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Construct a Schmitt Trigger using the 741 Op Amp

Draw the Schmitt Trigger circuit you constructed. Identify the values of all components

To construct the circuit above I am going to use the following components and voltages:

1. [math]R_1 = (1\pm)\ k\Omega[/math]
2. [math]R_2 = (1\pm)\ k\Omega[/math]
3. [math]R_3 = (10\pm)\ k\Omega[/math]
4. [math]\mbox{OP}\ \mbox{AMP}\ 741[/math]
5. [math]V_{ref} = V_{cc} = (15\pm)\ V[/math]

Identify the input voltage threshold levels at which a [math] V_{in}[/math] will produce [math]V_{out} \approx V_{cc}[/math]

Because

[math]R = R_1 = R_2 = 1\ k\Omega \ll R_3 = 10\ k\Omega[/math]

we can use the approximate formula to calculate the threshold voltages (ch.10.19 the Schmitt Trigger "Introductory electronics for scientists and engineers"):

1) if the output is high:

[math]V_2 \cong \frac{V_{ref}}{2} + \frac{R}{2R_3}V_{cc}[/math]

2) if the output is low:

[math]V_2^' \cong \frac{V_{ref}}{2} - \frac{R}{2R_3}V_{cc}[/math]

By substituting the actual values and doing math and error propagation we find:

[math]V_2 \cong \frac{(15\pm 0.01)\ V}{2} + \frac{(1\pm 0.01) k\Omega}{2\cdot(10\pm 0.01) k\Omega}(15\pm 0.01)\ V = (8.25\pm 0.009)\ V[/math]

[math]V_2^' \cong \frac{(15\pm 0.01)\ V}{2} - \frac{(1\pm 0.01) k\Omega}{2\cdot(10\pm 0.01) k\Omega}(15\pm 0.01)\ V = (6.75\pm 0.009)\ V [/math]

Compare the threshold values to what is expected.

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