Please suggest a good Frequency and LC meter using AVR

[desai_amogh]

Hi,

Please suggest a circuit diagram with both LC and frequency meter combined.

requirement:

L: few uH to few Henries
C: few PF to few u Farads
F: Few Hz to at least 50 Mhz

I searched online but mostly found either LC or F meters. Did find one combinded F and LC meter based on AVR here: http://www.kerrywong.com/2010/10/16/avr-lc-meter-with-frequency-measurement/

but his one does not mention its range.

[Rerouter]

if your not too concerned with perfect accuracy (fractional Hz) you can use a clock divider and an AVR external interrupt to easily count Hz, (my little device on a 328p counts up-to 250Khz before the interrupts own overhead prevents the display update code from running,) , meaning you would only need a divide by 8 if you really wanted to push the limits,

as for capacitance and inductance, you have a few ways, one of the simpler being an LC oscillator, where one of the values is a known value and the other is added externally, you then measure the frequency and can determine the value of the other piece (this doesn't account for parasitics too well though, unless you calibrate it in software somehow)

other approaches might be to use the inductance and capacitance measuring chips that have started popping up, though i am not sure quite what there output signal is the inductance ones have been mentioned quite a bit and should be easy to find something on,

[dannyf]

AVR's counters are synchronous. So you have to use an external divider / prescaler - with that,  you can easily go to 100 - 200Mhz or even more, depending on your divider used.

You may want to design a way to read the divider if you want Hz level resolution.

[I_may_be_drunk_right_now]

That's a good observation, I'm a bit surprised at the lack of a combined, just-accurate-enough cheap&cheerful gizmo for those 3 measurements. A typical older DMM only does V,A,R diode measurements, so a F,L,C thingy would be a perfect complement.

If you can make one that works well, can be produced in lowish quantity cheaply (maybe by you) and is nice enough for everyone, you might have a few months of sales until the Chinese copies flood eBay.

[hli]

I can suggest the LCFEsr (http://members.upc.hu/lethanh.hung/LCFESRmero/en/). It does capacity and ESR, large and small inductors, and frequency up to 8MHz. As noted, with an AVR you need a prescaler, but these are easy to build.
I did build this up by myself, and am quite happy with it (so I went and bought the AVR with the non-demo software on it). Its not the simplest one, but reliable and accurate.

[kripton2035]

here an esrlcf meter with a pic and ... open source.
http://kripton2035.free.fr/LCR%20meters/esr-lcfmetermicr.html

another one with hex file, but no source code
http://kripton2035.free.fr/LCR%20meters/lcr-r2d2.html

[linux-works]

I started with kerry's idea.  there is a frequency counter library for the arduino and that is the key.  lm301 (iirc) as the oscillator and you just connect L or C or R at the right points, get the freq and do the math.

I started building one, here, in a small box, but never finished the code.  the hardware works great, though.











I used my own LCD display board (the LCDuino; you can buy them at amb.org as bare boards) which contains the arduino 328 chip, a port expander for lcd i/o, a real time clock chip (not that you need it here) and even a motor pot h-bridge (again, not needed here but used for other projects).  there is an adafruit 3v to 5v dc-dc upverter, an lm310 (again, I think that's what I used) which is the standard thing you see, such as in kerry's write-up, and even an xbee for remote programming (!) and remote data logging, if you are so inclined.

I may be able to find the firmware/src I used, but like I said, its unfinished and I'm not sure when I'll have time or interest to complete it.  getting the hardware done was most of what I wanted and after that, I kind of lost interest in completing it