Touchless Technology with ultrasonic distance sensors


The concept behind this circuit design is that you can press buttons without touching them. As your finger lowers to the tabletop, the yellow light will come on, indicating that you are on the correct approach. Farther down, the green light comes on, which activates the button function.

Or so it’s supposed to work. What I find is that when my finger is on the lower level, the upper sensor will still detect its position, which is bad enough, but since it’s measuring at a diagonal, it will measure the distance as greater than it is.


Possible solutions would be to redesign the circuit so that there is a UDS pointing up from each button position. But that would require four sensors rather than two even for this circuit.

Hmm, I wonder how big the ‘spray pattern’ is for the sensor pings. If it’s fairly wide, then the position of the finger could be determined by triangulation.

Available on Amazon:

Vivotech Hc-sr04 Arduino Ultrasonic Distance Measuring Sensor

Arduino Cookbook (2014 edition)

About engineerzero

Once and future engineer.
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4 Responses to Touchless Technology with ultrasonic distance sensors

  1. engineerzero says:

    Oooh — just had a headsmackingly obvious thought! Why not simply compare the distances measured by the upper and lower sensors, and whichever distance is shorter is the one that counts, as obviously it would be on a direct line with the finger position. Something to check out next time!

  2. Marcel says:

    Hi there! My name is Marcel and i live in Luxemburg. I work in a home for disabled people and i’m searching for a cheap way to activate electric slide doors from toilets and other rooms. The people have dificulties to press the push button, so i though that capacitive touch switches could be the solution, by glueing a copper foil from the size of 10 by 10 cm on the door frame which the y would simply touch to activate the touch switch to open the door.
    But a touchless solution would be even better, as an ultrasonic sensor is quite cheap(we have 46 of these doors and we need 1 sensor for each side)
    I was adicted to electronics 20 years ago but i didn’t finish school, so i can’t design electronic circuits.
    For the ultrasonic sensor, do we really need an arduino for such an application? What is the easiest way to use the ultrasonic sensor to activate a relay? (without the arduino, but if you say that we need a microcontroller, what about the TEENSY?
    I thank you in advance for every information you can provide.

    Best regards

    • engineerzero says:


      It’s possible to transfer many sketches from the Arduino to an ATTiny. The ATTiny is MUCH cheaper at a price of about one dollar each.

      Here is an Instructibles on programming an ATTiny85 for an ultrasonic range finder:

      The sample code in the Instructibles is set for two inches, but I think this is just a matter of programming. I have gotten sensors to detect out well past a foot on my tests.

      Make sure you shop around for the best prices. On, ATTiny85s and ultrasonic distance sensors are both going for a dollar each, or only four dollars per door. While that is encouraging for your project, remember that they will require DC power supplies, which are running about six dollars each on ebay. The good news is that you should only need one power supply per door. If your door mechanisms were already employing DC, then you probably won’t need a separate power supply for the chips and sensors as the power requirements for both are very low.

    • engineerzero says:

      As for having the chip activate the door relay, it depends on the relay. You may need a power transistor or thyristor as an interface.

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