Circuit not functioning as expected

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0x00x0

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I am trying to make this work. I expect to get a 54 volt peak voltage from the points on the upper right side of the circuit. Instead I get 4 volts.

The circuit is calling for 2 LM358's, I have LM358N's

I THINK they are the same thing.. I have tried different LM358N's, they all do exactly the same thing.. I have gone over my work several times, and cannot find any deviations from the schematic. Any ideas gladly accepted..

**broken link removed**
 
Hi 0x00x0,

Measure again between pin 1 of the LM358 and gnd,
and also between pin 7 and gnd.
In both cases you should measure about 24 volt pp.

on1aag.
 
As long as you're at it, measure all the pins on the 358 as they enter the IC package, preferably with a scope.
There can't be too much that can go wrong with this circuit.
 
Ok, here are my results with my Digital multimeter, no scope available to me..

U1B
pin 1 to ground: fluctuation from 11.3 to 14.9 vdc
pin 2 to ground: 7.4 vdc
pin 3 to ground: fluctuation from 12.1 to 13.1 vdc
pin 4 to ground: 0 vdc
pin 5 to ground: 0 vdc
pin 6 to ground: 0 vdc
pin 7 to ground: 25.5 vdc
pin 8 to ground: 26.9 vdc

U1A
pin 1 to ground: 0 vdc
pin 2 to ground: 0 vdc
pin 3 to ground: 0 vdc
pin 4 to ground: 0 vdc
pin 5 to ground: fluctuation from 12.3 to 13.1 vdc
pin 6 to ground: fluctuation from 11.5 to 14.8 vdc
pin 7 to ground: 0 vdc
pin 8 to ground: 0 vdc
 
Last edited:
Hi 0x00x0,

Rebuild the circuit with only one LM358.
You are only using one half of each integrated circuit.
The circuit should generate a square wave with a frequency
of about 4 hurts. You should be able to see a led blink at
a rate of 4 times a second when connected from pin 7 to
gnd, with a 4k7 resistor in series with the led.

on1aag.
 
The second LM358 (U1A) does not have its power supply pins 8 and 4 connected to the power supply so of course that opamp doesn't work.

The LM358 has two opamps inside so only a single LM358 is needed for this circuit.
Next time you make a circuit, look at the datasheet for its IC.
 

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palanisamy said:
why u didn't use the pins 5,6 & 7th pins of U1B
Click to expand...
Dunno, I have a family member who wanted me to build this for them, they gave me the schematic and I just followed it..


audioguru said:
The LM358 has two opamps inside so only a single LM358 is needed for this circuit.
Next time you make a circuit, look at the datasheet for its IC.
Click to expand...
I didn't design it.. The instructions say:


I think that the reason he designed it with 2 opamps is to get the 180 degree out of phase situation.. I don't know for sure.. I am relatively new to electronic circuit design, in case you couldn't tell

palanisami said:
connect the 8th pin of U1A to 27 vdc and try once again
Click to expand...
on1aag said:
And connect pin 4 to gnd !

on1aag.
Click to expand...

I will give this a try and report back.. Thanks everyone for all the input!!
 
Last edited:
It says, "the first section and the second section of the dual opamp. One LM358 has both opamps inside.
 
Well that seems to have worked.. I am getting a much higher voltage fluctuation, my meter does not give me exact figures since it is switching polarity so quickly. .

Once again, thanks for the assist, you guys are great!

audioguru said:
It says, "the first section and the second section of the dual opamp. One LM358 has both opamps inside.
Click to expand...

So this circuit will do with one chip what they describe? I wonder what the purpose of having 2 is then.. Perhaps the designer of the circuit didn't realize it..
 
The project uses only a single LM358 dual opamp that is labelled U1. That is why its second section does not have power supply pins and that is why each opamp has different pins numbers.
 
Last edited:
Ah, now what you say becomes clear.. I shall have to rewire this then..

Thanks for clarifying that!
 
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