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I'm trying to make a square wave generator with an adjustable range of output signal amplitude (between 0 and 5V) using an LM741 op-amp and the following circuit:

50% duty cycle square wave genertor, credit to https://www.electronics-tutorials.ws/opamp/op-amp-multivibrator.html

The thing is, VOUT is limited by the saturation voltage which in this chase is +-15V but from what I understand it can be varied with a voltage divider formed by R1,R2 in regular inverting amplifier circuits. In my case, R1 and R2 (alongside τ=RC) only help adjust the output frequency with the formula for the period T=2RC*ln(1+β/1-β,), my output amplitude still being stuck between ≈+-VCC.

Edit with exactly what I need: I want that my peak-to-peak amplitude to be adjustable, not stuck between ≈+-VCC. For example, with a potentiometer, voltage divider or anything to make amplitude in the range of 0-5V. I can't find a way to make it adjustable.

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  • \$\begingroup\$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. \$\endgroup\$
    – Community Bot
    Oct 13, 2021 at 16:39
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    \$\begingroup\$ Instead of trying to convert the -14V to +14V output to 0V to 5V on that circuit that uses an antique 53 years old 741 opamp, it is much easier to use a modern rail-to-rail opamp powered from 0V and +5V, then add a "volume control" to its output. Tell your teacher about modern opamps. \$\endgroup\$
    – Audioguru
    Oct 13, 2021 at 16:50
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    \$\begingroup\$ Hey I'm 69 yrs old and I still use my old designs (lol) \$\endgroup\$ Oct 13, 2021 at 17:02
  • \$\begingroup\$ Here's my SIM with a 741 and an ideal comparator / OA tinyurl.com/yzk28r7w \$\endgroup\$ Oct 13, 2021 at 17:14
  • \$\begingroup\$ Thank you for the SIM, but that was my problem, the output amplitude is still +-VCC \$\endgroup\$
    – PowerTb321
    Oct 13, 2021 at 17:23

2 Answers 2

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Your circuit generates a square wave at the output of the opamp. This is part of the oscillator signal path.

You can use that +/- 15 V signal to generate a 0..5 V signal -- e.g. use it to drive a 4.7 V zener diode via a 10k resistor. This will give about +4.7 V and -0.6 V out.

If you want an adjustable output, you could just put another R divider from Vout to GND. This may not give precisely 0 and 5 V levels. If you want that, you will need another gain stage -- even a CMOS inverter (e.g. CD4007) would work. Just drive the +/- 15 V signal into it and power it from +5 V and 0 V.

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You have a non-rail-to-rail Op Amp with hysteresis which means the output will it NOT be 50% duty cycle NOR rail-to-rail.

The negative feedback RC integrator will slew towards the ratio of those two voltage levels.

This means there is no mechanism to offset voltage, gain without affecting frequency and/or duty cycle.

CMOS LOGIC Schmitt Triggers with 1/3 Vdd hysteresis will work much better for you. Then add any gain and offset outside the loop. And use nonlinear feedback to change duty cycle with diodes and a pot to change f.

But in future define specs for what you wish to do, then find a way to do it.

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