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Simple Dual Op Triangle Generator Issues

NeonStreak

Nov 26, 2022
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Nov 26, 2022
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Hello, I am fairly new to electronics. I have been trying to make a simple LFO to control an audio circuit's volume.

I am having trouble with the oscillator itself. It looks like it works fine in LTspice, but when I build the same circuit on a breadboard it doesn't seem to work. I was sure I would run into this sort of thing but I don't know what to do to make it function properly irl. I am using the dual op: TL072AC.

my meter shows around 8v dc on the square output and around 1.5v dc on the triangle output, and my scope doesn't read anything that is helpful.

If anyone can point out and explain what is wrong that would be great! Thanks!
 

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kellys_eye

Jun 25, 2010
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but when I build the same circuit on a breadboard
Did you build it correctly? Show us the actual build. Did you connect the points marked 0V to actual ground and did you use a split rail power supply?
 

crutschow

May 7, 2021
550
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You likely have a wiring error.
Double check all the connections
After that, if it's still now working, measure all the node voltages and show them on your schematic posted here.

Why do you have the +P voltage to the op amp shown as 4.5V?
It should be 9V.
 

NeonStreak

Nov 26, 2022
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Nov 26, 2022
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You likely have a wiring error.
Double check all the connections
After that, if it's still now working, measure all the node voltages and show them on your schematic posted here.

Why do you have the +P voltage to the op amp shown as 4.5V?
It should be 9V.
It shows that just so I can keep my head straight. The "0v" is the reference voltage for the op amp.
 

NeonStreak

Nov 26, 2022
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Nov 26, 2022
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Hey guys, thanks for your responses, I had some time to spend figuring it out. Thanks to you I took a closer look at my breadboard. turns out I had the voltage divider at U1 in the wrong order. works a treat now.

This issue is solved.

Thank you guys again, I have to take more care when assembling try to make my schematics easier to look at so I don't misplace components.
 

crutschow

May 7, 2021
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It shows that just so I can keep my head straight. The "0v" is the reference voltage for the op amp.
That's bad form.
It may help keep your head on straight, but it puts a kink in ours.
Normally all voltages should be referenced to ground/common.
 

NeonStreak

Nov 26, 2022
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Nov 26, 2022
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That's bad form.
It may help keep your head on straight, but it puts a kink in ours.
Normally all voltages should be referenced to ground/common.
Good to know. In the future I will make sure to label it as "ref" or the like to make it easier to look at/understand.
 
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