# Function generator with OP AMPS. Prototype in breadboard problems.

#### stryker1803

Joined Dec 15, 2022
6
Hello guys,

I've been working on a function generator project that I want to do but I have encountered some problems. The first one was creating a split power supply rail to power the negative voltage that the TL072CP needs. I manage to create one by watching a video and using a 741 but the function generator still isn’t working on the breadboard. I’m gonna leave some pictures so you guys can help me to discover why and give me some advice. This isn’t the full circuit this is just a fraction built to check the power rail and the first op-amp from the function generator. My last goal from this is to create the full circuit on PCB and solder the components. Keep in mind I’m still a student and fairly new to prototyping.

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#### BobTPH

Joined Jun 5, 2013
6,317
What voltage is your split supply?

What exact part number us your TL072?

#### stryker1803

Joined Dec 15, 2022
6
The TL072 says 21MDBW. As for the split supply I was trying to go for 18v = -+9, but the simulation with the 741 as splits only runs with 7v in the power supply so I’m trying to make it work with that amount of voltage in the breadboard.

#### AnalogKid

Joined Aug 1, 2013
10,227
Per its datasheet, the min operating voltage for a 741 is 10 V.

ak

#### BobTPH

Joined Jun 5, 2013
6,317
The TL072 says 21MDBW. As for the split supply I was trying to go for 18v = -+9, but the simulation with the 741 as splits only runs with 7v in the power supply so I’m trying to make it work with that amount of voltage in the breadboard.
That is not the part number. It should say TL072 with 1 or 2 more letters following.

Most TL072 require at least ±5V.

You 741 circuit will work fine anywhere from 10V to 36V.

Or you can make a ±9V supply using two 9V batteries.

#### MrChips

Joined Oct 2, 2009
28,155
When breadboarding a circuit, use coloured wires intelligently and with purpose. Don’t mix colours on the same lines.

Generally, use red, orange, yellow for +ve supply rails, blue, purple, for -ve supply rails. Use green, brown, black for GND.

#### MrChips

Joined Oct 2, 2009
28,155
You don’t need to use 741 opamp to make a split power supply.
Use two 9V batteries as already suggested.

#### WBahn

Joined Mar 31, 2012
28,192
Hello guys,

I've been working on a function generator project that I want to do but I have encountered some problems. The first one was creating a split power supply rail to power the negative voltage that the TL072CP needs. I manage to create one by watching a video and using a 741 but the function generator still isn’t working on the breadboard. I’m gonna leave some pictures so you guys can help me to discover why and give me some advice. This isn’t the full circuit this is just a fraction built to check the power rail and the first op-amp from the function generator. My last goal from this is to create the full circuit on PCB and solder the components. Keep in mind I’m still a student and fairly new to prototyping.
You want to get in the habit of looking at the datasheets for the parts you use. If you don't do that before you use the part, then you definitely want to look at it as soon as a problem creeps up.

There will be a lot of stuff in the data sheet that you won't understand, especially at first. What you want to look for are things that seem to apply to your situation.

So let's start with the 741 (which is made by a lot of different companies and the specs are not always the same -- so try to find a datasheet from the manufacturer of your specific part, if possible).

Here's a data sheet for the uA741 from Texas Instruments:

From this, you can see that the minimum supply voltage, (Vcc+ - Vcc-), is 10 V. If you operate it with less than this, it may not behave properly.

If you want to create a split supply from a 7 V power source, you need to find an opamp that can operate from this low of a supply voltage (and plenty of them exist).

You also want to look at the requirements for the TL072 that you are trying to use.

Notice that while a specific part, the TL07xH, can operate with only 4.5 V between rails, all of the other parts require a minimum of 10 V.

Another thing you need to be VERY careful about is the input common mode range, which is basically the range of voltages at the inputs of the opamp for it to be happy.

For the TL07xH, the minimum input voltage has to be at least 2 V above the negative rail. That goes up to 4 V for the non-H parts.

#### stryker1803

Joined Dec 15, 2022
6
That is not the part number. It should say TL072 with 1 or 2 more letters following.

Most TL072 require at least ±5V.

You 741 circuit will work fine anywhere from 10V to 36V.

Or you can make a ±9V supply using two 9V batteries.

#### stryker1803

Joined Dec 15, 2022
6
You don’t need to use 741 opamp to make a split power supply.
Use two 9V batteries as already suggested.
You want to get in the habit of looking at the datasheets for the parts you use. If you don't do that before you use the part, then you definitely want to look at it as soon as a problem creeps up.

There will be a lot of stuff in the data sheet that you won't understand, especially at first. What you want to look for are things that seem to apply to your situation.

So let's start with the 741 (which is made by a lot of different companies and the specs are not always the same -- so try to find a datasheet from the manufacturer of your specific part, if possible).

Here's a data sheet for the uA741 from Texas Instruments:

View attachment 283162

From this, you can see that the minimum supply voltage, (Vcc+ - Vcc-), is 10 V. If you operate it with less than this, it may not behave properly.

If you want to create a split supply from a 7 V power source, you need to find an opamp that can operate from this low of a supply voltage (and plenty of them exist).

You also want to look at the requirements for the TL072 that you are trying to use.

View attachment 283163

Notice that while a specific part, the TL07xH, can operate with only 4.5 V between rails, all of the other parts require a minimum of 10 V.

Another thing you need to be VERY careful about is the input common mode range, which is basically the range of voltages at the inputs of the opamp for it to be happy.

For the TL07xH, the minimum input voltage has to be at least 2 V above the negative rail. That goes up to 4 V for the non-H parts.
Thanks for the advice and for taking from your time to write all of this sir,

From now on I’m going to look for the data sheets and check for all of the parameters. I’m going to take your advice and see if I can make the circuit work. If it doesn’t I’m going to do what you guys said and hook it up to some 9v batteries.

G

#### stryker1803

Joined Dec 15, 2022
6
You don’t need to use 741 opamp to make a split power supply.
Use two 9V batteries as already suggested.
If the opamps don't work I think I'm going to go with that option. I just want to create a cool project with opamps and learn more about Electronics and how to do PCB.

#### BobTPH

Joined Jun 5, 2013
6,317
Okay, then it needs ±5V as well.

Edited to add: If you use ±9V, your op amps will work properly with inputs and outputs in the range of ±5V.

#### Audioguru again

Joined Oct 21, 2019
5,595
An opmp is designed to work in linear circuits. They make and amplify excellent sinewaves and triangle waves.
Digital ICs make excellent squarewaves.

When an ordinary opamp tries to make or amplify a squarewave its slopes will be slow instead of switching quickly.

Did you know that the 741 opamp design is 54 years old but some books say it is 59 years old. It was designed to use a +15V and -15V supply. It was too noisy and slow to be used for audio.

I have used many TL07x opamps for stereo audio, some powered by one 9V battery, and used many Cmos digital ICs for digital circuits.