A man named Thevenin once had a good idea. This idea was that If you had any collection of resistors, batteries, and diodes hidden in a box, one could replace it with a single batters and resistor, and the two would be indistinguishable, as far as voltage, current and resistance go, I'm sure the complex one would be heavier ;). I drew up a little diagram in gimp to demonstrate this. So basically, you can replace any complex circuit with it's "Thevinin equivalent". And that was the topic of lab on Feb 5th.Lab/Question for "Friday Feb 2nd": To test Thevinin, we used a LEGO motor. (Note dates may not match)
Fell the torque of the motor with a batterypack versus the logo-chip.
. The power from logo-chip is much weaker than the batterys.
⌘ Use an oscilloscope to monitor the change in the voltage p between the power and ground busses as you connect and disconnect a 47 ohm resistor between the busses. Based on your observations, (approximately) what is the Thevenin equivalent circuit for your battery pack?
. Vth = 4.5V Rth = ~0
⌘ Use PicoBlocks to set one of the LogoChip output pins “high”. Use an oscilloscope to monitor the change in the voltage between this pin and ground as you connect and disconnect a 47 ohm resistor. Based on your observations, (approximately) what is the Thevenin equivalent circuit for the LogoChip output pin?
. Vth = 4.1V Rth = 11.4
⌘ Based on your observations above and perhaps additional experiments, determine the Thevenin equivalent circuit for a non-spinning3 LEGO motor. How much current really flows into a motor driven by LogoChip pin?
. [Motor and battery] Vth = 4.5V Rth = 21. I[Logo] = Vlogo / (Rlogo + Rmotor) = 0.12 A
Lab 1-4 in the Student Manual:
. Vin = 4.5; Vout = 2.2; Isc = 0.43mA; Vth = 2.2V; Rth = 5.1k
"Tuesday Feb 5th":
Lab 1-5 in the Student Manual (More with the digital oscilloscopes)
. Rise time of SquareWave =35 ns
Lab 1-6 in the Student Manual (AC Voltage Divider, experimentally)
. Vin = 200 mV Vout = 100 mV
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