Lab 2.2 Ohm s Law and Introduction to Arduinos Objectives: Get experience using an Arduino Learn to use a multimeter to measure Potential units of volts (V) Current units of amps (A) Resistance units of Ohms (Ω) Learn Ohm s Law through discovery based learning What you need for this lab: From Arduino Kit: 2 different resistors, breadboard, RedBoard (or UNO), USB cable, LEDs, jumper wires Multimeter Laptop Microcontrollers A microcontroller is a "brain" of a mechatronic system that interfaces sensors with a computer. Microcontrollers can: perform math operations take sensor readings monitor analog and digital inputs control analog and digital outputs like lights, sounds, and motors. Arduino-compatibile microcontrollers are easy to use for those with no previous electronics experience inexpensive cross-platform open source programmed using a free Integrated Development Environment (IDE) that is compatible with Windows, Mac OS, and Linux. Searching the web you can find a multitude of Arduino projects: robotics, smart devices, and musical devices. There are many types of Arduinos; we will be using an Uno or an Uno compatible board manufactured by Sparkfun called the Redboard. Page 1 of 6
Breadboards A solderless breadboard is a great tool for making temporary circuits and prototyping without soldering. Our breadboards have horizontally connected rows, and power rails that run vertically along the sides. Pictured is the front and back of a breadboard with the backing removed so you can see the connections between the horizontal rows and the power rails. Typically the (+) power rail is connected to power in your board and the (-) power rail to ground (GND). Horizontal rows are separated by a ravine, so the left and right side of each row is not connected. Notice the left power rails are not connected to the right power rails. The numbers and letters marked on various rows and columns don t serve any purpose other than to help guide you when building your circuit. Task 1. Decode Resistor Color Codes and Measure Resistance: The electrical resistance of an object is a measure of its opposition to the passage of an electric current. The symbol for a resistor is shown at the right and units are Ohms (Ω). Choose two different resistors from your Arduino Kit and calculate their resistance using the chart. Resistor 1 Resistor 2 Colorband resistance (Ω) Measured resistance (Ω) Check your calculations using the multimeter. Set the multimeter to Ω. If you use a high resistance resistor (e.g. >100 kω resistor) be sure to wrap the wires around the leads and not use your fingers/body in the circuit. Note that to measure resistance using a multimeter the component must be removed from the circuit. Page 2 of 6
Task 2. Power up your Arduino Board and Measure Voltage: The voltage between two points is the electrical force that would drive an electric current between those points. The symbol for voltage (battery) is shown at the right and the units are Volts (V). Measuring Voltage on the Arduino Board: The Arduino is usually powered from the USB port on a laptop. You can also use an external power supply such as a battery pack or a wall wart. Plug the USB cable into your Arduino board and the other end into your laptop. Connect one jumper wire (any color) from your 5 Volt channel on your Arduino to your + positive power rail Use another wire to connect the GND on your Arduino to the negative power rail. Connect a wire from your + power rail to one row (shown as a red wire here to the top row). Connect a wire from your - power rail to two rows below. (also shown as black here) Use your multimeter to measure voltage. Select Volts on your multimeter. Pull the wires upward slightly so you can see the conducting pins. Hold the red and black leads of the multimeter onto the ends of each pin. Voltage Task 3. Measure Current and Discover Ohm s Law: Select two different resistors. To measure current your multimeter needs to be in line with the circuit, acting as a wire in the circuit. Set up the circuit as shown at the right with one of your resistors. Cut the circuit by leaving one end of the resistor unconnected. Connect the free end of the resistor to one of the leads of the mulitmeter. Hold the other multimeter lead on the pin of the other (red) wire to complete the circuit. Current is measured in Amperes (A) or amps for short. Switch the multimeter to ma (milliamps). Record the multimeter current reading in the Table. Switch resistors and measure the current for the other resistor. Complete the table. The voltage is the voltage provided by your laptop 5 Volts. Record your values in amps, not milliamps. Resistance Ω Voltage (V) Current (A) V/R Calculate the ratio of the voltage to the resistance, and record in the last column of the table. Compare the third column to the fourth column of the table. Based on this comparison, can you determine a relationship between the voltage, current, and resistance? This is Ohm s Law. Write it in the box. OHMS LAW Page 3 of 6
Task 4. Build 3 circuits. A single LED circuit, two LEDs wired in parallel, and two LEDs wired in series An LED is a Light Emitting Diode. Diodes allow current flow only in one direction. The long lead of the LED is the positive side of the device. Most electronic components are diodes with a positive side labeled. Diodes won t work if they are reversed. Wire your circuits properly. You need a resistance of at least 140 ohms in your circuit to prevent LEDs from burning up. Using the circuit from the previous task, connect the loose end of your resistor to the middle row as shown in the fritzing diagram. Hook up a single LED to complete the circuit (long leg to + power in the top row, short leg to power in the middle row). Note the brightness. Sketch the connections that you made in the form of a circuit diagram using the standard symbols shown below. Add a second LED so both LEDs are on, in such a way that if one of the LEDs is removed the other LED stays on. Once you have achieved success, sketch the connections that you made in the form of a circuit diagram. Is your original LED the same brightness, or was it brighter or dimmer that it was? Can you explain any differences in the brightness, if any? If one of the LEDs is removed, why does the other LED stay on? If you could characterize the light bulbs as being in series or parallel circuit, which would it be? Devise another way of connecting two lights into the same circuit, where if one LED is removed, both go out. Sketch the circuit diagram. Is your original LED the same brightness, or was it brighter or dimmer that it was? Can you explain any differences in the brightness, or the fact that it is the same? If one of the LEDs is removed, why does the other LED turn off? If you could characterize the light bulbs as being in series or parallel circuit, which would it be? Upload a photo of your circuit diagrams and a photo of a working Arduino circuit with 2 lit LEDs to your drop box to obtain credit for this lab. Page 4 of 6
Task 5: Get the Arduino IDE for next lab Download the Arduino IDE from this website: https://www.arduino.cc/en/main/software Scroll down to Download the Arduino IDE and select your operating system from the choices. Install the Arduino IDE. Restart your computer and open the Arduino environment (the blue Infinity symbol with the positive and negative symbols in the center.) If all went well you should see an editor window like this: Navigate to the Boards manager by going Tools - Board Board Manager. Select Uno. Check to ensure you have the correct drivers to connect your laptop to your board. Plug the usb cable into your Board and the other end into your laptop. From the tools menu, select port. In windows look for a com port numbered above 3. For Mac it will be a /dev/cu.usbserialxxxxx(some hex #) Depending on your operating system, you may need to install additional drivers. https://learn.sparkfun.com/tutorials/how-to-install-ftdi-drivers http://www.ftdichip.com/drivers/vcp.htm If there is any remaining time, work on your team project Page 5 of 6
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