Analog display for strain gage

Discussion in 'The Projects Forum' started by Wally6800, Apr 22, 2014.

  1. Wally6800

    Thread Starter New Member

    Apr 15, 2014
    I am building a glider that I want to auto tow for launching.
    I have been advised that I need a way of determining the tension in the tow line from beginning to end of the tow.

    The fellow that designed my glider told me that he had a friend that designed and built a device that measured the tow line tension using a strain gage that was connected to a box that was on the dash of the car that displayed the load on the tow line on an analog display. He was able to operated the system from that box. Turn it on or off, calibrate it and read the display on an analog device and a few other things that I can't remember.

    He thought he had a copy of the schematic that was used in building this system but he couldn't remember where it might be stored.

    I am a ME and the only EE training I have had is DC and AC circuits when I was in college.


    How difficult would it be to design and build another system ?

    Any thoughts , comments, recommendations or advice would be most welcomed.

    I have bee told by the designer that to try to launch with out such a system is very dangerous and don't try to do it without the tension display.

    Thank you for any assistance.

  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    Lotsa ways to skin this cat. PIC/Arduino, all analog, all digital, combinations...

    The starting point is the sensor. If you can get a make/model/part number, and maybe post a datasheet, the fun can begin. In the system you've seen, is the dash display a meter, or string of LED's, or what? Do you need to see a range of strain values, or just something simple like three LEDs (red= too heavy, green=midrange, yellow=released)?

  3. Wally6800

    Thread Starter New Member

    Apr 15, 2014
    I don't have very much to offer at this time because I had no idea of how difficult or how simple doing this system would be today. The designer seemed to thing it was pretty difficult when it was done the first time, about 30 years ago.

    The one thing I do know was that they tried doing it in digital output. That just didn't work because the tension on the tow line continually varies as the glider is launched. The digital read out changed so quickly that the driver couldn't read the numbers. They changed the readout to an analog device and it worked OK. I think they used a voltmeter and made a new face for it to show stall range (yellow), safe range(green) and do not exceed range(red). There was also some kind of calibration necessary.

    I will get more information and I will post answers for the questions that you answered.

    Thanks a million for the response. I always feel better when I hear someone say, " That can be done a couple of ways." even if I don't know how to do any of the choices.

  4. MaxHeadRoom


    Jul 18, 2013
    What kind of possible tension range/values are you looking at?
    The art of doing it digital is to control or slow the update time so it makes sense to the operator.