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

[Switch_639]

Re: V-F Converter cct

the LM331 pin4 is connected to GND... the LF411 pin4 is connected to -VS as stated in cct... I can measure supply voltages yes at pin8 of LM and pin7 of LF... they are at VS... all in use remainder pins also give me voltage... I think I am gonna build this frequency counter cct also... at least I can use a function generator to test the counter cct and if that works I can apply the other cct to it...

this is the counter cct... I wont use the regulator cct, no need as I have PSU... the MK1 and MK2 are just different options...

https://i531.photobucket.com/albums/dd351/Switch_639/FrequencyCounter.jpg

 

[karesz]

V-F Converter cct

... I can measure supply voltages yes at pin8 of LM and pin7 of LF... they are at VS...

And of course at -Vs/pin4 of LF too?
Apropos; what are your voltages pls?

... at least I can use a function generator to test the counter cct and if that works I can apply the other cct to it...
this is the counter cct... I wont use the regulator cct, no need as I have PSU... the MK1 and MK2 are just different options...

As you wish, but I mean: its better to make it to and, you are yet "in Knowlidge" of
your experiments, in next time maybe no more...
The countert to test with a generator is so + so good idea, but fish pls. your problem circuit too...
K.

Added after 1 minutes:

Maybe is good to check it as transistor is not on circuit...
What are Ube &Ue pls?

 

[Switch_639]

Re: V-F Converter cct

VS = 15V
Vin = 5V
Vb = 0.53V
Ve = 0.27V

the LF Pins
1. -15V
2. 13.73V
3. 0
4. -15V
5. -15V
6. -13.45V
7. 15V
8. 0

LM Pins
1. 13.72V
2. 1.91V
3. 5V
4. 0
5. 15V
6. 0.34V
7. -1.05V
8. 15V

dont know if this helps...

 

[karesz]

V-F Converter cct

Hi & sorry, I didnt see your data...
Can you measure pls the ohmic resistance on pin3 of LF?
1,
Hier is some thing wrong, then an OP has on both inputs similar potentials to have (exactly is real a small difference present, called offset voltage), I think your 1nF capacitor, or pin3 self, is maybe shorted to GND, otherside is LF dead?
",
Your U/F converter is pls WITH MINUS voltages TO CONTROL!!
Is the 1N4002 diode with Cathode (Marking ring) on the LF-output_pin6_?

You can make a change at Uin: short it/or solder it pls to GND & repeat the same measurements.
Respectively as 3. version: apply pls. -5V to the Uin and repeat the measurements!!

So much on the speed...
K.

 

[Switch_639]

Re: V-F Converter cct

maybe will take a while but I will do it and get back to you... maybe im gona replace both LM and LF and also the transistor, cause they can be main issues... the other components im sure will be good...

 

[Switch_639]

Re: V-F Converter cct

here are my values again... I rebuilt the cct and used 15V for supply and -5V for input voltage... the ohmic resistance on pin3 of the LF was = 1 ohm...
Vb = 1.47V, Ve = 0.94V

LM pins
1. its like its oscillating, going up and down between certain voltage
2. 1.61
3. 5
4. GND
5. 0.099
6. 7.46
7. 0.734
8. 14.9

LF pins
1. -14.74
2. its like its oscillating, going up and down between certain voltage
3. close to zero
4. -15
5. -14.8
6. 0.75
7. 14.9
8. -

 

[karesz]

V-F Converter cct

Hi_fein!
Only 2 speedy questions:
1,
I think, the 1N4002 is in wrong direction on LF/pin6.
You have her 0.6-0-7V, that is = a diode in forwarded biasing...You wrote +0.7V for pin6, diode is on and I think you need it other?
In all case you must on this point Cathode have, then with +Uoutput voltages is a cathode reverse biased, can not be a potential to measure at 0.7V at the point/pin!
2,
You have/measure yet on LF/pin3 to GND the same ca. 1 Ohm?
Then take the 1nF pls off/out (for test) & repeat your resistance measurement!

If LF/pin3 is no more at GND (1Ohm=pin3 is shorted to GND) your circuit must begin function; LM/pin3 will be no more at 5V(can you see it on an oscilloscope as pulsed or is a stabil DC on it?), it will be somehow pulsed...
K.

 

[Switch_639]

Re: V-F Converter cct

maybe that cap is causing the problems... gonna take it out and check what happens...

Added after 12 minutes:

you were right also about the diode! i had it the wrong way around... so stupid... and I have also takin out the cap on pin3... will check it on oscilloscope later and get back... thanks!

 

[karesz]

Re: V-F Converter cct

... you were right also about the diode! i had it the wrong way around... so stupid...thanks!

Aha! And I asked you par scripts ego more times over your diode & OpAmp +/_ pin equivalent /possibility(as problem...
Good luck for full function_waiting for reply...
K.

 

[Switch_639]

Re: V-F Converter cct

ok, its still not functioning properly... here are results... also LF pin3 voltage I can change with the pot... what voltage should there be? is that not the offset voltage? cause I have adjusted it close to 0V... I am getting some sort of wave on the output... but it looks like AC sino wave so it cant be correct, also the frequency doesnt change if I increase the Vin... so its not correct...

LM pins
1. alternating
2. 1.42
3. 5, also I set this by using the voltage logic resistor
4. GND
5. 0.115
6. 7.4
7. alternating
8. 14.9

LF pins
1. -14.74
2. alternating
3. close to zero, this I adjust with the pot
4. -15
5. -14.8
6. alternating
7. 14.9
8. -

 

[karesz]

V-F Converter cct

OK,
yet is pin 7 alternating; is this (some triangel form) signal at 7.5V? (+/_ some peak-peak)
If it so is: you check hier (with your scope pls) amplitude/excursions over pin6-Threshold 7.5V>> you will/must have pulses on output pulldown/LMs pin3...
Yet you need minimum an scope, + a counter will be good too.
if it pulses on LM/pin3: as I wrote early, set minus 10V on Input and try justage to 100KHz trough "fullscale" trimmerr, after them put 0V (or short) to input & setthe offset voltage Difference between OP pins 2&3 to null(means really ZERO!!/less cuple of mVs)_measure the output Frequency (I think it is not zero, but low).
repeatedly check at fullscale the Fout.
What about sweeped minus input voltage/0 to minus 10V?
If it is not in full function: check pls component values, put in new capacitors...
"alternating signal" at pin7 must swing around 7.5V/threshold> this is requirement for output signals!...

 

[Switch_639]

Re: V-F Converter cct

Pin7 of LM and Pin6 are now at 4V... I have Vsupply at 10V... Vin was -5V... offset is 0V... none of the pins are alternating... I changed nothing... just tried again this morning... and this is what happens...

 

[karesz]

V-F Converter cct

Hi,
Of course have you changed some thing; i.e. the supply voltages!!
You have yet 10V, but you have had +/- 15V!
This is the reason for 4V on pin6 of LM_it is at 50% of Usupply, but read pls nationals datasheet-version, as I wrote for you more times: this is better detailed!
You can not change "randomly" Usupply, then you have an analog system, some currents/workings points are created of varied voltages_to end it must be not functionell...

Make the same situtation as half day befor pls_I think +/-15V_& repeat your measurements...
k.

 

[Switch_639]

Re: V-F Converter cct

what should I look for on the National pdf file of the LM? I really don't know what I am looking for or should be looking for... you think 15V would be the min then? it says I think as low as 5V... what is the prob maybe?

 

[karesz]

V-F Converter cct

Look, you have had a Usupply=15V befor, to that are your measurement values.
Yet is your Usupply garanted no more 15V, more at 10V ore some less, then your 7.4V is yet at 4V...
If you read the daatsheet, it is to find, that the double star resistors/some components have a value for Usupply over 8V and other as it is less .
OK, You can apply 5V too, but than you must not tell; I have nothing changed, but the voltages are others_sorry:-(

You MUST take pls such Usupply values and fix it, for your tests,debuging & repeat your measurements on all pins wit the fixed voltages,.
I wished only these sentence to write you in the post over these...
K.

 

[Switch_639]

Re: V-F Converter cct

https://i531.photobucket.com/albums/dd351/Switch_639/osc.jpg

ok I will change back to 15V as at least I could see some wave looking like this... but very distorted, not as nice as this one... I would really need a counter cct I think to get this accurate... as I applied less or more input voltage to the cct the frequency didn't seem to change on oscilloscope... you think the cct is close enough to get functionality?

 

[karesz]

V-F Converter cct


Pls, you can drive it (if you wish it )with other supplies, but fix it for the tests!!
OK, if you have 15V and similar pulses at LMs output_you can check the time scala/signal frequency, you must not have a counter at this time, then _ I think you have suh other problems to repair as "job to do first"....
Check it exact pls; if you apply Negative Input control from 0V up to -10V, what will change.
K.

 

[Switch_639]

Re: V-F Converter cct

ok great... I know you have told me this and getting frustrated but bear with me... I have changed to positive 5V for Vin... now there is oscillations on pins... there is also on pin3 of the LM... now tell me why do I need to supply it with 5V also via that resistor of 10K value (the pull-up resistor) ? will my frequency pulses be at 5V peak? or what is the reason there?

 

[karesz]

V-F Converter cct

You see, if your next board is supplyed with 5V, you have logic sytem with 5V(similar as TTL) _ you must have signals into these PCB between 0 and 5Vpp, but minimum over cca 2.1.....2.5Vpp=2.1--2.5V is standard minimal TTL input High-level.
You can put the pull-up at LMspin3 to5V upto Vs, in thes case =+15V.
Your output pulse has regularly an (peak-peak)amplitude between Vsupply of Rpull-Up and GND(=0V)
If your next board(counter) is TTL compatible, works at 5V, put the output pin 3 (of course trough the pull-up of 10Kohm!) to+5V!!
Than you must have at these LM pin3 pulses between 0 and +5Vpp, minimum over 2.5v!
If your "0" is = +4...5V as in your tests, & LM is not defect = you have not 10Kohm pull-up at pin3!! or your load is not OK(to much current is sinking from your LM-output, the transistors saturating voltage rise up to 3...4...or even 5V if your load current is i.e. at 50mA!!
YOU HAVE SOME THING WRONG HERE...Maybe is your pull-up c lear smaller as 10KOhm!?
Your LM331 is specified for only 5mA(typical 3.2mA9 at Uout "0" = max 0.5V!! _ not 5V...Datasheet, pp3.
Check pp5, over Nr5 direct: "Output saturation Voltage versus Iout"...

You need external pull-up to supply the output amplifier of LM331, their collector is direct connected to pin3, has no resistor on chip!..
Trough these designer phylisophy is the IC more flexible_ you can set some working point for you...
K

 

[Switch_639]

Re: V-F Converter cct

my pin3 of the LM is pulsing 0.25V then 0.28V and so on... its alternating like that... is this ok? this is measuring from pin3 to GND...

Added after 1 hours 2 minutes:

https://i531.photobucket.com/albums/dd351/Switch_639/SDC12444.jpg

this is the reading I get from the osc... is it not suppose to be square wave?