Help needed desperately with PIC LCF meter - Page 5 - Electronic Circuits Projects Diagrams Free

bigal_scorpio · 31st May 2008, 07:07 PM

Quote:

Originally Posted by ericgibbs

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 · 3rd June 2008, 08:28 AM

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 · 3rd June 2008, 08:53 AM

Quote:

Originally Posted by mrx23

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 · 3rd June 2008, 11:03 AM

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 · 4th June 2008, 03:53 AM

Quote:

Originally Posted by mrx23

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 · 4th June 2008, 06:53 AM

Quote:

Originally Posted by mrx23

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 · 4th June 2008, 09:12 AM

Ok, 5Mhz will be fine. But the bipolar input would be very great.
Is this can achieved with the anti-parallel diodes?
http://www.hamradio.in/circuits/images/lcdcntr.gif

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 · 4th June 2008, 09:44 AM

[quote=mrx23;317124]Ok, 5Mhz will be fine. But the bipolar input would be very great.
Is this can achieved with the anti-parallel diodes?
http://www.hamradio.in/circuits/images/lcdcntr.gif

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 · 19th June 2008, 11:34 AM

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 · 19th June 2008, 12:22 PM

Quote:

Originally Posted by Kryten

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.

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3rd June 2008, 08:28 AM	(permalink)
mrx23	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

3rd June 2008, 11:03 AM	(permalink)
mrx23	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)

4th June 2008, 09:12 AM	(permalink)
mrx23	Ok, 5Mhz will be fine. But the bipolar input would be very great. Is this can achieved with the anti-parallel diodes? http://www.hamradio.in/circuits/images/lcdcntr.gif 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?

4th June 2008, 09:44 AM	(permalink)
ericgibbs	[quote=mrx23;317124]Ok, 5Mhz will be fine. But the bipolar input would be very great. Is this can achieved with the anti-parallel diodes? http://www.hamradio.in/circuits/images/lcdcntr.gif 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. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

19th June 2008, 11:34 AM	(permalink)
Kryten	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 __________________ Simplicity rules Good enought - its perfect ?? 2 Gig of free online backup space Are you a Chemist? Last edited by Kryten; 19th June 2008 at 11:35 AM.