Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Level Shifter-Temp Sensor

Status
Not open for further replies.

tbr75

New Member
Hello again,

I am currently using an LM335 temperature sensor to detect temperatures in the range of -40 deg Celsius to 30 deg Celsius. It is currently tuned with a pot to where it outputs 2.8volts at 30 deg Celsius. This is the lowest I can get it to output with the pot; the problem with that is the Vref on my Atmel 8951 is 2.8volts. So what I would like to do is shift the voltage down 2.1volts (The 2.1volts comes from the sensor being rated at 10mv/deg C; so if I'm going down to -40deg Celsius from +30 that's a difference of 700mv so the lowest voltage it will currently output is 2.1volts)

By shifting the voltage down 2.1volts, I can then send the output through an amplifier to create an output of 2.8volts again at 30 deg Celsius but now I will be using 0 to 2.8volts instead of 2.1 to 2.8 volts which gives much better resolution. How can this be achieved? Are there other ways to improve the resolution?

Thanks, Trent
 
I've attempted to use a two stage amplifier, the first stage being a difference amp and the second stage amplifying back to 2.8volts. Not sure what I was doing wrong but it wasn't working.

If I just amplify it down, when I go to amplify it back to 2.8volts will I not be at the same 2.1 to 2.8volts range?

Trent
 

Attachments

  • OpAmpCircuit.png
    OpAmpCircuit.png
    15.9 KB · Views: 163
Last edited:
Trent,

Here you go. You will need a 5.00V+-0.02V reference, and some 1% resistors. The three green plots are at V(ref) = 4.98, 5.00 and 5.02V to show the dependence on V(ref).
 

Attachments

  • TempSensor.png
    TempSensor.png
    44.4 KB · Views: 163
Last edited:
If you use an LM334 instead(temperature dependent current source) with two resistors you can set the scale factor and voltage into the ADC.
 
Trent,

Here you go. You will need a 5.00V+-0.02V reference, and some 1% resistors. The three green plots are at V(ref) = 4.98, 5.00 and 5.02V to show the dependence on V(ref).

Mike,

Thank you for your help. I tried something similar but I guess I missed something. I redesigned the circuit for my specs (looks like you accidentally did -30 to plus 40 instead of -40 to plus 30) and it works great.

I have a question though, at my disposal are only LM324 op amps which are not rail to rail. However, my LM324 for LTspice shows a nice line from 0 to 2.8 on the output. Will it still work or will it come back with incorrect readings as it gets closer to 0volts output?
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top