{"id":2274,"date":"2022-02-15T21:15:49","date_gmt":"2022-02-16T02:15:49","guid":{"rendered":"https:\/\/courses.ideate.cmu.edu\/48-339\/s2022\/?p=2274"},"modified":"2022-02-15T23:39:16","modified_gmt":"2022-02-16T04:39:16","slug":"class-notes-15-feb-2022","status":"publish","type":"post","link":"https:\/\/courses.ideate.cmu.edu\/48-339\/s2022\/?p=2274","title":{"rendered":"Class Notes, 15 Feb, 2022"},"content":{"rendered":"

Note: Office hours on Tuesday, no Thursday<\/p>\n

Intro to Electricity and Power<\/strong><\/h2>\n

Start with example using light and power<\/h3>\n

100w incandescent bulb<\/p>\n

23w LED bulb<\/p>\n

120v 20a electrical circuit<\/p>\n

wattage \u2014 what does it really mean?\u00a0 Is a 100W incandescent bulb brighter than a 23W LED?<\/p>\n

Compute amps based on wattage and 120v power.<\/p>\n

Same brightness but different amounts of power, meaning LEDs are more efficient:<\/p>\n

100W incandescent bulb ~1A<\/p>\n

24W LED bulb ~0.2A<\/p>\n

 <\/p>\n

How things move<\/h3>\n

Think about power in the physical world:<\/p>\n

voltage => weight<\/p>\n

amps => speed<\/p>\n

I weigh 85 kilos, how “dangerous” am I if I bump in to you while I’m walking?\u00a0 While I’m running?<\/p>\n

Is voltage dangerous or is amperage dangerous?<\/p>\n

Bicycles vs. cars. Hit by a car or a bike at 10mph, which is worse? Is it really voltage or amps?<\/p>\n

Handheld 50 KW stun gun.\u00a0 500 times as strong as strong as a 100W light bulb.\u00a0 Why doesn’t it kill people?<\/p>\n

Think about volts vs. amps.\u00a0 Where does the power come from?<\/p>\n

Mine uses two 9V batteries, the ones you use in consumer electronics. \u00a0 50KW is more like 50KV at 1 Amp, or 100Kv at 0.5 Amps.<\/p>\n

Where we get power<\/h3>\n

A\/C wall power to drive power supplies (PSUs).<\/p>\n

DC power from a PSU, from 5V to 12V, we use 6V in class.<\/p>\n

USB power converted by Arduinos or other devices<\/p>\n

Arduino pins only have a tiny amount of power: 5V at 20 mA (milliamp).<\/p>\n

How motors work<\/h3>\n

How to determine power requirements<\/p>\n

How to drive servos vs. DC motors<\/p>\n

Spring-loaded solenoids that require constant power to stay open\/closed<\/p>\n

How do you lock a motor and prevent it from turning?<\/p>\n

What happens if you spin a DC motor?\u00a0 It’s now a DC generator and could fry your Arduino.\u00a0 We “fix” this using diodes in the circuits.<\/p>\n

For moving things, use basic physics<\/p>\n