Was done enjoying Friday afternoon      

'hackathon'  at  WIN Enterprises Inc.     
17.44.1 Induction meter, as simple as possible.

  Introduction: This meter can measure the inductance of the coils in a wide range of 1uH - 200uH, using 0-10mA DC meter & LED driver from Solar Light.
  Why: In my 'home lab', I needed a simple, one range, inductance meter that quickly measured a small inductance. And of course in an easy way, avoiding 74xx, 555, micro controllers, arduinos, etc.
  Basis: The L-meter is based on LED driver, which is a simple pulse generator with an output transistor. Each pulse charge the measured inductance (Lx), which is then discharged through the LED and DC meter.

   The accuracy of the measurement will depend only on supply voltage (1,25V in this case). 
   For tuning, you only need to select the inductance of coil L1, until the arrow points to the end of the scale with short over Lx. I took inductance 47uH, and rewound a few turns, until it happened.

  For the final calibration, it is necessary to make a measuring inductance. This is easy if you know that the inductance of the coil is proportional to the square of the turns. I did this.

  It remains to transfer inductances (measured or calculated) to the meter scale with a pencil, scan the result, fix a little in Photoshop, and the new scale is ready to go. Finally, it should look like.

  The only drawback is that the scale is non-linear with zero at the end, & you must make it yourself.

  The voltage regulator 1,25V goes beyond this article. I do not have LM1117, and did not find anything better than cutting the complete regulator (step-down converter) from old SATA HDD board.

  A good thing is that it fits in the 2-AA battery holder, together with power switch and green LED.

  The last and simple operation (which takes more time than expected) is to arrange and fix everything between two pieces of transparent acrylic. In the photo, the finally assembled L-meter, which measures a coil with inductance of 7,5uH.

And this is where fun is just beginning. Two bags of coils will make you busy for the whole night.

  The basic idea is to connect the coils (with the known inductance) in series and in parallel and measure their total inductance. And you will be surprised how accurate this L-meter is.

17.44.2 Addition, or a simple explanation of why this works (link).
17.44.3 Addition, or what you need to know if you work with coils (link).

As usual, the page is not done yet.

17.04.2017  SKootS


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