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Build an Electronic Night Light

Build an Electronic Night Light. Electrical and Computer Engineering, Northeastern University. About how many electrons are in a short wire?. What Do Electrical Engineers Do?.

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Build an Electronic Night Light

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  1. Build an Electronic Night Light Electrical and Computer Engineering, Northeastern University

  2. About how many electrons are in a short wire? What Do Electrical Engineers Do? • Design computers, cell phones, MP3 players, plasma TVs, electrical power systems, satellite communications, radar, GPS… • We make electrons do useful things. >1020!

  3. Making electrons move - + - - - - - - 1.5 volts - - - - - - - - - - - - - - - -

  4. 9 volts 120 volts 170 volts peak! Voltage: determines how hard the electrons are pushed.

  5. 2N 3904 Parts List • Resistors • 1,000 ohms: • 10,000 ohms: • 100,000 ohms: • Light emitting diode (LED) • Photoresistor • Transistor

  6. Horizontal rows of 5 are connected All holes in each vertical column are connected The Power Supply and Protoboard set to 10 volts V- V+

  7. Circuit #1 switch the meter to measure current mA V V- V+

  8. - + The Results: The Schematic 10 volts LED Resistor Current: tells us how many electrons pass through the circuit every second. Resistor: resists the flow of current…like putting a kink in a garden hose.

  9. Our night light needsa device thatcan “see” light

  10. Photoresistor photons more light  more electrons  lower resistance

  11. Circuit #2 more light… lower resistance… brighter LED… backwards!

  12. Tricking the electrons Circuit #3 

  13. - + - + - - photoresistor: low R photoresistor: high R LED LED 10,000 ohms 10,000 ohms How does circuit #3 work?electrons take the path of least resistance

  14. Actually, the current is in the direction of positive charges …thank you, Ben Franklin! - + - + + + photoresistor: low R photoresistor: high R LED LED 10,000 ohms 10,000 ohms

  15. We need amplification! …the LED is too weak…

  16. V+ large current small current small current large current large current large current The Transistor V+

  17. Circuit #4: the night light • the transistor has a flat face • the 1,000 ohm resistor is on top • the 100,000 ohm resistor is on the bottom • don’t forget the wire! 100k wire!

  18. - + How does this circuit work?remember, electrons take the path of least resistance LIGHTS ON photoresistor: low R + 100,000 ohms Transistor LED 1,000 ohms

  19. - + + How does this circuit work?remember, electrons take the path of least resistance LIGHTS OFF photoresistor: high R + 100,000 ohms Transistor LED 1,000 ohms

  20. QUESTIONS?

  21. Supplemental Materials

  22. Electronic Night Light Parts List 1000 RESISTOR (5%) (brown-black-red-gold) 10,000  RESISTOR (5%) (brown-black-orange-gold) 100,000  RESISTOR (5%) (brown-black-yellow-gold) CdS Photoresistor (note: the 100k resistor may need to be replaced with a larger or smaller value depending on the characteristics of the CdS photo resistor available.)  Light emitting diodes (red, yellow, and/or green)  Transistor (Part no. 2N3904) 1 – Protoboard; 1-Power supply or 9v battery; hook-up wire and wire cutters

  23. Written by J. Hopwood ECE Department, Northeastern University Title page photo credit: Prof. N. McGruer This lab is intended for college freshmen or high school students considering a career in engineering. It was developed for the “Building Bridges” program of Northeastern University, Boston, MA with support from the National Science Foundation.

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