How Can I Convert a -0.1V to 1V Output Into a 0V to 4V Range for an ADC Input?

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Discussion Overview

The discussion revolves around designing a circuit to convert the output range of a thermal sensor, which is -0.1V to +1V, into a 0V to 4V range suitable for an ADC input. The context includes theoretical and practical aspects of electronics, particularly focusing on operational amplifiers (op-amps) and circuit design.

Discussion Character

  • Homework-related
  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant describes the need to design a circuit that connects a thermal sensor output to a microcontroller's ADC, specifying the output range requirements.
  • Some participants suggest using op-amps to achieve the necessary gain and offset adjustments for the signal.
  • There is a proposal to shift the DC output to ensure the minimum output is at 0V and then amplify the maximum output to reach 4V.
  • One participant expresses interest in clamping circuits using diodes but questions their applicability to DC signals.
  • A participant shares a link to an op-amp level shifter circuit, indicating it might meet their needs but seeks guidance on modifications.
  • Another participant notes confusion regarding the components in the shared circuit, particularly the reference voltage and the implications of changing voltage ranges.
  • A participant mentions a calculator for non-inverting op-amp circuits and seeks input on what values to enter for their specific application.

Areas of Agreement / Disagreement

Participants generally agree that op-amps are a suitable approach for the circuit design, but there are differing opinions on specific implementation details and the applicability of certain circuit types. The discussion remains unresolved regarding the exact configuration and component values needed for the desired output.

Contextual Notes

Participants express uncertainty about the specific roles of components in the proposed circuits and the adjustments needed for their particular voltage ranges. There are also limitations in their understanding of op-amps and circuit design principles, which may affect their ability to implement the solutions discussed.

Zigie
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Homework Statement


I am given a thermal sensor that measures temperature at 10mv/degree C. We are to measure a range of -10 to 100 degrees C. Design a circuit that will connect the thermal sensor to a micro controller with an A/D Converter the must take an input from 0 to 4v.

http://www.national.com/mpf/LM/LM35.html#Overview (thermal sensor datasheet)

So I guess my question is how would I design a circuit that would take a output range of -.1v to +1v into 0v to 4v?

Homework Equations



N/A

The Attempt at a Solution



My electronics experience is limited, I am just taking an electronics course but this is for a general engineering class so I am stumbling a bit on how to implement this. I imagine I will have to use transistors and/or diodes to accomplish this.
 
Last edited by a moderator:
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Zigie said:

Homework Statement


I am given a thermal sensor that measures temperature at 10mv/degree C. We are to measure a range of -10 to 100 degrees C. Design a circuit that will connect the thermal sensor to a micro controller with an A/D Converter the must take an input from 0 to 4v.

http://www.national.com/mpf/LM/LM35.html#Overview (thermal sensor datasheet)

So I guess my question is how would I design a circuit that would take a output range of -.1v to +1v into 0v to 4v?

Homework Equations



N/A

The Attempt at a Solution



My electronics experience is limited, I am just taking an electronics course but this is for a general engineering class so I am stumbling a bit on how to implement this. I imagine I will have to use transistors and/or diodes to accomplish this.

Welcome to the PF.

Have you started to study opamps yet? That's typically how you would accomplish this.

You basically need to have some control over the gain and offset of your interface circuit. Try searching a bit with key words like: opamp circuit gain offset tutorial.
 
Last edited by a moderator:
berkeman said:
Welcome to the PF.

Have you started to study opamps yet? That's typically how you would accomplish this.

You basically need to have some control over the gain and offset of your interface circuit. Try searching a bit with key words like: opamp circuit gain offset tutorial.

Actually, those search terms don't work all that well (I just tried them). Opamps have their own gain and offset issues, so that is what most of the hits are for.

Instead, look at opamp circuits that let you change a signal's offset, and then look at typical non-inverting opamp gain circuits.
 
Thanks for the reply guys!

Instead, look at opamp circuits that let you change a signal's offset, and then look at typical non-inverting opamp gain circuits.

So basically I would take the DC output and shift it up a certain offset and then use another op amp to amplify it up?

If this is true should I just be offsetting so the minimum possible output is shifted to 0v and then boost the maximum possible output after the shift to 4v?
 
While searching around the internet for these I stumbled across Clamping using diodes. I think this would work great for what I need but I think these circuits can only be applied to AC signals because of the capacitor. Is there something like this type of circuit for DC signals?
 
Zigie said:
I found this circuit
http://www.daycounter.com/Circuits/OpAmp-Level-Shifter/OpAmp-Level-Shifter.phtml

I think this does exactly what I am looking for, but I guess I'm unsure of how to change it to my needs. Does anyone have any ideas of how I could use this to do accomplish my goal?

Yes, good. That is the type of circuit that you can use. Have you learned about opamps yet? Will you be learning them in the class you are in now? If so, read the intro sections of the book about opamps, and that should give you the tools to modify the resistor and voltage values in the example circuit that you found.
 
I have learned about op amps but only breifly, we haven't went into depth about them yet in my course.

I think what's happening in this circuit is they are using a voltage divider first, and then using a non inverting amplifier to boost the voltage. I am not really sure what the R? and C? are doing.

Perhaps you could help me by explaining what exactly is happening in this circuit so I could better understand how I could tailor it to meet my needs
.
I guess I am a little confused on what the 1.6v ref is on the circuit diagram and why they choose 3.3v as for the opamp. Also since they are decreasing their voltage range from -5 to +5 to 0 to 3.3 volts does this change how I would use this circuit. In my example I need to increase from -.1 to 1v into 0 to 4v.
 

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