UChicago Instructional Physics Laboratories

Parts:

Parasitic Oscillations: a sine wave with a “gentle slope” would be something like 1 HZ* at 30 mV amplitude.  For a gentler (i.e. less steep) slope, either lower the frequency or lower the amplitude.

• You'll want to use the -20 dB button here to get the amplitude small enough.
• You can definitely get a lot of spikes, but you may not get the same rise and fall shown in Figure 8L.3.  

Decoupling should be around .1μμμ { $\mu$ F (found from looking at the recommendations in the datasheet)

“How little hysteresis you can get away with” → how low of a threshold voltage at non-inverting input (V+V+V+ { $V_+$ ) is required to prevent the output from looking terrible. Pin 2 is still V+V+V+ { $V_+$  here. Instead of a 100k resistor, use one that is ~10x larger than the range of whatever potentiometer you use for this part.

Alternatively, you can use a resistor substitution box

Since we're using a slightly different part (the LM311N rather than the LM311), our circuit is better behaved than the manual assumes.

If you don't remove the connection between pins 5&6, you probably won't see any problems even without adjusting the potentiometer.

Skip the last question in this section: “Could you invent a way to diminish that lateness?”

To predict the oscillation frequency, you'll need to know how long it will take the capacitor to charge from the minimum voltage at V+V+V+ { $V_{+}$  to the maximum voltage at V+V+V+ { $V_{+}$ . When the non-inverting input (V+V+V+ { $V_+$ ) is at a higher voltage than the inverting input (V−V−V− { $V_-$ ), the comparator's output VoutVoutVout { $V_{out}$  will be set to -15 V When V+V+V+ { $V_+$  is at a lower voltage than V−V−V− { $V_-$ , VoutVoutVout { $V_{out}$  will instead be (approximately) +15 V From this, what are the maximum/minimum voltages that will be at V+V+V+ { $V_+$ ?  There is no current into the comparator's inputs, so you can treat the 100k and 10k resistor as a voltage divider. As the book notes, we can approximate the magnitude of the current through the capacitor CCC { $C$  as 15V/Rfeedback15V/Rfeedback15V/Rfeedback { $15 V / R_{feedback}$ , knowing this, what is the rate of change in voltage across the capacitor dVcapdtdVcapdtdVcapdt { $\dfrac{dV_{cap}}{dt}$ ? How long will it take the voltage at V−V−V− { $V_-$  to surpass V+V+V+ { $V_+$  in magnitude (i.e., how long will it take for the comparator to change states?) How does this time relate to the period of oscillation?

To find the feedback resistor for the Schmitt trigger oscillator, calculate how long it will take for VCVCVC { $V_C$  to increase from 1.8V to 2.7 V when the Schmitt trigger's output VoutVoutVout { $V_{out}$  is +5V.  The process should be similar to what you just did for the circuit in 8L.2. The assumption that the capacitor charges at a constant rate may lead to you over-estimating the resistance needed

Test for the same order of magnitude, unless you really want to do more math.

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misc pots and resistors