# VCO.MTH.4

Lesson Summary
Identify and compute Ohm’s Law.
Vocabulary
Electricity - The physical scientific processes related to the flow of electric charge.   Charge can be either positive or negative. The SI unit of electric charge is the coulomb C.

Conductor - A material that allows electricity to flow freely though it. Metals are great conductors, with copper being a commonly used conductor in electronics.

Insulator - A material that restricts the flow of electricity.  No material is a total insulator, common examples include glass and paper.

Current - The flow of electric charge.  The SI unit for measuring current is the ampere. Ampere, A,  is defined as the flow of charge across a surface at a rate of one coulomb per second.

Voltage  - The electrical potential difference between two points, denoted by a V. A single AA battery holds 1.5V

Resistor - An electronic component that restricts the flow of electrical current and voltage. Resistance of the material is measured in Ohm's signified by Ω. R1 = Resistor, R2 = Variable Resistor, R3 = Potentiometer.

Capacitor  - An electronic component that stores and discharges the flow of electrical current and voltage.  Capacitors use two layers of conductors, usually thin films of metal, aluminum foil or disks, separated by a polarized insulator made of glass, ceramic, plastic film, air, paper.   Capacitance is measured in farads, commonly displayed as micro farad or μF. C1 = Capacitor, C2 = Polarized Capacitor, C3 = Variable Capacitor.

Circuit -  A group of individual electronic components connected by conductive wires or traces which electric current can flow. The combination and order of components allow various tasks to be performed.

Ohm's Law - The current through a conductor between two points is directly proportional to the voltage across the two points. I is defined as the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. Exercise

Hear varying resistance of an applied voltage to the VCO EXP IN.

We will be supplying 5V+ to our VCO EXP IN from our Arduino through a  680kΩ resistor.  As we change resistor values we will be able to hear how current and voltage changes can alter our VCO settings.
Materials 1 x 680kΩ resistor 1 x 10kΩ Potentiometer 1 x Arduino Jumper Cables
Hardware

We will need to connect our Arduino and Werkstatt together in the configuration shown in Figure 1.   We will be starting with a 680kΩ resistor.  Once we have heard the change that 680kΩ provides try out other values to compare and contrast.  What happens to the sound with less resistance? What happens to the sound with more? Why do you think that is? Figure 1. 680kΩ  resistor

Here is a schematic overview of how voltage and current are related in our circuit. We can also swap our resistor for a potentiometer. Potentiometers offer a variable resistance so we can hear the changes as we turn the knob.

Figure 2. Potentiometer

Software

For our ohms law exercise we will be using an Arduino to speak to the program Processing.  The Arduino should already have the Standard Firmata sketch uploaded to it. For more detailed information on the Arduino uploading process visit their website

Open the Ohms_Law.pde program, ensure all connections are similar to Figure 1 or 2 and click the run button.  This program alternates between sending 5Vs+ out of our Arduino, and sending no voltage at all.  This oscillation will allow us to compare the differences.  Change resistor values and hear the differences as voltage is changed.

For a more detailed walkthrough of the program refer to the comments in Figure 3. Figure 3. Screen capture Processing is an open source programming environment and community.

moog_werkstatt processing_files.zip

The Arduino is a micro controller and programming environment for interactive systems.

Standard_Firmata.zip

Practice

The Werkstatt has a 12VDC power input source and accepts 1.2 Amps from the power converter. What is its overall resistance?

The resistance of dry human skin is about 500,000 Ω while sweaty human skin is about 1000 Ω. How much current passes across someone’s fingers if they touch the 5V output on the Werkstatt when their skin is wet and dry?

A stereo speaker has a resistance of 8.00 Ω. When it is operating at full power (exactly 100 watts) it uses 35 volts of electricity. What is the current drawn by the speaker?

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