voltage to Freq converter

[snooze]

Hi i need a VTF to convert voltage to Frequency for some testing.

I'm using VFC32

https://www.electro-tech-online.com/custompdfs/2011/05/0900766b800ac2d1.pdf

Problem: I have wired exactly the same as the figure 1 but can't get the circuit working.

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troubleshooting:
1. without any passive component, connect power supply +/-15V, connect Fo to oscilloscope. sinewave of 15Vpp show on scope
2. connect exactly same circuit recommended, weird waveform. not squarewave


PLease help.... Thanks in advance

 

[BrownOut]

1) Is probably niose because you haven't connected anything to the input, leaving it open to collect any niose in your environment.
2) Need more detail.

 

[snooze]

1) Is probably niose because you haven't connected anything to the input, leaving it open to collect any niose in your environment.
2) Need more detail.

1. ok, noise.
2. after i hook up all components, the waveform is distorted. and increasing the Vin from 0V to 10V doesn't change the output waveform (voltage and freq)
3. removing the pull-up resistor, I am still seeing the same distorted waveform..

 

[BrownOut]

Can you look at Vin and Vout ( or Vint, can't really see how it's labled ) and compare them with the graphic on your schematic?

PS, how are you connecting the grounds?

 

[snooze]

Vint (Vintegral).. i tried comparing the o/p against the graphic on schematic and it is not the same...

 

[BrownOut]

Not very descriptive. You need to put in more effort and tell us what you're seeing. Otherwise, good luck with that.

 

[snooze]

Can you look at Vin and Vout ( or Vint, can't really see how it's labled ) and compare them with the graphic on your schematic?

PS, how are you connecting the grounds?

tied all ground (common) to the +/- 15V power supply. such as c1, VFC32 pin 11, op amp +ve terminal


will get a print out of the waveform.

 

[snooze]

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this is what i see at the pin 7 Fout

definitely not the same figure in the schematics

 

[BrownOut]

tied all ground (common) to the +/- 15V power supply. such as c1, VFC32 pin 11, op amp +ve terminal

Where? That tells me almost nothing.

this is what i see at the pin 7 Fout

That's 50 Hz noise. Under what conditions do you measure this? How is the chip connected? Is this the measurement with no passives? What about the measurement of VINT? I can't help much with what you're giving me.

 

[snooze]

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this is the point i tap to check the waveform after the op amp at pin 13 Vout

Thanks in advance..

this is the Vint.. suppose to be sawtooth but it just swing / saturated to max..

 

[snooze]

Where? That tells me almost nothing.



That's 50 Hz noise. Under what conditions do you measure this? How is the chip connected? Is this the measurement with no passives? What about the measurement of VINT? I can't help much with what you're giving me.

pin 14, 11, C1 all tied to the +/-15V common terminal of the power supply. will draw all and post pic soon.



measurement is with all passives connected. wire to figure 1 in 1st post.


Vint figure is below.

 

[BrownOut]

this is the Vint.. suppose to be sawtooth but it just swing / saturated to max..

that's more 50 Hz noise. You either have a blown chip, or it's not connect correctly.

 

[snooze]

OIC. ya the waveform is 20ms or 50Hz.. Thanks

now i dunno where i connect wrongly.. shall i draw out single line diagram to illustrate how it is wired up?

 

[BrownOut]

Do you have an actual input? Or have you left pin 1 unconnected? I don't need to see a diagram, you only need to confirm you are connected exactly as the schematic and have an input voltage. I suspect there is an unconnected input. Other than that, I don't know what else could be wrong.

 

[snooze]

yes the pin 1 is connected to 40Kohms. a DC +ve voltage is connected to the resistor in series, -ve voltage is tied to common of IC pin 11


i shall draw equipment and wiring of the circuit tonight.. for a better picture..

 

[BrownOut]

-ve should not be connected to common. It should only be connected to the -vcc pin.

 

[snooze]

-ve should not be connected to common. It should only be connected to the -vcc pin.

OIC. will correct it the next working day. Thanks for your advice.

 

[snooze]

btw, where does all the common ground tied to?

 

[snooze]

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[snooze]

Hi is my connection corresponds to the schematics