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CWNC TROJANATORS ELECTRICAL BASICS 09/28/2016 ELECTRICAL 101 • Types of Electrical Current Delivery in Circuits and Loads – AC • Wall power in USA: 120VAC • High Voltage Power Transmission: 100,000 Volts • Current “alternates” in the wire- it literally changes direction periodically • Examples of AC signals: Electric Guitar; the pickup responds to vibrating string by producing an AC voltage ELECTRICAL 101 • Types of Electrical Current Delivery in Circuits and Loads – DC • Car Battery: 12VDC, AA Battery: 1.5VDC, Modern iPhone/ Android Battery: 3.7VDC • Microelectronics: Microcontrollers, Transistors, etc. typically 3.3VDC to 5VDC ELECTRICAL 101 • Battery Symbol RESISTANCE • Just like a skinny vs fat garden hose will change the RATE of water flowing out of it for a given water pressure, we can change the amount of current along a circuit by adding a RESISTANCE factor. This component is called a RESISTOR • SYMBOL • UNIT: OHMS (after German physicist Georg Simon Ohm • Ohm’s Law: VOLTAGE = CURRENT * RESISTANCE • Voltage is like a pressure, think of a water tank connected to a hose handle VOLTAGE AND PRESSURE VOLTAGE DIVIDER • I need to track a 12VDC battery voltage on an analog pin on a microcontroller. I am trying to see what the current level the battery is. The microcontroller has a maximum rated input of 5VDC. How can I go from 48VDC to 5VDC so I don’t blow up the microcontroller? – Voltage Divider: a simple way to shift the voltage from one level to another • Need to watch the load current because if it’s too high, the output of the voltage divide will SAG, which is a technical term for dropout, lower, cut out, drag, dip… VOLTAGE DIVIDER SOLUTION • Atmel ATMEGA328 (popular on Arduino boards) has an input resistance of at least 10Kohms DC. • We can set R2 to 1,000 ohms. This will not “load” the output voltage considerably • Knowns:Vin, R2,Vout. • Rearrange the equation and solve for R1 – R1 = R2 (Vin – Vout) / Vout • R1 = 1,400 Ohms. • Total Resistance from 12VDC to “ground” = 1,400 + 1,000 = 2,400 Ohms • Total power loss = Pwatts = V^2 /R = 12*12 / 2,400 = 0.06 watts = 60 mWatts • Total current in resistors from V = I*R; Solve for I; – I = V/R = 12 / 2,400 = 0.005 AMPS, = 5 milliAmps DC RESISTANCE PER FOOT, COPPER NICE CHASSIS WIRING UGLY CHASSIS WIRING COMPONENTS • The RoboRIO is the brain of your robot. The RoboRIO breaks out all of the connections you will need to operate your robot with and gives you the option of programming your robot in three different languages, Java, C++, and LabView. The RoboRIO specifications are as follows: Xilinx z-7020 CPU with a Dual Core ARM Cortex A-9 processor and FPGA combination • 256MB DDR3 RAM • 512MB nonvolatile storage(for programs) • 2 Host USB ports (For cameras and other external USB hardware) • 1 10/100BaseT Ethernet connection(for robot communication) • Up to 8 Analog Inputs(4 on Analog In Header/ 4 on Expansion Port) • 2 Analog Outputs(on the Expansion Port) • Up to 16 Digital IO ports(10 on DIO Header/ 6 on Expansion Port) • 10 Pulse Width Modulation(PWM) Ports(for motor control) • 4 Relay Ports(for directional motor control) • Other communication types available including RS232, I2C, SPI, and CAN