# Amplifiers operational

Hi,

I really need your help! I never used a breadboard and neither a amplifier operational of my life.
However I need one to compare a voltage.
I want to have an output voltage of 5V when the input voltage is higher than 4V and I want 0V when the voltage is lower than 4.
However, my output is always 0,003 and I can’t find why!

Here the datasheet.

I’m posting a photo of my montage and a skretch of the reading of each pin of the amplifier.

I’m more concerned about the way I used the amplifier because all the voltages I put in the amplifier are good to my understanding, so the mountage of the breadboard should be good. The only issue I see is that maybe I missunderstood how to use the amplifier or there is an issue with this one.

Thank you very much,
Max.

What voltage do you measure at pin2 Threshold ?

Try connecting pin 3 to +V and then ground and see what the output does.

Boardburner2: What voltage do you measure at pin2 Threshold ?

4,4V

which is more than 4 !

Check your resistor divider.

Resistor to left of ic looks like its bottom leg is in the wrong strip, ie unconnected.

Boardburner2:
which is more than 4 !

Check your resistor divider.

Resistor to left of ic looks like its bottom leg is in the wrong strip, ie unconnected.

My bad! Threshold is 4!
Input is 4,4

Try connecting pin 3 to +V and then ground and see what the output does.

Same, 0,003

sounds like your ic is fried.

Where did you get the circuit from ?

Take a look at the comparator circuit in the data sheet.

You should really have a decoupling capacitor across the supply and ground close to the ic as well.

Try disconnecting pin3 and measuring the voltage there

You should really have a decoupling capacitor across the supply and ground close to the ic as well.

I don't know what you are talking about :/

I get my circuit from Addisson electronic.

I still get 0,003.

You get.003 on pin 3 the input ? with the input disconnected.

A decoupling capacitor is a capacitor between the gnd and + v rail, amout 01 to 1 uF.

I do not mean where did you buy the chip, i meant where did you get the circuit diagram. These ic's are static sensitive and easily damaged by handling them.

The grey wire at the bottom is obscuring the chip, if there is a notch there you have it upside down.

There is a circle at the top though which is sometimes used.

Boardburner2: You get.003 on pin 3 the input ? with the input disconnected.

A decoupling capacitor is a capacitor between the gnd and + v rail, amout 01 to 1 uF.

I do not mean where did you buy the chip, i meant where did you get the circuit diagram. These ic's are static sensitive and easily damaged by handling them.

I got the diagram thank's to internet with the model of the amp (LM358).

Yeah this is what I get.

The hole in a form of a circle is at the top.

I double checked, the small notch for the 1st pin is at the right place. So I didn't made any mistake for the placement of the pins.

What about the capacitor? I should put one for the supply? Why? Also, I have found one site that put a capacitor for the threshold voltage. Should I put one also?

Thank you

I really need your help! I never used a breadboard and neither a amplifier operational of my life.

Sure , if you promise to stop calling it “amplifiers operational” and start calling it “Operational Amplifiers” (or “OP AMPS” for short)

I’m posting a photo of my montage and a skretch of the reading of each pin of the amplifier.

=> “I’m posting a photo of my breadboard circuit and a schematic of the circuit.”

OP AMP COMPARATORs 101

I want to have an output voltage of 5V when the input voltage is higher than 4V and I want 0V when the voltage is lower than 4.
However, my output is always 0,003 and I can’t find why!

raschemmel: Sure , if you promise to stop calling it "amplifiers operational" and start calling it "Operational Amplifiers" (or "OP AMPS" for short)

Okay It's because in my native language, it's amplifier first and operational second :/

Thank you for the schematic, it's simpler now! I tried to do it like they did in the datasheet but it's not that clear.

I exactly did what's shown in the website you gave me! At least I think. I divided the tension thank's to the resistances. I also provided the input, the supply and ground.

Based on the voltages you posted, (and the behavior of a comparator) , your Vout should be 5V, not 0V.

Pin-3 > Pin-2 (Vin >Vref) => Vout = Vcc (5V)

Since your results are different, can you try the same circuit using the other op amp (pins 5, 6, & 7) ?

It's because in my native language, it's amplifier first and operational second

You're on the forum now , so it's "Operational" first, "Amplifers" second. (English format)

I tried on both op amps of the chip. It doesn’t work.
I even used the second (and same chip) I have, same issue.

HOWEVER, I don't understand why, it works if I put a voltage bigger, 8V. Otherwise it doesn't work even tought the chip is rated 3V-34V if I understood well. New issue, I get a output of 6,73V even thought the supply is 8V. I can live with that but it's wierd. Do you have an idea why?

Adjust supply to match what you are using.
Variable resistor can also be the juntion of 2 resistors.

Yes . It's called "headroom". It's tge amount of voltage necesssry to operate the chip. You need to explain how you are measuring the voltages. What do you mean it works ?

CrossRoads:
Adjust supply to match what you are using.
Variable resistor can also be the juntion of 2 resistors.

Thank you! I just need to add the capacitors!

I mean it works because I translated my analogue signal to a digital! When below 4V it's 0 and when higher it's the output of 6,something.

However I got some news! For a reason I TOTALY don't understand, when I using the 5V pin of the arduino, it doesn't work, but when I use a 5V battery. It works! Why?
The headroom is about 1.3V thought. Seems big.