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

[Zigie]

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.

 

[berkeman]

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.

 

[berkeman]

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.

 

[Zigie]

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?

 

[Zigie]

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]

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?

 

[berkeman]

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.

 

[Zigie]

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.

 

[Zigie]

Better yet this page on that website has a calculator for that circuit

http://www.daycounter.com/Calculators/Op-Amp/NonInverting-Op-Amp-Resistor-Calculator.phtml

Could anyone let me know what I should be entering as the inputs to this calculator?

Vout 4(V)
Gain ?
R1 ? (KOhms)
V1 (Input lead) 1 (V)
V2 (non-zero only if offset is requred) ? (V)
Vp ?(V)
Vn ?