Session 3 - Friday, February 7

More with the Digital Oscilloscopes - Lab 1-5 in the Student Manual

The first thing we did in this lab session is to familiarize ourselves with the digital oscilloscopes and function generator. We practiced using the VOLTS/DIV and SEC/DIV knobs which control the number of volts or time, respectively, displayed per division. We also greatly practiced using the TRIGGER controls, which were very difficult, but with some help about how you can't trigger when the oscilloscope is in scanning mode.

As a practice exercise we used the different settings of the digital oscilloscope to measure the "risetime" of a square wave from the function generator to be 20 ns. During this practice exercise we also learned that the SYNC connector always puts out a square wave whose rise and fall "syncs" with that of the sine wave function. One other setting we practiced with was the difference between AC and DC coupling on the oscilloscope.

One final exercise we used to practice these new skills was to make an accurate measurement of the frequency output by the function generator. We did this by setting the function generator to generate 100kHz pulses. We then used the oscilloscope to measure the period to be 10 microseconds. Using the relationship of 1/f = T and 1/T = f, this measurement confirms that the frequency is 100kHz, showing that we can make very accurate frequency measurements using the oscilloscope.

AC Voltage Divider, Experimentally - Lab 1-6 in the Student Manual

In order to connect our new knowledge of the function generator and the digital oscilloscope with our previous knowledge of voltage dividers, we spent some time considering the question of how a voltage divider would act when connected to an input voltage that changes with time, specifically a 1kHz sine wave.

Another Good Idea: The Transistor

After learning the theory behind transistors and MOSFET transistors in particular, we took our old familiar LEGO Motor circuit and added an IRL 510 transistor. The Arduino chip had no difficulty with running the motor when the transistor is connected such that the G channel is tied to the output pin, and D channel is connected to the motor which is connected to the 5V pin, and the S channel is tied to the ground. The torque it took to stall the motor appears to be the same as when the transistor is not in the circuit.

We next added a 9V battery to give our motor an even better power source. Of course, we did this very carefully since accidentally connected this battery to the Arduino would fry  the whole Arduino chip. We again used the Arduino to control the circuit via the transistor and output pin and it had no difficulty doing so. Of course, since we greatly increased the voltage of the power source the torque needed to stall the motor is now much greater.

This lab is very important as it shows how we can use a complicated and delicate controller like the Arduino to control heavier-duty circuits that need more power than can be provided by the Arduino itself by utilizing the power of transistors.


(I'm having trouble getting the videos to upload as the Internet keeps cutting in and out and I will try again later. I will also add some more details related to the videos then.)