Markley02

Which circuit is more complicated? Using the OP365 or the LM358. I tried searching for OP358 and I couldn't find a datasheet.

ericgibbs

hi,
Where did you get the OP358 type number from?

The circuit design is the same for the LM358 and OP365, the amplifiers have different pinouts and are DIP and SO types.
Use the correct +Vsupply voltage to suit the amp you choose.

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Eric
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Markley02

Sorry, typo. You do mean OPA365 right? Not OP365? After looking at the OPA365 Datasheet (http://www.ti.com/lit/gpn/opa365), page 8 Figure 1b, I would just change the Vcm to +2.5V using the ZREF25. My question is why did you list those two resistors over the OPA365 datasheets 10K for the line going from Vin to Vout?

audioguru

The 10k resistor is for negative feedback. The voltage gain of the inverting opamp circuit is the ratio of this feedback resistor to the input resistor. So the gain is -10 in this example if the source resistance is zero.

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ericgibbs

hi Markley,
For your application you require a Gain of *-1 for the -Vin input pin and a Gain of *2 for the +Vin input pins of the amplifier.

Relative to their respective inputs.
The -Gain = Rfeedback/Rinput
The +Gain = 1 + Rfeedback/Rinput [this is why the +Vref =+2.5V, with a gain of *2 it gives an output of +5V]

Do you follow this?

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Eric
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Markley02

I think so, but I am not positive. Let me do some research and look around before I say yes.

shirazmacuff

Hi guys
I’m just putting this out there if precision is not required.
If precision is required then i believe the opamp would be best.
Remember that the gain of the transistor which you would use would have to be considered. You will also need to consider the load on the output.
This circuit was just simulated, so I suggest that you wait for replies before building it.

Attached Images

sine inverter.JPG (37.1 KB, 15 views)

shirazmacuff

what i understood is that he needs to invert the input . 0 in> 5 out, 1 in > 4 out, 2 in> 3 out, 3 in> 2 out, 4in> 1 out and 5 in> 0 out.
at zero input this circiut puts out five volt. i'm sorry , i should have noted that the output is at the collector of the transistor. the problem is that at 5 volt input , the output only drops to approx 0.8 v. this can be circomvented by decreasing the base resistor and choosing a high gain transistor. but this will also have an effect on the signal that is driving this circiut. remember that the input impedence of this circiut is bassically the base resistor.

rjvh

sorry to interupt but i have the same problem but in a different voltage range
my sensor is giving 0 to 10 volt and i need it also on the other way around
my question is do i have to adjust the ref voltage to adjust the voltage range?

ericgibbs

hi,
You could use the same OPA circuits that have been posted, use a potential divider input to reduce the +10V to +5V.

Is this what you mean by:
>>> my sensor is giving 0 to 10 volt and i need it also on the other way around

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"Good enough is Perfect"

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rjvh

it's a pressure sensor that gives a 0V signal with 0 PSI and 10V with 150 PSI
the thing is that my inverter is not switchable to a negative sensor curve so i need a schematic that reverse my sensor out put to 10V at 0 PSI and 0V at 150 PSI in order to get my pump run faster by a falling pressure

ericgibbs

hi,
The LM358 circuit posted earlier uses a dual OPA, keep the circuit for the signal inversion part as already posted.
Use the other half of the LM358 as a non inverting OPA and use a resistive potential divider on the to give a +5V input to the Vin+ of the OPA.

Do you follow that OK?

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Eric
"Good enough is Perfect"

PIC tutorials:
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ericgibbs

hi,
Here is a modified drawing, this will convert 0V thru +10V input, to +5V to 0V output.

Attached Files

LM358A.pdf (11.0 KB, 18 views)

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Eric
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PIC tutorials:
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rjvh

I do understand how to make it but don't see the theory in your story please explane a little bit more
thanks Robert-Jan

rjvh

don't see the drawing?
Robert-Jan