Amplifying a 10-70mV signal to 0-5V range

Hi, i got two devices,

Fuel cell sensor:
https://www.dart-sensors.com/wp/wp-content/uploads/2014/10/BA-R-Sensor-Datasheet.pdf

Pressure sensor:
http://shoky.tw/UniSence/UniSence/ATM%20pressure%20package.pdf?Part=dow-THERMOPILESENSORS&Nbr=2&Category=0

Both these devices give out a voltage about 10mV-70mV at the maximum and i was wondering if anyone help me find an op-amp to amplify this signal to 0-5V range so i can read it by the microcontroller, or atleast point me in the right direction to choose one, please.

Also i was wondering if i can use a single op-amp for comparing(or adding) these two signals and then giving out a single output to the arduino.

Any help is much appreciated, thanks.

The fuel sensor has an "application circuit" with output for a 5volt A/D on page 5.
It is even available from the manufacturer if you can't build it yourself.

Amplifying the pressure sensor was explained in your previous thread.

The Arduino can compare/calculate/whatever with the values of the two sensors.
Leo..

Hi,
The "Fuel Cell Sensor" which is a "Breath Alcohol Sensor" has a suggested circuit to give you an output in its application/data sheet.

The pressure sensor is a Wein Bridge strain type sensor, so you will need something like a HX711 bridge amplifier.

https://create.arduino.cc/projecthub/MOHAN_CHANDALURU/hx711-load-cell-amplifier-interface-with-arduino-fa47f3?ref=search&ref_id=hx711&offset=0

What is the application?

Tom... :slight_smile:

Hi, thanks for the replies. I got a question again:

I've got like 12-13 op amps that my local electronic store sells and the input offset voltage of all these op=amps start with 2mV to around 8mV. Now this is the signal i get from both the fuel cell sensor and the pressure sensor. The one that you guys mentioned( from the datasheet of the fuel cell sensor )has an offset voltage at 2microV but it is a surface mount op-amp and also not available at my place.

i was wondering what difference does this parameter bring to the design. I've looked up many sources on what input offset voltage is and haven't got any clarification onto it. If the input offset voltage is around 2 to 8mV then does that mean my output signal from these sensors is not sufficient enough to give it as input to the op-amp ??

If the input offset voltage is around 2 to 8mV then does that mean my output signal from these sensors is not sufficient enough to give it as input to the op-amp

No an input offset is like a phantom voltage that is added to the real voltage. It matters because if you are amplifying a real signal by a lot then the offset voltage can swamp the real signal. With high gain you could reach the full rail voltage with just the offset voltage.

If however you want to amplify only AC signals then do it in two stages, after the first stage couple into the second stage with a capacitor and that removes the D.C. offset given by the first stage.

Such opamps are usable, but you must compensate for the offset either in hardware ( a nulling pot) or software.

What sort do you have?

Allan

An "instrumentation amplifier" is an opamp with a specific configuration which is useful for this type of work. The gain is set with a single resistor.

Almost any opamp with "INA" in the part number will do for you.

indy37:
I've got like 12-13 op amps that my local electronic store sells and the input offset voltage of all these op-amps start with 2mV to around 8mV. Now this is the signal i get from both the fuel cell sensor and the pressure sensor. The one that you guys mentioned( from the datasheet of the fuel cell sensor )has an offset voltage at 2microV but it is a surface mount op-amp and also not available at my place.

Sadly, the reality is most likely that your "local electronic store" will not sell any important part for a specific application.

And you do not buy a bare HX711 chip anyway. The reality is that you buy a ready-to-use module.

(I'm not here to sell you stuff, this is just how the world works now. :astonished: )

MorganS:
An "instrumentation amplifier" is an opamp with a specific configuration which is useful for this type of work. The gain is set with a single resistor.

Almost any opamp with "INA" in the part number will do for you.

Hi i've looked for op-amps and i got only this one available:
INA126PA
DS:http://www.ti.com/lit/ds/symlink/ina126.pdf

the problem is in the page 13 of the datasheet it, where it mentions trimming of offset voltage it again uses OP237, which wasn't available and so i decided to use this in the first place. Coz in the datasheet of the fuel cell sensor it uses OP335 and that was SMT and wasn't avilable.

So can i use the 126PA without the 237 ?

Also can i use the same one for the pressure sensor amplification as well?

So can i use the 126PA without the 237 ?

Yes.

The offset voltage is only 0.25 mV, if you want to trim it then use any op amp in the circuit of page 13, there is nothing very special about it.