Help needed desperately with PIC LCF meter

bigal_scorpio · May 31, 2008

ericgibbs said:
Hi Al,
I have built the LCF meter, on the bench, used the last 16F628A program in a PIC.
As I explained earlier the frequency of the CAP osc can be very high at switch ON.

This high freq is connected from the 4011 pin10 to the PIC pin 12 via a 10k resistor.
The high freq at the PIC pin after its passed thru the 10K is insufficient to switch the Tmr1 input,
so the program waits forever.!

Reduce the 10K0 [R5] to 4K7 [ put another 10K in parallel if its easier]

This fixes the problem 100% on my test set up ...

Can you give it a try, leave the test prods open as per the designers instructions.
Let me know what you find..

I know that the 10K is there to protect the 4011 output when an external freq is input,
but the 4K7 should get the same result.

Hi Eric,

You've done it again, may have to start calling you sherlock!

The resistor fix makes my meter work without locking with either Pic in!

Maybe now Bob can build his meter.

All the best............Al

mrx23 · Jun 3, 2008

Great work Eric!

I will definitely start building the meter

And one more thing. Is it possible to divide the incoming Ext. Freq. source by 2 (or more) with HW. And then give a gain of 2 (or more) in SW (just for the Ext. Freq subroutine)?
So it will able to measure freq up to 10Mhz (maybe 20Mhz) instead of 5Mhz.

What would you recommends for isolating the external signal at this frequency. It would be great to measure +- signals (like freq. generator's).

Thnx!
Bob

ericgibbs · Jun 3, 2008

mrx23 said:
Great work Eric!

I will definitely start building the meter

And one more thing. Is it possible to divide the incoming Ext. Freq. source by 2 (or more) with HW. And then give a gain of 2 (or more) in SW (just for the Ext. Freq subroutine)?
So it will able to measure freq up to 10Mhz (maybe 20Mhz) instead of 5Mhz.

What would you recommends for isolating the external signal at this frequency. It would be great to measure +- signals (like freq. generator's).

Thnx!
Bob

Hi Bob,
If I was going to use a predivider for the external freq input I would chose 'divide by 10'.
In that way it would be easier to read the displayed value...
At the higher freq you are not going to get the higher accuracy, so div by 10 makes more sense to me.
Also the PIC could handle the divided freq.

If you want to measure standard TTL logic levels the HCT or F series of divide by 10 would be OK.

For lower level signals a wide band preamp before the divider would be OK.

Does this help.?

mrx23 · Jun 3, 2008

Here is a cool Freq meter up to 50Mhz with the old 16F84.
We could use the input stage (or a simpler one).
A Low-Cost 50MHz Frequency Meter

LCF meter can measure 5Mhz TTL signal accurately.
So the final precision will depend on the preprocessing of the input signal.

I would like to measure sine/triangle/square signals from the Signal generator (and other sources). The signals are about +-2V range.
So we have to make it half wave (GND to +2V), buffer (or amplify), feed into Schmitt trigger, and divide the TTL output as much as we want, then feed the PIC with it.

Does this LCF support auto-ranging function? (Hz,Khz,Mhz)

mvs sarma · Jun 3, 2008

mrx23 said:
Here is a cool Freq meter up to 50Mhz with the old 16F84.
We could use the input stage (or a simpler one).
A Low-Cost 50MHz Frequency Meter

LCF meter can measure 5Mhz TTL signal accurately.
So the final precision will depend on the preprocessing of the input signal.

I would like to measure sine/triangle/square signals from the Signal generator (and other sources). The signals are about +-2V range.
So we have to make it half wave (GND to +2V), buffer (or amplify), feed into Schmitt trigger, and divide the TTL output as much as we want, then feed the PIC with it.

Does this LCF support auto-ranging function? (Hz, KHz, MHz)

It would be very difficult to procure chips like MC10116 (ECL types). thus it is preferable not to venture.

It is just a frequency meter. if such meter is needed with 9 level offsets as some HAMs use , One may find at www.hamradio.in and it used 16F628 , an improved version over 16F84 replacement for F84. I have a working version of this design.

Also I made a counter using the design by Fransesco Morgantini (ik3oil) and it works fine. Thanks to Morgantini.

ericgibbs · Jun 3, 2008

mrx23 said:
Here is a cool Freq meter up to 50Mhz with the old 16F84.
We could use the input stage (or a simpler one).
A Low-Cost 50MHz Frequency Meter

LCF meter can measure 5Mhz TTL signal accurately.
So the final precision will depend on the preprocessing of the input signal.

I would like to measure sine/triangle/square signals from the Signal generator (and other sources). The signals are about +-2V range.
So we have to make it half wave (GND to +2V), buffer (or amplify), feed into Schmitt trigger, and divide the TTL output as much as we want, then feed the PIC with it.

Does this LCF support auto-ranging function? (Hz,Khz,Mhz)

Hi Bob,
You should decide whether you want a simple LCF meter or a good quality freq counter.

I would suggest you build both units, look at Sarma's link.

mrx23 · Jun 4, 2008

Ok, 5Mhz will be fine. But the bipolar input would be very great.
Is this can achieved with the anti-parallel diodes?
**broken link removed**

We will need an external Schmitt Trigger, because there is an another signal source on the RB6.

What Schmitt Trigger should I use, and what will be the trigger voltage?

ericgibbs · Jun 4, 2008

mrx23 said:
Ok, 5Mhz will be fine. But the bipolar input would be very great.
Is this can achieved with the anti-parallel diodes?
**broken link removed**

We will need an external Schmitt Trigger, because there is an another signal source on the RB6.

What Schmitt Trigger should I use, and what will be the trigger voltage?
This will depend upon the input range.
Look at a comparator on the input stage, this will work down to 10's mVolt signal inputs.

[/QUOTE]

On the drawing you have posted, the input is 'ac' coupled, the diodes are used to clamp the voltage input at the base to +/-0.7V.
If the RB6 is on the LCF meter, the output from the 4011 to RB6 is via a 10K[ should be a 4K7], this is used to protect the 4011 from the ext freq input.

Kryten · Jun 19, 2008

Is it possible to extend it to measure frequenz as well without much alterations (I see that there are a couple of poles free on the rotary swithc).

I know threr will be a som mods to both the schematic as well as the software, but has anyone thought about doing so?
Im thinking about the PIC LCF meter that the thread is about

ericgibbs · Jun 19, 2008

Kryten said:
Is it possible to extend it to measure frequenz as well without much alterations (I see that there are a couple of poles free on the rotary swithc).

I know threr will be a som mods to both the schematic as well as the software, but has anyone thought about doing so?
Im thinking about the PIC LCF meter that the thread is about

hi,
It already can measure and display a frequency, use the 'ext' input.

tariq7868 · Jun 15, 2009

bigal_scorpio said:
Hi mrx23,

Just progged a 628 (notA) and swapped it into the meter and you were right in the assumption of the timeout being caused by the subtle differences between the 628 and 628A.

Now there is no timeout, the setup loop and even the null loop seems faster too.

As for testing caps, my strip of 100n tested from 97.75 to 101.5 the strip of 10n tested at 9.765 to 10.3 and the 1ns tested 0.98 to 1.020.

I also tested some 22ps and they were all between 21 and 22.2.

Pretty good as far as I can see, I am highly satisfied and now with no timeouts its even better Everyone should have one!

I still think someone should have a go at designing an ESR meter though, they may have been mainly used in a professional capacity (pun intended) at one time but as with most other things when they become cheap enough and readily available then they are adopted by a greater number of the average persons in the street, otherwise we'd still be lighting candles and I'de be chiselling this into a piece of stone in a cave hehehehe.

So if anyone fancies a challenge!

All the best.........Al

HI bigal_scorpio,
i m thinking of building the lcf meter from the epe mag of feb 2004 .. but i came to know there was some error in measuring the some capacitances and i have got here the circuit diag of it ,, so can u plz tell me whether u used the same circuit in the pdf i have attached.????

ericgibbs · Jun 15, 2009

tariq7868 said:
HI bigal_scorpio,
i m thinking of building the lcf meter from the epe mag of feb 2004 .. but i came to know there was some error in measuring the some capacitances and i have got here the circuit diag of it ,, so can u plz tell me whether u used the same circuit in the pdf i have attached.????

hi,
While Al is offline, I will answer, it is the circuit that he built.

What is the error regarding capacitance measurement.?

blueroomelectronics · Jun 15, 2009

There are simpler and better LC meter designs based on the 16F628A
**broken link removed**
**broken link removed**

tariq7868 · Jun 15, 2009

it was just that i happened to see some guys saying 'i noticed unexpected spurious oscillations in capacitor mode' & 'i cant have precision in nf scale, the capacitances of for example 10 nf became 4.7 nf' ... so thats why i thought of confirming...
One more thing :: i (too) cant seem to find 3.2768Mzh so can i use 3.5 or 4Mhz ?

blueroomelectronics · Jun 15, 2009

If you change the crystal you'll have to rewrite the source code.

tariq7868 · Jun 17, 2009

ok.i got it.thnx

tariq7868 · Jul 9, 2009

Hello.. i m also trying to build lcf meter using 16f628A but i cant download the above attached file (something wrong with the link) so can anybody plz again attach the hex file ??? thanks

ericgibbs · Jul 10, 2009

tariq7868 said:
Hello.. i m also trying to build lcf meter using 16f628A but i cant download the above attached file (something wrong with the link) so can anybody plz again attach the hex file ??? thanks

hi,
Ive rezipped all the program files.

tariq7868 · Jul 10, 2009

thnx a lot

tariq7868 · Jul 14, 2009

i hav made the pic lcf meter using 16f628A, but when i turned on the meter,only one line of rectangular boxes is appearing on lcd (i.e noting changed) & nothing happening.. i have checked all the connection which are alright..
i have a doubt abt my 3.2768 crystal, which was not available and i found it by chance. the value on the crystal is written as : ECS v 3.27 - 17 ,,, ..what do u think ???

Help needed desperately with PIC LCF meter

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