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Help me fix some problems in a V-F converter circuit

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V-F Converter cct

`evening,
1,
Also, this is "not so direct a square":-(...
Then, you must have at these pin3 a full "logic range"=0 .. +2.5V optimally at 5Vpp_ if you have the pull-up on +5V.
2,
the small excursion(& waveform) demonstrate us, that possibly is your pull-up not direct worked on pin3!
Looks like a GND disturbance only, or was your probe not right/correct installed (is the tip correct pressed onto?)?...
Pls check your probes with the scopes calibration signal_or with some other knowed amplitude square wave!

Pls measure your pull-ups value(resistance) direct from pin3 to Vcc (between LM pin3 and logic supply), but with switched down circuit!!

I belief: you dont have a real 10 (or such)Kohm between the both points.
What is time scale from these photo?
Did you an GND line by your probe tip clipsed to GND? If not_pls do it, it will give a better square form_ but the amplitude is in all cases wrong!
K.
 

Re: V-F Converter cct

do you think at least its close to starting to work properly? think I should change the IC's and transistor? or is this not the problem? I will build that counter circuit also and see if I can vary the frequency with Vin... if the problem is mainly probes and stuff, if you think so then I don't care... if the amplitude is wrong, what could be the problem? ok so I checked that 10K resistor on pin3, its 9.88K... I also checked the voltage on that resistor, its 5V from the extra supply I use... if I measure from pin4 (GND) to pin3 it varies 0.25-0.28... jumps like that...
 

V-F Converter cct

Hi,
you can check your probes with the "calibrating signal" from your oscilloscope_I think you have so an output on that? Do it pls, as I wrote some earlyer.
The 10 KOhm: measure it pls direct from IC pin Nr3 with a fine tip! Can be that its not contacted to the IC _LM/pin3...
If both jobs indicate negative, you must change LM331...
For testing your counter -you must know how good functions your scope/probe system.
K.
 

Re: V-F Converter cct

I replaced both the LM and LF in the circuit... I get the same kind of output pulse... its not square wave... I built a pulse counter cct to test the pulses coming from the converter... the counter works, tested it with function generator... but the frequency converter pulses do not work on the counter... what other ideas could you have in getting the converter to work?
 

Re: V-F Converter cct

Switch_639 said:
... but the frequency converter pulses do not work on the counter... what other ideas could you have in getting the converter to work?
Click to expand...
Hi,
to first_ congratulations for your counter success!:))
Yet is only to repeat that with the V/F conversion too...

To second,
Your counter will never work with these (micro amplitude) ca. 200mVpp output signal of UF-onverter!!
The counter has CMOS Input, means High Level MUST BE OVER (internal) Uref( min. 2.1V) , typically over 2.5 Vpp)!

Maximal works is if you will apply AC-coupling, but these isnt the clear soluting of your LM331 problematics...

I wrote it for you some earlyer, that the UF-conv doesnt right work:-(
I dont have yet some Idea what are you doing incorrect, but the thing is wrong in function...
My proposel was too, tat pls build a simpler version to check your realysing, but you didnt wish it to do...
Good luck!
K.
 

Re: V-F Converter cct

I have decided to take your advice and try the simpler circuit and try to get it to work first... then for a frequency counter... what can I use that would accept those small signals and display them on my counter... you said the counter I was using would never work which you are correct about... you have another cct I can use to work with the LM331 output signal?
 

V-F Converter cct

Hi Switch_639,
you are writing on jan. 14.:
..."I built a pulse counter cct to test the pulses coming from the converter"...
Im yet suspect with your past posting over counter...Is it these from Jan.05:
https://i531.photobucket.com/albums/dd351/Switch_639/FrequencyCounter.jpg
I wrote only, that these will never work with so low level signal as ca. 200mVpp, becouse has CMOS logic level inputs= need min. 2.1-2.5V pulses...
Dont worry, denn i think your VFC will give these pulses - if properly works.:)
I would say a goog progress can be as follw (too), if Im right:
1,
you have your wished counter, that works _controlled w. external generator_GOOD.
2,
You will build a simpler version of VFC to check it out what was your systhematic failure: if it works, you will change it to your needed complexer version.
3,
I think; your project is finished if you yet will do connect your both moduls:)
K.
 


V-F Converter cct

You are welcome, try it pls!
As more simple to check out; you can have only a ca. 15 KOhm at pin2 & can forget the offset poti+22K&47Ohm too.:)
Insert a 100nF bettween +15V & GND pls_on all breadboard circuits is as bypassing needed.
K.
 

Re: V-F Converter cct

Switch_639 said:
will do but I only disregarded the 22K and poti...
Click to expand...
Clear, this isnt a problem:)..
 

Re: V-F Converter cct

I calculated with these values I can get 8.443 Khz output... by adjusting the rheostat to 14.2 ohm I can get fullscale 10K at 10V...
 

V-F Converter cct

:)
Fein, try it pls!
I belief, that the exact frenquencies arnt of interest, but more: does it functioning?...
Good luck!
K.
 

Re: V-F Converter cct

good news... it works perfect... 10V = 10Khz... but changed the 12K on pin2 to a 8.2K and then could I only adjust with the rheostat to get properly to 10Khz... before it was at 11Khz and rheostat at 0ohm... thanks for all this help... I couldn't get the 100Khz output cct to work but at least this one works fine...
 

V-F Converter cct

Hali!
Congratulations!:) Can you send some pictures too pls?
Check for possible differences between your both breadboards, if you have the old one too, it is good to learn from failiures!
Full range poti: I would not take out the fix resistor, maybe change it to some lower value, a i.e. at 3--5 KOhm...Do you have checked yet the offset controlling too?
k.
 

V-F Converter cct

Hi,
good, but i would see a pic over your pulsout pls_sorry I was not enough clear...
Do you like to built on these board your offset controlling too? As first "job":)
K.
PS:
You can built on the plus OP & after them it functions the transistor on these Board too?
In all case; maybe is better to take a new one & in multiphase built every time more complex? As you likes:)
 

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