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Circuit Design with Sensors-Your Advice Needed

  1. Apr 19, 2012 #1
    Hello everyone,

    I'm Jamie and at the moment I'm at the final stages of my final year design project. I'm designing a piece of exercise equipment that motivates children to exercise but have run in to a bit of a problem with regards to the circuitry.


    The image above shows the finished product. The user stands in the area marked with the red X and has to put their hand or leg through different holes as they light up (illustrated brilliantly with the blue lines). A sensor located on the outer ring of the hole detects the users' hand or foot and deactivates the light and randomly switches on another set of lights until they are deactivated by their respective sensor, and so on.

    Any advice on the circuit design, problems, type of sensors needed, programming etc. will be greatly appreciated. Any help will be acknowledged in the final report and folio :)


  2. jcsd
  3. Apr 19, 2012 #2
    I think this is a good idea. I am into exercise and martial arts, I don't mind having one for reflex and target practice!!!

    OK, this is really not my field, but I am just join in for the fun of it.

    1) If you already find a way to light up the circle around the hole, I would consider putting two light detector diode in each hole. The detector diode has to be sunk deeper into a hole and point to the light on the circle and only detect very limited angle of light. The detector is made pointed at the lighted ring. So it mainly detect the light of the ring. I am going to use micro controller to null out the ambient light.

    2) The two detectors are at 90 deg from each other so it sense a cross pattern of the hole. Either one of the detector detects a blockage of light, it trigger the micro controller.

    3) I am out of the job market for a few years, there might be better micro controller. The last one I used was by Analog Devices ADuC831. It is a 8051 based controller with serial bus, MUX ADC and DAC. It has built in EEPROM and RAM. Pretty much one processor do all. Programmed by I^2C EEPROM.

    4) For detector diode, use typical op-amp in transimpedance configuration to transform the current output of the detector diode into a voltage. Since you have so many holes, you need a analog MUX IC to multiplex the signal to drive the ADC input of the controller.

    5) To light up each ring, you just use the output port of the ADuC831 and some sort of light driver to drive it. The program can turn each on or off as will.

    6) To null out the ambient light, program the ADC to read the output of the detector without having the light on and with the light on to set up a base line. Then you can tell whether anything blocking the light in different environment.

    The rest is up to your programming and imagination. There got to be other better way for detection, but I think the concept is similar. Using a micro controller will do most of it. Analog Devices has a whole family of this kind of controllers with different number of DAC, ADC. You don't need DAC, so maybe you can find one with more MUX ADC input to save the trouble of using an external MUX that need my circuit and programming.
    Last edited: Apr 20, 2012
  4. Apr 20, 2012 #3
    This should be straight forward using only digital electronics. Using a microcontroller (maybe using a PC and USB-connected board would make it easier) you can control the different holes, that light up just using several LEDs.

    To detect human interaction with the holes, i believe the easiest thing (also getting a nice result) would be to use passive infrared sensors. Just have an infrared source and a receiver with equivalent frequency (you should just buy them in pairs so shouldnt be a problem).

    ... might depend on what equipment you have available? Using Visual Basic or LabVIEW would be an easy solution if you are provided a bit of extra hardware (can be a bit expensive ;D)
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