Difference between revisions of "GradFinalLab RS"

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==Identify the input voltage threshold levels at which a <math> V_{in}</math> will produce <math>V_{out} \approx V_{cc}</math>==
 
==Identify the input voltage threshold levels at which a <math> V_{in}</math> will produce <math>V_{out} \approx V_{cc}</math>==
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The theory does say (ch. 10.19 The Schmitt Trigger R. Simpson "Introductory electronics for scientists and engineers"):
 
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<math>V_2 = \frac{R_{123}}{R_2}V_{ref} + \frac{R_{123}}{R_3}V_{out}</math>
 
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1) if the output is high:
 
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<math>V_2 = \frac{R_{123}}{R_2}V_{ref} + \frac{R_{123}}{R_3}V_{out_1}</math>
 
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2) if the output is low:
 
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<math>V_2^' = \frac{R_{123}}{R_2}V_{ref} - \frac{R_{123}}{R_3}V_{out_1}</math>
 
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where
 
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<math>R_{123} = (R_1 || R_2 || R_3) = \frac{R_1 R_2 R_3}{R_1+R_2+R_3}</math>
 
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and <math>V_{out_1}</math> and <math>V_{out_2}</math> approximately equal to supply voltage <math>V_{cc}</math>
 
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The actual measured values of high and low output voltages (they do not really equal to <math>\pm V_{cc}</math>) are:
 
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# <math>V_{out_1} =  (+11.06\pm0.01)\ V</math>
 
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# <math>V_{out_2} =  (-10.54\pm0.01)\ V</math>
 
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Substituting all quantities in the formulas above:
 
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<math>R_{123} = (1.01\pm 0.01)\ k\Omega || (1.01\pm 0.01)\ k\Omega || (5.10\pm 0.05)\ k\Omega = (0.459\pm 0.003)\ k\Omega</math>
 
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<math>V_2 = \frac{(0.459\pm 0.003)\ k\Omega}{(1.01\pm 0.01)\ k\Omega}(11.90\pm 0.01)\ V + \frac{(0.459\pm 0.003)\ k\Omega}{(5.10\pm 0.05)\ k\Omega}(11.06\pm 0.01)\ V</math>
 
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<math>V_2^' = \frac{(0.459\pm 0.003)\ k\Omega}{(1.01\pm 0.01)\ k\Omega}(11.90\pm 0.01)\ V - \frac{(0.459\pm 0.003)\ k\Omega}{(5.10\pm 0.05)\ k\Omega}(10.54\pm0.01)\ V</math>
 
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and doing math and propagating errors we end up with the following predicted threshold voltages:
 
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1) If the output voltage is high the threshold voltage are:
 
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<math>V_2 = (6.41\pm 0.07)\ V </math>
 
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1) If the output voltage is low the threshold voltage are:
 
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<math>V_2 = (4.46\pm 0.06)\ V </math>
 
  
 
==Compare the threshold values to what is expected.==
 
==Compare the threshold values to what is expected.==

Revision as of 03:18, 27 April 2011

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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

Schmitt trigger 01.png

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

  1. [math]R_1 = (1.01\pm0.01)\ k\Omega[/math]
  2. [math]R_2 = (1.01\pm0.01)\ k\Omega[/math]
  3. [math]R_3 = (5.10\pm0.01)\ k\Omega[/math]
  4. [math]\mbox{OP}\ \mbox{AMP}\ 741[/math]
  5. [math]V_{ref} = (+11.90\pm0.01)\ V[/math]
  6. [math]V_{cc} = (+11.90\pm0.01)\ V[/math]
  7. [math]V_{ee} = (-12.11\pm0.01)\ V[/math]

Graph [math]V_{out}[/math] as a function of [math]V_{in}[/math]. Is there a hysteresis loop?

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

Compare the threshold values to what is expected.

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