Converting/Inverting Analog Sensor Output From 5V-0V to 0V-5V

Thread Starter

mohala

Joined Nov 30, 2017
14
Hello,

I've been trying to wrap my brain on how to convert an output signal from a Vacuum Sensor
The Sensor is an NXP MPXV6115V -115 to 0 kPa.
The issue is that I want to connect it to a TI LM3914 (which allows up to 5V signal), to create a 10 LED meter

When the Sensor is at 0kPa the output voltage is approximately 4.5V. On the LM3914 that would consider it a high signal and so all LEDs would turn on.
I would want to have 0kPa as 1 or no LEDs and -115kPa as all LED to turn on and have the LEDs turn on progressively as the pressure builds.

I have tried and attempted with op-amp to invert the voltage which I get a nice Opposite voltage (e.g 5V gives me -5V, 4V gives me -4V and so on) but its not the 5V-0V to 0V-5V I wanted.

I was thinking is there a way to add onto the inverted op-amp voltage? so that when I get my -5V a circuit can be implemented to add +5V onto the inverted signal to get the signal I wanted?

Or is there just a simpler way (without an MCU) or circuit to do it?

I hope to hear from you soon.

Best Mo
 

Thread Starter

mohala

Joined Nov 30, 2017
14
Hello,

Thank you for the response, I originally was simulating on Multisim using a TL082CD two channel chip.

I ran the layout of the calculator on Multisim and the results came out odd, have I done it correctly?

upload_2018-8-28_13-43-59.png

I have attached the screenshot hopefully it shows.

It seems the output doesn't come out as expected.



Mo
 

Thread Starter

mohala

Joined Nov 30, 2017
14
Hello,

I reran another simulation with the same chip, this time I seem to have gotten somewhere except when the Input is at 5V the Signal line (blue) won't go any closer to 0V.

Any ideas to tweak the circuit? Would be much appreciated.
upload_2018-8-28_13-51-22.png

Best

Mo
 

ericgibbs

Joined Jan 29, 2010
13,650
Usually when someone submits a circuit as a solution they demonstrate and explain how the circuit will work.
I try to keep an open mind, but I do not see how this circuit will convert a Sensors linear analog 5v thru 0V signal to an linear output signal of 0v thru +5v.?

Inverting amplifier.gif
 

ebp

Joined Feb 8, 2018
2,332
"... but I do not see how this circuit will convert a Sensors linear analog 5v thru 0V ..."

It won't. It's essentially a switch. The linear range is small and variable from transistor to transistor and with temperature. It is completely useless for the requirement.
 

ericgibbs

Joined Jan 29, 2010
13,650
hi ebp,
I am puzzled why you have quoted me.?
I know it will never work as required by the TS.

Eric
BTW: that circuit was posted from post #12 link.
 

ebp

Joined Feb 8, 2018
2,332
Eric, I just quoted you as a means of linking my remark to yours and add my two bits worth that the circuit is useless for purpose, as you say.

I rarely use "reply" because it results in unnecessary repetition of something usually nearby. I prefer to quote just enough to establish linking for the bit to which I'm referring. I assumed it was the circuit from #12, though I normally will not go to sites like that to avoid being "harvested."
 

danadak

Joined Mar 10, 2018
4,057
ScottWang pointed out your power polarity for the negative rail of OpAmp
is wrong, hopefully in your sim you have fixed this.

Regards, Dana.
 
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