Found this LC meter using the internal 16F628 comparators

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blueroomelectronics

Well-Known Member
Well for anyone following an old thread here's someone who actually did the classic PIC LC meter using the internal comparators on a 16F628
**broken link removed**
**broken link removed**
 
Thanks Bill, for the link to new version and definitely admire VK3BHR for the ingenuinity unlimited.. WOW!!
 
Nice find Bill.

I haven't been back to visit that site in some time so it's a nice surprise to find Mr. Rice has updated it with a single-chip LC Meter solution, something that you and I have been interested in for awhile now...
 
BIll,
I am going to play lazy and ask instead of looking.

How does this compare to the LC method/circuit used on the mondo superprobe?
 
The Mondo superprobe has some neat features but its L/C is very primitive.

Using a larger PIC it would be possible to combine the features of both.

Would you rather use a seven segment display or LCD display?
 
3v0 said:
BIll,
I am going to play lazy and ask instead of looking.

How does this compare to the LC method/circuit used on the mondo superprobe?
Click to expand...
as per the spec superprobe,
"When an inductor is connected from the tip to the ground lead, and button #1 is pushed, its value is displayed. Values from 0.1 to 999.9 millihenries are displayed. "

it can resolve .1mH

while the other one under concern can measure 10nH minimum-- while the original design of AADE.com can resolve .1nH
 
I would rather see an LCD with 15 or 20 characters.

It would allow real text instead of cryptic 7 segment labels

Also you could display Hz KHz and MHz instead of: no decimal for Hz, flashing decimal for KHz, and solid decimal for MHz. Or maybe it was flashing for MHz...

The processor would not have to mux the display.
 
I'm engaged in building this LC meter.....

But the 5V reed relay which is a low current type <30mA is nt easily available here...I think I've to get it from farnell india..........

But I think a 2N7000 moisfet can be used for the switching...can somebody tell me how to connect it....
 

hi,
You could use the pin that drives the reed coil to drive a 2N7000 gate and connect a standard relay in the drain circuit.
 
theo92 said:
But I think a 2N7000 moisfet can be used for the switching...can somebody tell me how to connect it....
Click to expand...

According to the FAQs by the designer, a 2N7000 mosfet can be used to switch the 1000PF capacitor. Here how it is connected:
 

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I have in my hand the same meter (more or less). Mine is old and I see there is a new version now. I also have a very big $$$ HP LCR meter that I do not use because this little meter is as good in most cases. It really works well at 1pF or to measure the inductance of 3" of wire. This meter will not work with BIG ele. capacitors.
Almost All Digital Electronics
 
eblc1388 said:
According to the FAQs by the designer, a 2N7000 mosfet can be used to switch the 1000PF capacitor. Here how it is connected:
Click to expand...

Nice info and thanks eblc1388, but it did not yield proper result when i tried last week. After this info, I would like to give another trial.


@ericgibbs
We could use even a BC547 for relay drive. with a base current limiting resistor.
 

It serves RF hobbyists well.
 
Can this be built using the PIC16F628A (note the 'A') without modification, also what tollerence do the components need to be?

This would be good to build into my multi-purpose workshop tool im working on (basically just relays/signal gen and freq counter)

I have a few boxes of unmarked caps - so it would be nice to know what they are!
 

It seems to be the math, the LC tank still oscillates just fine with monster inductors but the calculations are out of range.

Would be fun to try a dsPIC on the design, it's overkill but the math should be much easier to implement. Plus it should be easy to code in some additional features like a simple function generator etc...
 
Mine shows overrange after calibration screen.......can you find some possible causes::

and, my poor meter have a 450uH inductor in place of 82~100uH....which simply can't generate the expected tank oscillation frequency.....will changing it blow the overrange error away?

I've no 5V relay...but i'm looking about to buy a such from farnell.in .....I've connected a 2N7000 as me friend eblc showed...i think it's corrcet...
 

450uH is far too high perhaps. 100uH &5V relay are generally available.
There are single line and DIP relays made by either OEN or PLA. One can retrieve a relay from any dial up modem cards. we may use a drive transistor and directly use 12V instead of 5V regulated by 78L05.

perhaps , no need to resort to Farnel.in
 
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