Help needed desperately with PIC LCF meter

[lynx]

hi eric

hi lynx,
I assume that on your version of the LCF meter that you have the SET push button connected.? and that you carry out the Correction procedure as explained in the pdf.?

yes i did..

I have built the inductor osc section and it works OK, testing using a number of 4011 gave wide differences in the base frequency [ ie: when the test probes are shorted together]
The 10Kpot has a VERY wide range of frequency settings, I guess thats why the SET push button is used before measuring.

The base 4011's frequency outputs remain stable enough, over many tens of minutes.

mine can't remain stable.. :/

at you previous post you say it could be the PCB? how can the PCB cause such a problem? is it stray capacitance?...

 

[ericgibbs]

hi eric



yes i did..




mine can't remain stable.. :/

at you previous post you say it could be the PCB? how can the PCB cause such a problem? is it stray capacitance?...

hi,
The stray capacitance on the PCB should be fairly constant, how long are your test leads.??

As I recall you are not in the UK.??

 

[lynx]

the test leads are about 10cm long...

no i'm not in the UK, by the way i got a small oscilloscope...
and shorting the leads and measuring between the minus of the battery and the
pin 12 of the uC the frequency is around 20KHz and fluctuates a little bit up
and a little bit down

 

[ericgibbs]

the test leads are about 10cm long...

no i'm not in the UK, by the way i got a small oscilloscope...
and shorting the leads and measuring between the minus of the battery and the
pin 12 of the uC the frequency is around 20KHz and fluctuates a little bit up
and a little bit down

hi,
With the test leads shorted together, the frequency on pin 12 of the PIC should be about 300KHz, if its only 20KHz check that the inductor wired to the PCB is really 10microHenry.!

Also look at this image, , is that pin hole soldered in correctly.??
What are those long black wires fastened to the end of the R5 resistor.?
Its hard to see on your PCB images.

EDIT:
I cannot see the 'L1' 10uH inductor on the PCB, could you mark it for me.?

 

[lynx]

hi,
With the test leads shorted together, the frequency on pin 12 of the PIC should be about 300KHz, if its only 20KHz check that the inductor wired to the PCB is really 10microHenry.!

it's hard to tell right now because of HMA around the inductor..but as far as
i remember the value of the inductor is correct. turning the pot to the right the frequency
can go up to 500KHz turning it to the left goes close to 19KHz

Also look at this image, , is that pin hole soldered in correctly.??
What are those long black wires fastened to the end of the R5 resistor.?
Its hard to see on your PCB images.

yes it is fine, i don't know why it looks like it's not soldered...maybe it wasn't soldered
when i took the photo.

EDIT:
I cannot see the 'L1' 10uH inductor on the PCB, could you mark it for me.?

check the new photo...the inductor is near the R5.

 

[lynx]

Hi...

i was wondering... other than ericgbbs nobody else can contribute
with some knowledge?

after all this talk and and tests..i believe the problem with my LCF meter got norrowed down to
4011 gate, something is wrong with the oscillator..but what is wrong? can that be saturation of the
gate which makes the oscillator not that steady?!

i also want to add that when i tried to measure the inductance of a transformer
the results where steady, so i'm very confused with all this issue.

i appreciate ericsgbbs try to help me...also anybody else willing to give a farther help!

 

[ericgibbs]

Hi...
i also want to add that when i tried to measure the inductance of a transformer
the results where steady, so i'm very confused with all this issue.

If the project works OK on the transformer are you 100% sure that the project really has a problem.

Test a number of known value inductors and post what you measure.

 

[lynx]

the instrument is not calibrated very well, since the readings aren't steady
i can't calibrate it until i fix it.

please check this video i believe it is helpful enough so you can understand
the issue much better.

ImageShack® - Online Photo and Video Hosting


P.S can you please explain to me generaly what can cause such stability issues with oscillators built around a gate?

 

[ericgibbs]

hi,
Watched the vid.
The frequency of the oscillator is increasing with time [ which I guess you realise] this will give an apparent decrease in the inductor value.

Have you monitored accurately the supply voltage on pin #14 of the 4011, while you are taking a inductor measurement, lets know what you see.

EDIT:
What are you using to power the PCB. ???

 

[lynx]

hi

i'm using a 9V battery, i'll let you know for the rest later.

 

[ericgibbs]

hi

i'm using a 9V battery, i'll let you know for the rest later.

hi lynx,
I assume that you do have a 7805 Vreg between the project and the 9V battery.??, if you do have the 5Vreg, check the battery and the +5V..

Depending upon the battery type.?? it may not be 9v.

 

[lynx]

hi lynx,
I assume that you do have a 7805 Vreg between the project and the 9V battery.??, if you do have the 5Vreg, check the battery and the +5V..

Depending upon the battery type.?? it may not be 9v.

everything is exactly as in the schematic...the battery is a normal 6LR61
9V battery (a little bit empty but still holds)

at the pin #14 of the 4011 gate the voltage is 5.04V

 

[ericgibbs]

hi lynx,
Ref your PM's
I have relooked at the project pictures and only error I can see is the way the SET switch is connected.
All it does is link two pins #1 and #3 on the PIC.
Pin #1 is supposed to go to +5V via the SET switch and if you are only using the inductor section pin #3 is connected to +5V.

Let me know what you find.

 

[lynx]

eric you say i should cut the track and relocate the "S3" and let "S2c" nc?

 

[ericgibbs]

eric you say i should cut the track and relocate the "S3" and let "S2c" nc?

hi,
If you are not using the CAP mode, wire PIC pins #1 and #2 like this image.

 

[mvs sarma]

I fear, too long wires connecting to switch might cause problems of instability. Check if you can reduce the wiring to bare minimum.
Many other designs, in fact, recommend on board switch with suitable pcb artwork , let it be rotary or sliding.

 

[ericgibbs]

I fear, too long wires connecting to switch might cause problems of instability. Check if you can reduce the wiring to bare minimum.
Many other designs, in fact, recommend on board switch with suitable pcb artwork , let it be rotary or sliding.

hi Sarma,
lynx is making a 'cut down' version of the LCF meter, he only requires the Inductor test function.
So he has dropped off the Select switch, when doing this he has made a mistake of connecting PIC pins #1 and #3 together.

BTW: he did make the full version which did work.!

Eric.

 

[mvs sarma]

Thanks Eric. For Inductance meter, perhaps one design by Phil Rice of Australia is found to be best
it also works well for C . resolution appears Good. for the concerned issue i would join back shortly

PS: the values of C5a& b and C6 a&b are expected to be close tolerance such as 1%. This is one major cause for instability, once other things are attended to. See the component list of the article concerned. We had used such accurate caps buying from Farnell.Of course our design (phil Rice )used 1000pF 1%.


I doubt whether LYNX has them and used them.

 

[ericgibbs]

Hello everyone, I would like to build the LCF meter, but first I would to simulate it in Proteus Isis 7. It doesn`t display only 0Hz or Inductor Timing , using the code uploaded by bigal_scorpio for PIC16F628A . Could anyone help me please? I could try to send the project and lake a look at it . I`m an amateur and trying to learn electronics. Thank you

hi Paul,
Ref your PM, is this what you are asking for.??

 

[Ohmnium]

Hi. I'm trying to build the EPE LCF Meter, but the pic that i'm using is the 628A. I had problems to download the hex file which ericgibbs proposed. I probed some hex files from different forums, but any of them worked. In the mode of capacitor, the LCD display "Capacitor time out". Someone built the circuit an it worked fine?? What hex file used?? Please, I need help