Temp sensor

I had it working, but now it seems like it cant find a solution for some reason

What exactly is your desired outcome? And I've found out that if you set the input voltage as greater than 80mV, then the led shines. However, it doesn't stop shining for any value you give the input even uptil 1KV

The leds are just my effort to add 3.2v at the end

My project is to simulate a temp sensor that will take in C as a mV value and convert it to F. For example 21.1 C = 21.1 mV then convert that to 70 F. But the mV output has to bee 100 times the temp in F so 70F would be 7000mV or 7V

The conversion from C to F is F= 1.8C +32. I have the C times 1.8 part, but i cant figure out a way to add 3.2V without adding another power supply

Like this? http://everycircuit.com/circuit/5275238278627328

Yea i like it. It is a lot simpler than the solution my book proposed. They used three op amps, one to amplify, one to invert and than one to sum the 3.2v. But I guess he did say to only use the 15v power supply that supplies the op amp. I'm going to update it his suggested solution

That is, if i can get it figured out

If you wan't to use the circuit I linked here in chat, you may need to add a voltage follower to the input, and add a voltage follower at the DC offset section (assuming you derive 3.2V from 15V using a voltage divider, and use resistors above 10K).

Thank you sir

You're welcome, bsburns2506.

Here is one variation: http://everycircuit.com/circuit/6443919830417408

Very nice solution

Thanks ...Here is a full F to C and vice versa version: http://everycircuit.com/circuit/5362322511233024 And yet a different variation here:  http://everycircuit.com/circuit/5785433417187328

@bsburns http://everycircuit.com/circuit/5275238278627328

@bsburns this is what I was talking about before. Since we don't know out output resistance of your sensor, this may be an improvement.

@crake yes that is the exact solution he talked about. Its hard for me because its an audio lecture and i cant see his results. I can only hear his description of them and this is spot on

That looks good ... a little more playing on that crake version above here: a 111 Ohm calibration resistor to enable higher C input? http://everycircuit.com/circuit/5765474435727360

@bsburn2506 Glad this helped. If you haven't already, look into op amp characteristics like input and output resistance, and negative feedback etc. Mess with the most basic amp topology first and then increase the complexity once you're sure you have a grasp on characteristics. The amp here has a lot going on. It has signal gain, addition, buffering etc.

@crake The series ive been listening to has done a few lectures on opamps. I think that no current goes through the input and that with feedback, both the pos and neg inputs are almost the same. But they are still pretty new to me. Trying to decipher your circuit is helping me

@crake i was able to remove the summing amp and its feedback resistor without any effect on the output. What is the purpose of that amp?

@bsburns2506 This amp was a buffer providing a low output resistance and a DC offset voltage. The low output resistance seen by the 180kohm resistor helps maintain the balance of the difference amp at the center, as well as maintains the DC offset voltage provided by the voltage divider. Since you chose low resistor values for your voltage divider, this potential problem isn't obvious. Make a spreadsheet with pairs of resistor values for your voltage divider. Start with 3kohm and 817ohm and then increase their values. Take the pairs of resistor values from the spreadsheet and then try them in the simulator. You will see that the output resistance from your voltage divider begins to interact with the 180kohm resistor for ever increasing values of the resistor pairs.

Check out this source. Analog devices rocks and I would encourage anyone to check out their articles, as well as Ti and others but, here you go... scroll down about half way. You will see something very similar to what you're working with here. http://www.analog.com/en/analog-dialogue/articles/common-problems-when-designing-amplifier-circuits.html

Thank you sir. I will dive into that recommendation

Thanks to everyone involved in this. Its been an awesome learning experience

@bsburns2506 I am glad we could help. Keep at it. After sometime you will get to where you want to be, and then some :D