone has started the shower (assuming that nobody would shower with cold water 🙂 ). If the sensor is above a certain temperature and/or stays high, than the hot water flows. a sudden decrease of dT/dt tells you that the hot tap is not in use anymore. The shower has stopped
    2. An infrared LED can be used at pretty high currents, expecially when you do that for a short period of time. a tiny hole, some 2-component glue or other adhesive will be enough to fix the LED in one of the walls in the shower. Combine this with an IR sensor (IR sensitive transistor or like) at the other wall and the first light-beam has been created. Switch the LED on and off, and simultaneously read the IR-transistor at the other end. You could easily get multiple pairs of IR-LEDs and IR-transistors to get more than one 'channel'. This will help in determining false-positives. (e.g. at least 3 out of 4 pairs must be high to start Mozart, Red Hot Chilli Peppers, or Buena Vista Social Club)

    Above mentioned solution will be cost effective, cheap and can be installed without hard labour. It will be rubust as well, and as it is low-voltage, will not electrocute one of your shower volunteers.

    I like showering.



  • @AWI Hey I did buy this Sharp Sensor, now I am trying to get the data of the cms, using the chart that comes in the datasheet that is the same one you pasted here. However it seems I am doing it wrong because the centimeters I am obtaining don't match reality, Could you please tell me which relationship you used? thanks

  • Hero Member

    @mcamiea I started with This tutorial. If it is still not clear let me know and dig the setup from the bottom of my drawer.