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LC Meter using AVR microcontroller




LC Meter:

 Schematic Source code
This is the project I am currently working on (2010-01-23). The LC meter is based on Elmcie or Elsie and other similar LC meters. This project is in a very early prototype stage and is at the moment only capable of measuring inductors. Even though I have build the first prototype on a breadboard the results are very impressive. No problems with instability of the LC oscillator. Seems to measure the inductance of a small wire in the nH range. Just for fun I connected a power transformer and I measured an inductance in the range of 7H for the primary winding. I did some calculation based on the current consumption of the unloaded transformer and it seems to work out O.K. On the pictures I connected a big LCD (2×40) but that is just for debugging. The final meter will have a nice and small 1×16 display. The debug values on the top row of the display are: 57466: Accumulated value of Timer1. 19 is the amount of (20ms)interrupts it took to accumulate the Timer1 value. 151226 is the calculated frequency of the LC oscillator.

LC Meter

Just a little reminder to myself of what I want to make

  • Maybe use multiple calibration L’s or C’s to make it more accurate in some ranges.
  • Show negative values on te display to indicate the calibration is off.
  • Normally connected to the network, maybe also on a 9V battery (backlight off).
  • Extend it with frequency measurement, the 2nd half of the lm393 can be used as the input buffer.
  • Use a multiplexer (74C151) to switch between multiple frontends for the LC meter.
  • Mux can also be used to switch between a prescaler for the frequency measurement.
  • show only significant digits for all measurement ranges.
  • Use a bistable relay for switching between measuring L’s and C’s to save battery power.
  • Built in Ni-MH battery charger? (7.2V GP Recyko?)
  • Disable backlight when on battery power.
  • Use a 3.5mm audio plug for connecting measuring cables.
  • Other options for connecting cables: 4mm Banana / BNC / cinch / female 2p header.
  • Put connectors parallel / select switch / change plugs.
  • Use shielded microphone cable for measurement cables.
  • Make some kind of pincet for measuring SMD components.
  • Use 2x 1/2 ic socket for measuring components with small wire’s.
  • Use 2 single row female header for measuring components with thicker wires.
  • Make special connections for measuring SMD components (in different forms).
  • Direct push buttons for selecting the right function (Frequency, Capacitors, Inductors)
  • Maybe use a sliding switch for function selection.
  • Rotary switch gives easily up to 12 different measurement functions.
  • Also measure ACA / DCA / ACV / DCV / RMS / Averaging / Differential voltage / Resistors / diode test
  • Pushing the frequency button multiple times selects beteween: Frequency / Period, Positive time, Negative time, dutycycle,
  • Direct push button for zero calibration.
  • Pressing the zero button shortly zero’s
  • Last selected function is stored in EEPROM when turning the device off.
  • All calibration values are stored in EEPROM and read upon power up.
  • Add current source for diode / led test.

For more detail: LC Meter using AVR microcontroller

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