RC Time Constants and Oscillators

• time constant
  • download or create the following circuit on Multisim (if creating do the following)
    • change the default instrument settings as described in Bugs 'N' Stuff
    • set the oscilloscope to an appropriate setting, start with time base 1s/Div and Channel A scale 5 V/Div.

• examine the oscilloscope trace (use alt + print screen key then paste onto document)

• perform the following analysis
  • calculate the RC time constant T=R*C
  • set cursor 1 to the beginning of the decay, set cursor 2 to a point about 36.8% of the decay (i.e. 3.7 Volts)(note this is 1/e)
  • read the time for the decay from T2-T1 on the screen
  • compare time shown to time constant
• repeat for charging the capacitor except place cursor 1 to the start of the charge and cursor 2 to about 63.2 % of full voltage (i.e. 6.3 Volts).(note this is 1-1/e)
• As a bonus change the capacitor and resistor values. Complete a charge or discharge and compare to the RC time constant. Change them enough that you will have to adjust the timebase scale.
• What to hand in

 

• Definitions some circuits which could be based on RC time constants
  • A monostable circuit is a circuit which will supply a fixed length of pulse (one oscillation) and then stop.
    • An application of a monostable circuit could be a debounced switch.
  • An astable circuit continually oscillates. An example of this circuit is the 555 timer project.