# OP AMPS, mV, sensor

#### GTronics

Joined Jan 30, 2021
7
Hello everyone,
Lets imagine a situation where 1 Bar of pressure represents 1 milivolt (0.001V), and I want to read with arduino, as I've been searching and foundo some info about adc where arduino has 10bit adc capacity so minimium voltage is 5V/1023bits=0.005mV; so I tried to make a circuit in proteus 8 where I input 5millivolts at A0 port and made it to show in a LCD 16x2, however it does not read because only show 3 digits on display (0.00), so anyone knows if I can get a 4 digit reading with some code, or I will need a OP-Amp?

#### wayneh

Joined Sep 9, 2010
17,152
I believe you’ll want an op-amp to condition the sensor signal, to amplify it 20X or so. That will give you a voltage you can read more precisely with your ADC. Look up “instrument amplifier”, or IA op-amp circuits.

Do you know what your maximum pressure and voltage will be? You can set your IA gain to give the power rail voltage (max output) at that maximum input.

#### GTronics

Joined Jan 30, 2021
7
I believe you’ll want an op-amp to condition the sensor signal, to amplify it 20X or so. That will give you a voltage you can read more precisely with your ADC. Look up “instrument amplifier”, or IA op-amp circuits.

Do you know what your maximum pressure and voltage will be? You can set your IA gain to give the power rail voltage (max output) at that maximum input.
I am just theorizing that idea, I believe a lot of people would be grateful actually, so the pressure was only a way to understand what I want to say,Talking only about voltages lets say the max voltage is 2V, with a 20x amplifier I wouldn't be able to use arduino

#### ericgibbs

Joined Jan 29, 2010
12,901
hi GT,
What is the maximum Bar pressure the project will be required to measure.?

E

#### GTronics

Joined Jan 30, 2021
7
hi GT,
What is the maximum Bar pressure the project will be required to measure.?

E
Imagine something to 1V not real pressure obviously cuz it would mean about 100bar

#### ericgibbs

Joined Jan 29, 2010
12,901
that means arduino will +1 each 4.88mlV right?
Yes

What is the maximum Bar pressure the project will be required to measure.?

#### GTronics

Joined Jan 30, 2021
7
that means arduino will +1 each 4.88mlV right?
Yes

What is the maximum Bar pressure the project will be required to measure.?
10Bar
Uhhh then if i use 1.1V internal reference i get 1mV, my problem then is how do I I see 1 unit and 3 decimal in a lcd because It only see 1 shows me 1 unit and 2 decima

#### ericgibbs

Joined Jan 29, 2010
12,901
hi,
So 10 Bar at say 1mV/Bar, that's 10mV.
Using Vref of 5V , you use a OPA to amplify the 10mV to say 0.5Volt.
For a 1023 max count for a 5V analog input, for 0.5V you would get (0.5/5v)*1023 = 102 counts
The LCD should be set to show 10.2 Bar

E

#### ericgibbs

Joined Jan 29, 2010
12,901
hi.
If you used a 1.1Vref and assumed a max Bar voltage of 9.99mV, multiply that by 111 == ~1.1V

So the ADC count would be 1023, which show on the LCD as 10.23Bar

As you only have a 9.99 Bar maximum LCD display., you would use a Gain pot on the OPA to reduce give to give 9.99Bar max.