Lab 6: Transistor Switching

In this lab we worked with transistors and built circuits using them.  Transistors are like a switch but instead of just a simple on/off, they can switch the flow of electricity.  In this first circuit we built, the transistor is "turned on" by a push button which allows the flow of electricity to the base.  This flow of electricity to the base is what switches the transistor to allow current to flow through it.

Here, I'm pushing the button which is turning on the transistor, which then allows the current to pass through and turn on the LED.



In this next part, we removed the push button switch and resistor #2 and replaced it with our fingers.  Since our bodies have high resistance, they act similar to the small resistor components.

Here, I'm bridging the connection between the wires with my fingers and current is flowing through my body.


Next we set up a circuit with a 100k potentiometer and resistors and used our 5V power supply.  An Ammeter was used to measure the current passing through different points in the circuit, before or after resistors and the transistor.

Here, the ammeter is registering the change in current as I am adjusting the potentiometer.  The Beta (Gain) of our transistor was determined to be 220.  The current was also determined to saturate at 13mA.


Lab 6 finished!

Lab 5: Switches And Relays

In this lab we learned about and experimented with switches and relays.  Switches can have multiple poles and multiple throw positions.  They are a good way to turn power on and off to the circuit without having to disconnect any components.  Relays use a low voltage or small current to flip between positions.  They are also categorized like switches in that they can be SPST, SPDT, DPST, DPDT, etc.  There is an iron core in the relay with a coil of wire wrapped around it.  When there is current flowing, a magnetic field forms around the iron core and pushes or pulls a lever (springy strip of metal).


After understanding how switches and relays work within circuits, we went ahead and build a circuit that included a push button switch, a DPDT relay, 2 LED's, connecting wires and a 5V power supply all connected using the solderless breadboard.  We ran the power through the relay so that the relay was switching on and off by itself when the pushbutton switch was pushed.  It looked like only one of the LED's was lit because the other one was flashing to fast to see it from the relay switching itself on and off.

You can see that the LED that lights up is controlled by the pushbutton switch.  The switch controls the current to the relay and when current is turned on or off, the relay powers one or the other LED's.



Capacitors act like batteries in a circuit in that they can be charged up and store energy.  Alignment is important when placing capacitors in a circuit.  The long wire needs to be connected to the positive side of the circuit otherwise the capacitor won't work.


A capacitor was introduced to the circuit by attaching the short lead of the capacitor to the negative side of the circuit.  We placed the leads of the capacitor on either side of the relay coil (bottom left and right pins) in the breadboard.  The capacitor charges when the current flows and when the contacts of the relay open, the capacitor acts like a battery and then sends power to the relay.  This cycle repeats over and over which causes the LED's to flash!

Lab 5 finished!

Lab 4: Schematics, Ohm's Law And Potentiometers

In this lab, we learned about schematics, using Ohm's Law (voltage, current, resistance), and potentiometers.  Schematics are a good way to show how a circuit works.  It's essentially a road map of the current path and the stops along the way are any number of electrical components (capacitors, resistors, LED's, relays, potentiometers, etc).



First I got 3 LED's and 3 different resistors (100ohm, 1.0Kohm, 10Kohm).  Then I constructed 3 different circuits, each using one LED and one of the resistors.  As expected, the resistor with the lowest rated resistance produced the brightest light from the LED.

The 100ohm resistor is at the top, then the 1.0Kohm resistor, and the 10K resistor is on the bottom.  You can see that less resistance means higher current based on Ohm's Law.  Since V=IR, if the resistance goes down then the current (I) must go up to satisfy the equation.



To test this even further, I hooked up an LED circuit with no resistance (a wire) to the power supply in the breadboard.  Based on Ohm's Law, since there is no resistance, the current will be very high and possibly damage the LED.

When the power supply was plugged in, the LED didn't explode but instead emitted a dull steady flash.  This was determined to be a safety feature in the power supply that was keeping the full current from running through the circuit and destroying components.



Next we learned more about Ohm's Law and KVL and studied examples.  By noticing the relationship between voltage, current and resistance, we calculated the resistor that would produce the brightest LED without damaging it and staying within the LED's tolerances.  Since the LED uses 1.85V and we're working with a 5V power supply, the resistor needs to take 3.15V.  Using Ohm's Law, the resistance for the circuit should be 105ohms.  I got the resistor that was closest to this number (100ohm resistor) and connected the circuit to the breadboard.

You can see that the LED is very bright when connected to the 100ohm resistor.



Potentiometers are adjustable resistors.  There are many different potentiometers, each with a different rating.  If a potentiometer is connected to a circuit with a resistor also in the circuit, the resistance of the resistor is always added to whatever resistance is dialed into the potentiometer.

Here you can see that when I use the tool to manually adjust the potentiometer, the resistance is also being adjusted.  With adjusted resistance comes adjusted current which leads to varying degrees of brightness.




Finally we connected a LDR (Light Detecting Resistor) in a circuit with the LED and 5V power supply.  The LDR changes it's resistance based on the amount of light that reaches it.  Once the circuit was assembled, the LED was bright.  We covered the LDR and noticed the change in brightness of the LED caused by the change in resistance.

Here you can see that when the LDR is covered up, the resistance goes up and the current goes down to keep the Ohm's Law equation balanced which dims the LED.


Lab 4 finished!

Lab 3: Using A Multimeter

In this lab, we learned how to use a multimeter to test continuity, resistance and voltage.  The multimeter has many more functions but these are the functions we experimented with in the lab.


Continuity is tested by turning the multimeter switch to the icon that looks like a soundwave.  I used the probes to test continuity between paths on the circuit board I worked on in Lab 1.  The multimeter sends a small voltage through the probes and if the voltage comes through the circuit and back to the multimeter, the multimeter beeps and there is continuity.  The paths that were connected had continuity.


Next I tested the voltage of a 1.5V AA battery by adjusting the multimeter to 2V in the DC range.  The 1.5V battery read 1.449V which was only slightly less than the rating.


The 9V battery was then measured by the same process of connecting the probes of the multimeter to the positive and negative ends of the battery.  The 9V battery read 8.152V which was less than the 9V rating meaning it had been used a bit and lost some of it's charge since it was new.


It was also important to keep in mind that the multimeter has AC and DC modes when measuring voltage and you have to switch between the two when testing each one.  If not, your voltage reading will be 0.


We then tested the resistance of 5 resistors.  The value of the resistors was determined from the colored bands around the resistors.  The last color in the first 3 or 4 is a multiplier which tells you how many zeros to add.  The final color give you the tolerance of the component.  The 5 resistors I chose had a value of .68Kohms, 2.70Kohms, 470ohms, 100ohms, 1.00Kohms.  All the resistors had their resistance measured by the multimeter and touching the probes in any order on the ends of the resistor.  All five were very close to their rated resistance.


A potentiometer was tested next.  Potentiometers are resistors that can be adjusted.  I connected the multimeter across two adjacent pins and lowered the potentiometer as far as it would go and the reading was 0.8ohms.  Then I raised the potentiometer as far as I could and the multimeter read 9.76Kohms.  We were also able to tell if the potentiometer was linear by adjusting it to roughly half way and checking to see if the resistance was also roughly halfway between 0 and 10K.  The multimeter read 4.83Kohms which confirmed that the potentiometer was in fact linear.


The LDR (Light Dependent Resistor) was also tested.  By covering up the resistor, the resistance changes due to the change in light.  The max resistance I was able to achieve by covering the LDR was 0.515Mohms.


A similar procedure was followed when measuring a pressure dependent resistor.  After connecting to the multimeter, applying pressure to the resistor registered a change in the resistance.  The resting resistance without applying pressure was 350ohms.


The temperature dependent resistors were also tested in a similar fashion.  Once connected to the multimeter to measure resistance, I held the thermistor in my hand and noticed the increase in resistance.  My classmate also held the thermistor and since her hands were colder than mine, we were able to notice the difference in the two resistances based on the different temperature applied.

Lab 3 finished!

Lab 2: Introduction To Using A Breadboard

In this lab we practiced building a circuit on a solderless breadboard.  The solderless breadboard is an easy way to experiment with different circuit configurations because you can instantly attach and disconnect components at will without using any solder or connectors.  The breadboard has metal strips that connect columns and rows of holes together.  The metal strips are springy so when a solid-core (not stranded) wire is inserted, the metal strip grabs hold of the wire.



We used an LED and a 1.0K ohm resistor, along with our 5V power supply to practice constructing a circuit on a breadboard.  Here is the assembled circuit with LED lit up.

The LED is lit up and not exploding because the resistor is in the circuit.  The positive and negative leads of the power supply are going into the positive and negative rails of the breadboard.

Lab 2 finished!

Lab 1: Introduction To Soldering And Making Your 5V Power Supply

In this first lab, we completed two main tasks.  We first learned the proper way to solder electronics by instructor explanation and watching videos.  Then we practiced soldering random components on a small circuit board.  I used the techniques we had just learned and soldered five components onto the circuit board.  Having soldered before when changing out electric guitar pickups, the soldering of electronic components to a circuit board was fairly easy.

You can see I placed the components in random positions on the circuit board.

This picture of the back shows that the solder is completely covering the copper contact and the wires have been clipped.



The second task we needed to complete in the lab was to make our own 5V power supply.  To practice for this, I soldered 2 wires together.

These were two small scrap pieces of wire but the technique would be the same when making the power supply so it was good practice.  After being sure to heat both wires with the soldering iron, the solder was sucked into both wires and created a strong connection.



Now, we used this technique in making our power supply.  I exposed the wires and stripped them, determined the polarity and soldered the red lead to the positive and black lead to the negative.  Finally I applied heat shrink tubing to the connections for protection from shorting out the power supply.

The heat shrink tubing is completely covering the soldered connections.

Lab 1 finished!