# Measuring an output voltage within a simple circuit does not match the calculation

#### arhzz1

Joined Oct 21, 2020
57
Hello! So I'm facing kind of a problem right here. Im susposed to build this circuit

Now the resistors im using are 1k and 2.2k Ohm, and the input voltage we need to set to 3V,over a GUI that we are executing over python.Now I've connected everything to my PC and whenI measure the outpot voltage I get around 2,9V.This doesnt seem right to me. I've done the calculation per hand like this (3V * 2.2)/ (R1+R2). And I get around 2,06V. Now I'm 99% sure I've done everything right,and still my measerument is way off.Here is how it looks

Can anyone tell me what I'm doing wrong? Thank you in advance!

#### Dodgydave

Joined Jun 22, 2012
11,322

You should be getting around 1V, put the Resistors into the supply feeds directly and twist the ends together with the ADC feed wire to make sure of a better connection.

Do yo have a DVM ?

#### bertus

Joined Apr 5, 2008
22,292
Hello,

Are you trying to measure the DAC output via a voltage divider with the ADC?
In your drawing the 2K2 is at the top and the 1K at the bottom.

Bertus

#### arhzz1

Joined Oct 21, 2020
57
Hello,

Are you trying to measure the DAC output via a voltage divider with the ADC?
In your drawing the 2K2 is at the top and the 1K at the bottom.
View attachment 224206
Bertus
Yes exactly, we are trying to measure the DAC output via a voltage divider. I've tried swapping the resistors already, and I still get the same result

#### ronsimpson

Joined Oct 7, 2019
3,159
Using the picture from bertus, you should have about 2V across the top resistor and about 1V across the bottom resistor. Maybe you wanted to switch the two resistors.

#### bertus

Joined Apr 5, 2008
22,292
Hello,

When you get the same result with swapping the resistors, there must be a bad contact.
Also check the program to measure the voltage.
Try to make the circuit on a different part of the breadboard.

Bertus

#### arhzz1

Joined Oct 21, 2020
57
Hello,

When you get the same result with swapping the resistors, there must be a bad contact.
Also check the program to measure the voltage.
Try to make the circuit on a different part of the breadboard.

Bertus
Okay will do, but what exactly is a bad contact?

#### arhzz1

Joined Oct 21, 2020
57
Yea I've tried it on a diffrent part of the breadboard,still the same.

#### bertus

Joined Apr 5, 2008
22,292
Hello,

As @Dodgydave asked, do you have a Digital Volt Meter?
If so, check the voltage accross the resistors.

Bertus

#### arhzz1

Joined Oct 21, 2020
57
Hello,

As @Dodgydave asked, do you have a Digital Volt Meter?
If so, check the voltage accross the resistors.

Bertus
Unfortunately I dont

#### ronsimpson

Joined Oct 7, 2019
3,159
I'd doubt they would give me 64 Euros for a multimeter
There are much lower cost meters that do less. I remember having 0 money. That also happens when you are much older.