CS-4540 Robotics Lab 00 - Introduction and OHM's law

Goals Robotics these days encompasses a very wide range of definitions. Everything from factory manipulator arms to autonomous cars to voice controlled door locks. Jose is going to walk you through the high end of kinematics and dynamics theory. My plan is to work the other end of the spectrum and give you some skills for dealing with the basic technologies used in these systems. I feel that a basic understanding of digital electronics will come in handy when working with small personal robots as well as larger robotic systems. Some of the senior design groups are dealing with this. Their projects are working with IoT (Internet of Things) devices and systems. The teams end up spending half their time learning how to connect electronic modules together before they can even start to write control systems for them.

Projects My end goal for this class is to have you building and programming small robotic systems and IoT projects. As for specific projects I am still making that up as I go along. Much of it depends on what kind of equipment I can scrounge up or get the department to purchase. These will include small wheeled and treaded robot motion bases, repurposed Roombas, servo controlled arms, and assorted sensors and motion control system elements.

Tech To get there we will be starting with basic electrical circuits. This includes an understanding of the elements that make up a circuit, how to represent a circuit using schematic diagrams. How to utilize Ohm's law (Georg Ohm, German physicist, 1827) to calculate the relationship between resistance, voltage, and current. How to use the power law formula to calculate the energy your system is going to need and spec out the sources you can use to power it. We will build on this to work with some basic digital circuits. How to drive LED's and motors. How digital logic works and the difference between 5 volt logic levels and 3.3 volt logic levels, as well as how to covert between them. On the web see: https://en.wikipedia.org/wiki/Ohm's_law

Arduino Next will be working with the Arduino micro controller boards. Connecting them to various input and output modules. How to program them in C and what kind of limits will your programs have to deal with. We will also be going over various communication protocols such as IIC that are used for networking more advanced interface modules together.

Raspberry Pi The last major component I want to cover will be using the Raspberry Pi. How to program on it and how to interface with it's General Purpose Input Output interface (GPIO). The Pi uses 3.3 volt logic where as many interface modules use 5 volt logic. We will be reviewing how to interface these two systems to try to avoid burning anything out. These various systems will be used by your teams during the rest of the semester for the construction of one or more small projects (depending on the complexity).

Basic Electrical Circuit The flashlight is a prime example of a basic electrical circuit. It consists of three of the main elements that make up just about all electrical systems: Power source (batteries) Control system (switch) Load (light bulb)

Conventions It is called an electrical "circuit" because for an electricity to do work requires the flow of electrons from one pole or terminal of a voltage source to the other through a conductive path. There is potential confusion when it comes to references you may run across as to the direction current flows through a circuit. Conventional current flow is modeled as going from the positive to negative terminals. Electron current flow is more accurate description as it has the current flowing from the negative to positive terminal. I'm going to use the electron flow convention.

Schematic To avoid having to draw pictures of batteries and light bulbs to communicate about electrical circuits we use schematic diagrams.

Even more generalized The battery symbol is replaced with a general purpose voltage source symbol, the light bulb is replaced with an symbol for a resistive load (resistor), and the switch has been removed because we are going to assume for the moment that our circuit is always on. This gives us a really simple system to explore the electrical properties of a circuit.

Circuit perimeters Georg Simon Ohm I = current flow measured in Amps (A) Voltage is measured in Volts (V) {or sometimes E} R = Resistance is measured in Ohm's (Ω) François-Marie Arouet (Voltaire) André-Marie Ampère

Ohms Law * 𝑉=𝐼 ∗𝑅 The three values that describe circuit dynamics are: Volts (electrical pressure driving the flow of current) Amps (the measure of the quantity of current flow) Resistance (the impedance resisting the flow of current) These three values always relate to each other in a circuit. Change any one of them and the others will change appropriately. This behavior can be modeled mathematically with a simple algebraic formula called Ohm's law. 𝑉=𝐼 ∗𝑅

Examples Given: R = 10 Ω and I = 3 Amps, what is the Voltage? V = I * R V = 10 Ω * 3 A V = 30 Volts Given: V = 5 V and I = 0.03 Amps, what is the Resistance? V = I * R => R = V / I R = 5 / 0.03 R = 166.7 Ω

Digital Multi-Meter To put this into use and work with these circuit elements will require some way to measure these values in working circuits. For this we will be using a tool called a Digital Multi Meter (DMM). {They are also commonly referred to DVM's (Digital Volt Meter)} Depending on the particular model it can directly measure voltage, resistance, and current, as well as a few other values that will be handy later such as frequency and duty cycle. The model shown here is auto ranging so that it will automatically adjust the displayed value to be in range of what you are measuring.

Resistors Although the load resistance in our schematic diagram up till now has represented a general circuit element that will draw current, there is a simple electrical component called a 'resistor' which is used to resist current flow. They come in many physical packages, but the ones that we will be using look similar to this: We have been using this symbol to represent a resistor in our circuits: In older schematics you may fine it represented as such:

Measuring resistance with the DMM

Resistor color code Instead of having to measure every resistor to find it's value before we use it, they are labeled with their resistance using a system of colored bands.

Resistance measurement examples Live Demo

Voltage Measurement Live Demo

Current Measurement Live Demo