# HELP with function generator using OpAmps!

#### Narrin

Joined Oct 2, 2011
47
Okay capacitors block dc while allowing ac, so i need to place a capacitor at one of the inputs but where?

#### Audioguru

Joined Dec 20, 2007
11,248
Okay capacitors block dc while allowing ac, so i need to place a capacitor at one of the inputs but where?
I deleted the power supply wires from your schematic and replaced them with symbols.
I cropped your schematic so it is not as big as my neighbourhood.

U1B was DC-coupled and has a voltage gain of ten times and amplified the DC offset voltage of the square-wave. I added a coupling capacitor to block the DC.

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#### Narrin

Joined Oct 2, 2011
47
Adding a 0.1uF capacitor did block the dc offset and now there is only a 100mV difference in the peak to peak of the triangular and sine wave. Thanks! Now all i have to look at is changing the gain so that all the waves are at the same amplitude.

#### Narrin

Joined Oct 2, 2011
47
Okay so the capacitor after the output of U1A causes the slopes of the triangular wave to be not that linear and it also alters the sine wave a bit.

Other than that, to bring all the waves to the same amplitude i used voltage dividers to reduce the voltage for the outputs of U1A and U1C which are the square and sine waves. For the triangular wave i passed the output through an opamp U2.

I was trying to put in a switch for the amplitude, i used a TL031 opamp like U2 after the output of the switch S1 and i was varying one of the resistors according to the formula for the Gain of a non inverting amplifier
Gain = 1+ (Rf/Ri)
but in the output the shape of the sine and triangular waves changed and the output was not as high as i wanted...how can i implement a switch to change the amplitude of these waves..and well the frequency

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#### SgtWookie

Joined Jul 17, 2007
22,230
As in the 555-based signal generator, you need to use U2 with a feedback resistor, and route the outputs of the various stages through S1 with appropriate resistors.