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Lab 8/9 Mar 19 / 21 by Mind Map: Lab 8/9 Mar 19 / 21
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Lab 8/9 Mar 19 / 21

General plan

Explore and "finish" the grounding issue in last part of lab 7

Begin lab 8 "Transistor Circuits" (old name Lab 4)


A. Finish / understand last lab, especially grounding issues

1. Read email describing what Maria discovered about grounding issue

2. Re-build full-wave bridge (Step VIII) and confirm that it works well IF the grounding problem with digital oscilloscope is dealt with, We only have one analog scope (which we can share) (You can work together in pairs), OR: Are there other ways of dealing with the grounding problem? DAQ card w/ your DAQ software? I like this idea, but not sure if DAQ ground will conflict

B. Begin Lab 8/9, instructions are on github, although labeled "lab 4" in prior years

Download Lab 8 instructions from github, Address:

I. Transistors (2N3904) as Diodes, You should spend a lot of time on this section. The lab manual suggests just using a multimeter, but what other things can you do to investigate it's diode properties?, Using the multimeter to measure resistance, you can deduce whether it is an npn or pnp transistor. you can then verify this from the 2N3904 wikipedia article, Half-wave rectification?, When I tried this, it sort of worked in the BC configuration, but not in the EB configuration (using half-wave rectification circuit from last lab), I may have fried the transistor doing this! Looking at the data sheet for 2N3904 (see github), the maximum base-emitter voltage is 6 volts. So, to test wave rectification, do not use the 15 V AC!, I don't know whether I "fried" the transistor doing this, Using a lower voltage, half-wave rectification works in both orientations. (Use a separate function generator, not the Heathkit)

II. Transistors as switches, Falstad simulation, There is a +5V connection on the Heathkit to the right of the breadboard. There is a ground connection (arrow pointing down) on the left side of the breadboard., Really do what the instructions say! Measure currents and voltages where you can., "Why the 10K resistor?", I don't want to answer the question for you. I discovered the problem when I was using my own hand to connect the switch to +5V. --> Sometimes the LED would turn on a bit, even when I didn't have the +5V connected., I get about 10 or 12 milliamps going through the LED

Simulation / resources




Switch simulation (part II)

Wikipedia article on transistors

2N3904 Wikipedia article

Data sheet on github

C (Lab 9)

We are going to branch off from Part II of last week's lab "transistors as switches" -- What is the point of using the transistor as a switch?

This activity will be thin on instructions because you can figure out how to do it and learn while doing it

GOAL: Use LabVIEW + DAQ board (digital output) and a modification of the circuit in part II to turn the LED on and off using a LabVIEW program

Find the example program XDOUT.VI, This is an example program from Measurement Computing that lets you set the digital output channels using front panel buttons. You will need to look at the instruction manual to figure out which pins are which

Wire things up so you can turn the LED on and off using LabVIEW (this should take you 1 to 2 hours to get to this point)

Once it is working, use a multimeter to measure the current going through the LED. Also measure the current going into the base when the switch is on / off. Don't just measure, but think about the numbers you're getting

No bonus points, but if you're a bad-ass

Use the oscilloscope to measure how long it takes the transistor to switch, once you change the base voltage from 0 to 5 volts, You will need to figure out how to look at the switching voltage and some kind of voltage that represents the collector / emitter current, You'll need to use both channels of the oscilloscope, Trigger off of the rising edge of the logic signal (the switching voltage) and measure the time delay for the collector/emitter current to rise

Look at the instruction manual for the 2N3904...what is the rise time supposed to be???